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Labeo rohita and Its Life History

Labeo rohita is the important food fish that belongs to the carp family Cyprinidae under order Cypriniformes of Class Actinopterygii. There are three crucial Indian major carp (IMC) such as, Labeo rohita, Catla catla and Cirrhinus cirrhosus, of which Labeo rohita is the most highly market-priced carp fish due to its attractive taste. It is also known as rui, rohu, or roho labeo. It can tolerate a wider temperature range, and it is the most adaptable and important cultured fish species in Bangladesh, India, Pakistan, and Myanmar.

Systematic Position

  • Phylum: Chordata
  • Sub phylum: Vertebrata
  • Class: Actinopterygii
  • Order: Cypriniformes
  • Family: Cyprinidae
  • Subfamily: Labeoninae
  • Genus: Labeo
  • Species: Labeo rohita Hamilton, 1822

Synonyms

Cyprinus rohita; Hamilton, 1822; Labeo rohita; Day, 1878; Shaw and Shebbeare, 1937; Labeo rohita; Bhuiyan, 1964

Fin Formula

D. 15-16 (3/12-13); P1. 16-17; P2. 9; A. 7(2/5). (Rahman, 2005)

Physical Description

There is a proverb in Bengali that Rui (Rohu: Labeo rohita) is the king of fish, and Pui (vegetable) is the king of vegetables. So Rui is known to everyone as a very popular and delicious fish. The body of the rohu fish is spindle-shaped, and both sides of the body are symmetrical and flat. The head and tail are gradually narrower, but the head is 4-5 inches long. The dorsal part of the body is convex, but the surface of the head is more convex than the abdomen.

The snout is blunt, low, rarely swollen. The mouth is downward, and the lips are thick and fringed above and below the mouth, which is folded inwards. The mouth is located at the bottom region; the two corners of the mouth are curved backward, so the mouth is crescent-shaped. There is a pair of nostrils just in front of the eyes on the surface of the snout. The eyes are large in shape and have no eyelids. The cornea is transparent, which is covered by skin.

The whole body is covered with silver scales. The scales are smooth and arranged in rows. The upper lip of the mouth has a pair of barbells. The gill covers are wide. The surface scales of this fish are reddish, and the edges are black. This reddish color in the center of the scales becomes darker and brighter during the breeding season. Their dorsal and below the dorsal sides are brown, and their bellies are silvery white.

Their lateral line is complete, and there are 41-42 scales along this line. The dorsal fin has 15-16 soft rays, of which the first three rays are longer than the other rays. There are 16-17 soft rays in the pectoral fins, 9 in the pelvic fins, and 8 in the anal fins. The caudal fin is more bifurcated, and the caudal peduncle is short. They grow up to 200 cm in length and up to 45 kg in weight. They can live up to a maximum of 10 years. In Bangladesh, they are also called as Rohita, Ruhit, Rau, Nala, Garma, Naosi, etc.

Habit and Habitat

Apart from Bangladesh, this fish is found in North and Central India, Pakistan, Nepal, and Myanmar. They are usually river fish but also found in all freshwater bodies such as canals, beels, haors, baors, floodplains, ponds, streams, ditches, marches, etc. They are column feeders and mainly feed on plant-based food. Due to their slightly downward mouth with thick lips, they feed on aquatic plants, weeds, and occasionally take the rotten organic matter from the bottom region. When they are immature, they eat plankton. They also take fish meal, mustard oil cake, rice corn, etc. as supplementary food during cultivation in ponds.

Reproduction

They reach sexual maturity within two to three years. During the monsoon season, females and males take part in reproduction in flooded rivers, especially in aquatic vegetation areas. In one breeding season, a mother fish lays about two to thirty lac eggs, which can be more or less depending on the age, length, and weight. It also depends on the length and weight of the ovaries of fish. They lay their eggs in relatively shallow water and on the banks of rivers. Also, if artificial currents are created, rui fish can lay eggs in dams or ponds, without any worries. They usually lay eggs from June to August.

Embryonic Development of Labeo rohita

The diameter of fully swollen fertilized eggs is 4.1-4.8 mm, but their average diameter is 4.5 mm. The first cleavage occurs 45 minutes after fertilization. The second cleavage occurs within the next 5-6 minutes. The third cell division occurs within the next 15-20 minutes. The yolk invasion is half completed within 2 hours of fertilization. It reaches the Yolk plug stage in the next 1 hour.

Embryos can be identified 4 hours after fertilization. In the next 1 hour, the cluster of yolk becomes longer. A myotome is seen within the next 1 hour. In this stage, the head and tail part of the fetus is formed, the optic cup and 7-10 myotomes are also seen. Within 8 hours, 17 myotomes and capfer vesicles are seen, and the fetus begins to move. Eggs start hatching 14-18 hours after fertilization.

image of Embryonic development of Rui

Figure: Embryonic development of Rui fish: Fertilized egg- (a) Newly formed bastodisk; (b) 2-cells phase; (c) 4-cells phase; (d) 8-cells phase; (f) 18-cells phase; (g) morula phase; (h) yolk plug phase, embryo; (i) elongation phase of yolk cluster; (j) About 2 hours before hatching.

Table: Different stages of larval life of Labeo rohita

Hatching

Hatching time (hours)

0

6

12

24

36

48

Average total length (mm)

3.78

4.70

5.31

5.49

5.85

6.20

Range (mm)

3.62-3.83

4.62-4.78

5.22-5.40

5.25-5.84

5.71-5.99

6.07-6.33

Length of yolk sac (mm)

2.52

2.94

3.15

2.79

2.52

2.90

Maximum height of yolk sac(mm)

0.72

0.70

0.75

0.45

0.45

0.36

Body height along the dorsal fins (mm)

0.90

1.00

1.08

0.90

0.90

0.90

Number of pre-anal myotome

26

26

26

26

26

26

Number of post-anal myotome

14

14

14

14

14

14

Eye diameter (mm)

0.18

0.20

0.27

0.28

0.28

0.30

Eye color

Light yellow

Yellowish brown

Black in the middle

Black in the middle

Dark black

Black centered eye

Length to the rear end of the notochord (mm)

3.62

4.50

5.05

5.35

5.53

5.40

Direction of movement

Irregular movement, rarely twisting up or staying sideways at the bottom.

Irregular movement, comes from the bottom to the surface.

Moves vertically, occasionally climbs up obliquely and does not take no rest.

Performs vertical movements.

Moves slowly with occasional jerking.

Moves slowly with occasional jerking.

Dorsal fin

Absent

Absent

Absent

Buds may be seen.

Present

Well-defined

Larval Development of Labeo rohita

Hatchling

The yolk gradually becomes slender. Like the Mrigel and Catla, the embryos are similar in width from the posterior part to the yolk. The bulbous part of the anterior part of the yolk cluster is noticeable. The long slender part of the yolk cluster is smaller than Mrigel. Like other Puntius species, the heart is located in front of the yolk sac. A light pink marked posterior blunt part is seen on the dorsal part of the yolk. The eyes are slightly yellowish-brown.

image of Hatchling of Rui fish

Fig. Hatchling of Rui fish

6th Hours After Hatching

Dorsal fin buds are absent. The fetus moves irregularly. Rarely moves from the bottom to the top or rests on the bottom.

12th Hours After Hatching

Chromatophore can be seen only in the eye. The center of the eye to turn black due to the presence of chromatophore.

image of 12 hour after hatching of Rui

Fig. Larva of Labeo rohita: 12th hours after hatching

​24th Hours After Hatching

Some black chromatophores are seen on the dorsal edge of the yolk sac. Gill arch becomes distinct. The tail looks like spatulate. There are a few black chromatophores on the head above the eyes. The color of the embryo is light yellow. The anus is clear. The auditory organ is completely distinct. The yolk sac is sharply attached to a sharped distal point. Various spots can be seen on the caudal fin. The notochord bends upwards. The pectoral fins do not have any fin rays.

image of 24th hours after hatching of rui

Fig. Larva of Labeo rohita: 24th hours after hatching

​36th Hours After Hatching

Lower lips become clear. The pectoral fins become apparent. A few black chromatophores are found on the whole dorsal edges of the yolk sac, the head and dorsal fins. No chromatophore is seen in the caudal region. The dorsal and ventral sides of the fetus are light yellow, but from the back of the tail region to the anus is dark black. The top of the notochord is bent upwards. The mouth exists as a tiny hole.

image of 36th hours after hatching of Rui

Fig. Larva of Labeo rohita: 36th hours after hatching

​48th Hours After Hatching

The tip of the yolk sac is slightly convex like a catla, but it is not as straight as a mrigel carp. The embryos are yellow. The swimbladder is distinct, and the pectoral fins are noticeable. There is no chromatophore on the ventral side of the swimbladder. A row of black chromatophores can be seen from the posterior region on the right side of the auditory node to the base of the caudal fin. 

The black chromatophores on the top of the head are apparent, and the chromatophores that spread to other parts of the body are large. Like the Mrigel fish, the pelvic embryonic fin folds begin at the front of the dorsal early fin folds. These fin folds do not contain any chromatophores. The gill arches are apparent, and the swimbladder is oval. The head is dark, and the body is slightly yellow.

image of 48th hours after hatching of Rui

Fig. Larva of Labeo rohita: 48th hours after hatching

72nd Hours After Hatching

The larval length is 6.95 mm. Its color is light yellow. The swim bladder is oval. Gill arch becomes specific. Some black chromatophores are seen on the head and the two eyes.  The dorsal region to the anal area of the fetus is bright yellow. The tail region is yellow on the notochord.

Post larval development of Labeo rohita

96th Hours or 4 Day After Hatching

At this time, the length of the fish is 7.57 mm. Yellow chromatophores are seen in the head region behind the eye. The opercular part is distinct. The top of the notochord is curved. There are rows of distinct black chromatophores along the entire length of the lateral side of the embryo. Most larvae have an apparent reddish spot slightly above the anus. Yellow sac formation and caudal fin ray formation become completed. The two lips are of the same type but somewhat fimbriated type.

Under a magnifying glass, there is a crescent-shaped black region made of chromatophore in the tail region below the notochord. The chromatophores are densely embedded to form a straight line of a semicircle with a transparent area in the center. This semicircle is not continuous but apparent. Dorsal and pelvic fins folds exist.

image of 4th days after hatching of Rui

Fig. Post larva of Labeo rohita: 96th hours or 4 days after hatching

5th Days After Hatching

At this time, the length of the fish is 8.5 mm. In most cases, prominent red spots are seen in the abdominal area. The swim bladder is oval. It is partially covered with black chromatophores. No chromatophores are seen in the folds of the dorsal and ventral embryonic fin folds. No rays can be seen in the folds of the dorsal fin. 5-7 rows of black chromatophores are seen on the body. The number of caudal fin rays is about 8-10. Black chromatophores are irregularly arranged in the caudal region.

image of 5th days after hatching of Rui

Fig. Post larva of Labeo rohita: 5th  days after hatching

6th Days After Hatching

The length of the fish is 10.5 mm. There are nine fin rays in the dorsal fin. Unclear rays can be seen in the anal fins, while buds can be seen on the pelvic fins. A few dark black chromatophores can be seen on the head. The dorsal side of the fetus is yellow. The swim bladder is divided into two parts. The anterior part of the fetus is round, and the posterior portion is long triangular. Black chromatophores cover both parts of the swim bladder.

The body has 7-8 rows of black chromatophores. The number of caudal fin rays is 22. On either side of the caudal fin, two black crescent-shaped bands are separated by a small pigment-free area. Black chromatophores can be seen below the notochord on the caudal peduncle. The caudal fins are slightly less forked than those of catla and mrigel fish. The ratio of the total length and the length of the base of the dorsal fin is 6.4: 1.

image of 6th days after hatching of Rui

Fig. Post larva of Labeo rohita: 6th days after hatching

7th Days After Hatching

At this time, the length of the fish is 11 mm. Lips are thick. The top of the notochord is curved upwards. The ventral embryonic fin folds extend from the abdominal region to the anal fins while the dorsal embryonic fin fold is situated opposite to the anus. There is no pigment in the membranous junction area of the body. However, there are a few orange dots. There are two spots of black chromatophore on the caudal peduncle at the back of the origin of the fins ray. The caudal fin is less deeply forked than Catla and Mrigel carp, which contains 22 branched fin rays. There are few chromatophores at the base of the anal fins.

The pelvic fins have 2 or 3 fin rays with no chromatophore, while the dorsal fin contains 13 fin rays with no chromatophores at the margin of the dorsal fin. More chromatophores can be observed in the swim bladder region, but clear black chromatophores exist on the head. Black chromatophores are widespread throughout the body. However, the number of these chromatophores is not significant. The ratio between the total length of the body and the base of the dorsal fin is 6: 1.

image of 7th days after hatching of Rui

Fig. Post larva of Labeo rohita: 7th  days after hatching

8th Days After Hatching

At this time, the length of the fish is 12.5 mm. The dorsal fin has 14 rays, and a yellowish pigment is scattered near the base of those rays. No pigmentation can be noticed on the margins of the dorsal fins like Mrigel. The anal fin contains seven fin rays. A ventral embryonic fold is found in the anal region, which forms at the end of the abdominal area. The caudal fin provides 32 rays. The rays of the posterior part are branched. One-third of the base of these rays of this fin is orange. A few distinct black chromatophores can be noticed above the caudal peduncle. At the junction of caudal embryonic fin fold with the anal fin, a few black chromatophores and orange pigment spots are seen.

A few black and orange pigmented spots are also seen on the membranous anterior part of the caudal fin. These spots are similar to the catla but are more distinct than Mrigal. The body is golden yellow. Numerous black chromatophores are scattered throughout the body and head without any specific pattern, but it is few in the anal region. The ratio of the total length and the length of the base of the dorsal fin is 6.3: 1.

10th Days After Hatching

At this time, the length of the fish is 15.5 mm. From the thick upper lip hangs a fimbriated lower lip. There is a red mark from the anterior part of the abdominal region to the anus. There is no barbell. The color of the fish is golden yellow. The dorsal fin has 14 branched rays. Dark pigments cannot be noticed on the fins like catla. The anal fins have eight rays, and half of the base of the rays is covered with light pigment. The pelvic fin contains eight rays with no pigment. Like catla, a transparent fin fold is present that starts from the pelvic region to the anal region.

At the junction of the membranous caudal fin and the caudal peduncle is not covered by yellow pigment. There are 30 branched rays in the caudal fin. There are two light black crescent-shaped regions of the chromatophore on the caudal fin. These fins are covered by a band that extends to the tip of the posterior part of the origin. This crescent-shaped region on the caudal fin is not as clear as the catla. Such bands do not exist in Mrigal fish. The ratio of the total length and the length of the base of the dorsal fin is 5.7: 1.

image of 10th days after hatching of Rui

Fig. Post larva of Labeo rohita: 10th  days after hatching

12th Days After Hatching

At this time, the length of the fish is 19 mm. A pair of the maxillary barbell is distinct. The dorsal part of the body is colorful, and the ventral side is light yellow. 16 (3/13) rays can be seen in the caudal fin under the microscope. A yellow-orange pigment covers more than half the distance from the base of the dorsal fin. There are seven fin rays in the anal fin. The other fin rays are branched except the front one. The amount of black pigment is less on the half of the base of the fins rays than Mrigel, but it has the same as catla. The black chromatophores of the dorsal half of the body are more pronounced. The pelvic fin contains seven fin rays but no fin ray on the membranous anterior margin of the caudal fin. There are more yellow pigments on the dorsal side.

The two chromatophores are seen to merge a little behind the origin of the fins. This junction area is dark in color but not precisely crescent-shaped like catla. Orange pigments can also be noticed in this region. A wide triangular band can be observed in front of the origin of the rays on the caudal peduncle. In most cases, the band extends along the entire width of the front of the head. These chromatophores are present under the microscope, but they do not co-exist. The caudal fin contains 34 fin rays. Orange pigments are scattered in the first half of the base of these rays. The ratio of the total length and the length of the dorsal fin is 6.3: 1.

15th Days After Hatching

At this time, the larvae are 23 mm in length. There is a hanging lip with a pair of barbells. Orange pigmented spots exist on yellow pigment. Moreover, such orange spots exist among the rays of the dorsal fin. The anal fin contains 7 (2/5) fin rays. Only one-third of the base of the rays has orange pigment. Anus exists in front of the anal fins like Mrigel. However, this situation is not seen in catla.

There are seven rays in the pelvic fins. The black pigment can be seen on half of the base of the pelvic fin. There is a clear band of black chromatophores along the entire length fin ray in front of the caudal peduncle. The origin of the caudal fin ray is divided into two halves, and the caudal fin extends posteriorly. The number of caudal fin rays is 34. There are six unbranched fin rays on each side of the caudal fin. The ratio of the total length and the length of the base of the dorsal fin is 5.4: 1.

image of 15th days after hatching of Rui

Fig. Post larva of Labeo rohita: 15th days after hatching

18th Days After Hatching

At this time, the length of the fish is 25 mm. Black chromatophores cover the body. Such chromatophores are more abundant above the lateral line. The body color on the lateral line is light yellow. On the other hand, the lower part of the lateral line is yellowish-white. The body is covered with scales. However, the scales of the abdominal region are not clear, especially near the caudal peduncle and the abdominal region.

When the length of the fish becomes 24 mm, the first scales are observed at this time. At this stage, 4-5 rows of scales exist next to the opercular margin to the beginning of the dorsal fin. At this time, a pair of barbells also exist. Pelvic fin contains nine fin rays. The half of the base of this fin rays contain orange pigment. Two distinct gray half-crescent-shaped structures are present on each lobe of the caudal fin.

20th Days After Hatching

At this time, the length of the fish is 26 mm. There is a pair of barbells on the margin of the thick hanging lips. Each barbell originates from a notch in the mandibular region. The body is completely covered the golden-colored scales. The color of the particular part of the body above the lateral line is yellow. The color of the underside of the lateral line is light dirty yellow. The transparent black chromatophores are spread all over the body. There is a dark-colored band above and below the lateral line, which runs from the next gill cover to the caudal region.

Several black chromatophores exist along the margin of the dorsal fin. The rays of the pelvic fins are colorless and not transparent. The posterior border of the band is slightly concave, but the front edge is irregular. Two spots separate this dark band, and two light crescent-shaped areas are seen. Crescent-shaped areas contain a small black spot. This spot also exists in an outer part of the dark caudal fin band. Orange pigment covers the caudal fin rays with a few spots at the distal ends. The caudal fin contains 34 rays, the rays of the margin of each side are unbranched.

25th Days After Hatching

At this time, the length of the fish is 30 mm. Their color is light brown with a tan hue from operculum. The barbell is noticeable. The upper margin around the eyes is slightly orange. The scales are distinct. The dorsal fins are slightly orange with small black. The base of this fin is yellow. The pelvic fin contains 7 (2/5) fin rays. Except for the one-third part of the first few rays, the other rays show orange pigment.

The rays on the back of the pectoral fins contain no pigment. The first few rays contain black and orange pigments. There is no pigment in the pelvic fins except for the second branched fin ray. The dark band in the caudal region is fully visible. Under the microscope, the band appears round. Large black chromatophores cover this band entirely. The more distinct pigment can be seen in the pelvic fins. The upper part of the caudal fin is larger and pointed, but the base is slightly smaller, and the margins are rounded.

Table: Difference among Rui, Catla and Mrigal during the development stages

Mrigal (Cirrhinus chirrhosus)

Catla (Catla catla)

Rui (Labeo rohita)

Hatchling

The thinner part of the yolk is more significant in length than the thicker part. Yolk is more or less club-shaped. Most hatchlings have 28 prenatal and 14 post anal myotomes.

The thick and thin part of the yolk is equal in length. In most cases, there are 26 prenatal and 14 post-anal myotomes.

Like catla.

24 hours after hatching:
The narrow end of the yolk sac did not end at a pointed end.

Like mrigal

The narrow edge of the yolk sac ends in a slightly pointed tip.

36 hours after hatching:
The anterior profile of the yolk sac is more or less straight.

Anterior profile yolk sac is convex.

Like catla

48 hours after hatching:
The anterior profile of the yolk sac is more or less straight.

Anterior profile yolk sac is convex.

Like catla

72 hours after hatching:

There are a few black chromatophores in the caudal region. There is no reddish impression in the operculum region.

The opercular region has a reddish tinge. There are dark and somewhat triangular spots on the caudal peduncle.

The caudal region has a few light pigmented spots behind the notochord. There is no reddish tinge in the opercular area.

96 hours after hatching:

The dorsal fins have black chromatophores at the front of the dorsal fin buds. Black chromatophores exist below the apex of the notochord. These chromatophores are confined to a semi-circular area. The reddish color is seen in the abdominal region. Such characters are not seen in Rui and catla. Lips thin. The dorsal fin is separated from the embryonic fold.

A semicircular mark with black chromatophores is seen on the ventarl side of the caudal fin just in front of the edge of the notochord. The arc of the semicircle is not clear, and the straight line of the arch is somewhat concave. The margin of the lips is thick. The abdomen above the anus has a reddish tinge. The dorsal fin is separated from the embryonic fold.

The black chromatophores lined beneath the notochord form a crescent-shaped semicircular region. In most species, a red spot is seen on the bare eye just above the anus at the beginning of the pelvic fins fold. The edges of the lips are slightly fimbriated.

Five days after hatching:

The number of caudal fin rays is 7. They are not branched. There are no rays in the front part of the dorsal fin. As a result, it separates from the embryonic fold.

At the bottom of the notochord, 18 rays are visible, with branches at their distal ends. On the front of the dorsal fin, there are six rays which are different from the embryonic folds.

About 8-10 fin rays are seen in the caudal fin. They are branched. In most cases, the abdomen is clearly reddish. At this stage, dorsal fins are seen, which are different from embryonic folds.

Six days after hatching:

The dorsal half of the body is yellowish-green. There are crescent-shaped two light marks on the caudal peduncle. Anal fins exist.

The body is light yellow. The caudal region has two crescent-shaped regions with chromatophores. Anal fin absent.

The dorsal part of the body is yellow. The two crescent-shaped parts made of chromatophore on the two lobes of the caudal fin, which are separated by a colorless area. Anal bud exists.

Seven days after hatching:

On the caudal peduncle, a triangular structure formed by black chromatophore that can be seen in front of the origin of the caudal fin ray. The caudal fin is not as deeply forked as the catla. The dorsal fin is completely separate from the embryonic fin fold. From the front of the membranous part of the caudal fin to the beginning of the caudal fin ray, a clear yellow pigment is spread.

Two small crescent-shaped structures with black chromatophores are present just behind the beginning of the caudal fin.  The caudal fins are more forked than Mrigel and Rui. The dorsal fin is completely separated from the embryonic fold. There is no yellow pigment from the front of the membranous part of the caudal  fin to the beginning of the caudal fin ray.

Two clusters of black chromatophores exist on the caudal peduncle. The caudal fin is less forked than catla. The dorsal fin is completely separated from the embryonic fold. There are several spots of orange pigment from the front of the membranous part of the caudal fin to the beginning of the caudal fin ray.

10 days after hatching:
Lips thin, like full-grown adults. There is no black chromatophore at the margin of the dorsal fin. A triangular area with black chromatophores can be seen just in front of the origin of the caudal fin.

Lips thick. The mouth is slightly upward. The margin of the dorsal fin is dark blue due to chromatophore. Somewhat anterior to the origin of the fin ray, there are two distinct chromatophores on the caudal peduncle. A triangular region with black chromatophores is present below the notochord. This region is less clear than Mrigel.

The thick fimbriated upper jaw is present, which hangs over the lower jaw. There are no chromatophores on the margin of the dorsal fin. Two faint black chromatophores exist on the caudal fin ray. Beneath the sharply curved notochord, there is a triangular region with a more or less broad base formed by black chromatophores. Each chromatophore is clear.

15 days after hatching:
The dorsal half on the body, especially on the lateral line, is richer in pigment than the rui and catla. As a result,  a thin dark parallel line exists on the yellow tinge. There is no crescent-shaped pigment in the tail region. Scales can be seen.

The margins of the dorsal fin are black. Two-third part of the dorsal fin ray from the base is covered with light yellow pigment. Black chromatophores cover the triangular-shaped region on the caudal peduncle. Scales are not seen.

Thick hanging lips. Two barbells can be seen. Two-third of the base of the dorsal fin is orange pigmented. The caudal fin region contains black chromatophores that lengthen posteriorly, which  divide the caudal fin into two lobes. Scales are not seen.

Economic Importance

It has a high demand in the market due to its attractive taste. Besides, its nutritional value is very high. For every 100 grams of rui fish contain 16.4 grams of protein, 1.4 grams of fat, 680 mg calcium (Ca), and 223 mg phosphorus(P). In Bangladesh, Rui, Catla, and Mrigel fish account for 22.5% of the total fish production.

Reference

Chakraborty, R.D. and Murty, R.S.V. 1972. Life history of Indian major carps, Cirrhina mrigala (Hamilton), Catla catla (Hamilton), and Labeo rohita(Hamilton). Journal of Indian Fisheries Society of India. 4:132-161.

Kabir, A.K.M. N. and Mia, Mohiuddin. 2018. Fisheries Biology(in Bengali). 2nd edition. ATM Publications, 38/3, Banglabazar, Dhaka. pp. 623.

Rahman A. K. A. 2005. Freshwater Fishes of Bangladesh. 2nd  edition. Zool. Soc. Bangladesh. pp. 394.

Shafi, M. and Quddus, M. M. A. 2003. Bangladeshher Matshya Sampad (in Bangali). Kabir Publications, 38/3, Banglabazar, Dhaka. pp. 345.

Catla catla and Its Life History

Freshwater fish live in freshwater habitats such as rivers, lakes, streams, ponds, ditches, marshes, flood plain, etc. About 41.24% of all known fish species occur in freshwater. The most notable freshwater fish species are Rohu, Catla, Mrigal, etc. In this article, we will discuss about the Catla calta and its life history.

Systematic Position

  • Phylum: Chordata
  • Sub phylum: Vertebrata
  • Class: Actinopterygii
  • Order: Cypriniformes
  • Family: Cyprinidae
  • Sub family: Cyprininae
  • Genus: Catla
  • Species: Catla catla Hamilton,1822

Synonyms

Cyprinus catla Hamilton, 1822; Catla catla (Hamilton, 1822); Catla buchanani: Day, 1878; Leuciscus catla (Hamilton, 1822); Cyprinus abramioides Sykes, 1839; Hypselobarbus abramioides (Sykes, 1839); Catla catla Shaw and Shebbeare, 1937;

Fin Formula

D. 17-18(2/15-16); P1. 18-20; P2. 9; A.8 ( 3/5) (Rahman, 2005)

Physical Description

Catla is a well-known fish of the Family Cyprinidae under the order Cypriniformes. This fish is very wide in proportion to its body length, its head and mouth are quite large. The space between the eyes is slightly convex. Two pairs of nostrils present. Each pair is located at the top of the front of the eye.

The mouth and pharynx are wide. The maximum depth of the body is in front of the dorsal fin. They have no barbells. The lateral line organ is complete. There are 40-43 scales along this line. The dorsal fin is long. The pectoral fin does not reach the pelvic fins but the pelvic extends to the anal fin. The caudal fin is deeply bifurcated.

There are big size scales in the body. The surface of the body is gray, the sides of the body are silver and the abdomen is white. The fins are also black, but the pectoral fins are much whiter. The number of their branchiostegal rays is III. There are usually 17-18 soft rays in the dorsal fin, 18-20 in the pectoral fins, 9 in the pelvic fins, 8 in the anal fins and 19-20 in the tail fins.

This fish is fast-growing and can grow up to four kg in one year and ten kg in two years if it gets sufficient food. The maximum length of Catla fish can be up to 1.80 m. Catla fish can weigh up to a maximum of 45-50 kg.

Habit and habitat

The mouth of the Catla fish is slightly upward. They feed on the surface of the water. Apart from that, they are accustomed to pick and eat small food particles. They cannot take any food from the bottom and they cannot afford to eat aquatic weeds.

Catla eats more phytoplankton than zooplankton. They eat the most food from 8-9 am (Jana and Chakrabarti, 1988). However, according to Shafi and Quddus (2001), there is still a tendency to eat from noon to evening. Four-day-old fry eats Brachionus spp., Ceriodaphnia spp. and Moina spp. Etc, (Chakrabarti and Sharma, 1997; Kumar and Chakrabarti, 1998; Kumar et al., 2000).

Large-sized Catla prefers to eat plankton both Phytoplankton and zooplankton (Natarajan and Jhingran, 1961; Jhingran, 1991). They also eat aquatic insects, rotting garbage, algae, and aquatic plants. When cultivating in the pond, fish meal, mustard oil cake, rice corn, etc. are taken as a supplementary food.

Catla fish live in major rivers of Bangladesh including Buriganga, Meghna, Beel, Haor, and Baor (Oxbow lake). It is also seen in paddy fields during monsoon. They can also live in stagnant waters. They are also found in large numbers in India, Pakistan, and Myanmar.

Table: Percentage of food intake at different stages of life of Catla catla

Food types

Fingerlings

Juveniles

Adults

Algae

<11.2

19.8

27.3

Detritus

<5.6

17.2

26.8

Invertebrates

<5.9

57.3

39.5

Aquatic plants

-

5.9

6.4

Data source: (1) Mohanty (2003); (2) Natarajan and Jhingran (1961)

Reproduction

 Catla fish usually breed at the age of 3-5 years.  They usually lay eggs in May-June. They do not lay eggs in stagnant water, but they lay eggs in relatively shallow water and in flowing rivers. An adult fish can lay 1.5-2.0 lac eggs. The eggs are neither floating nor sticky. Eggs are light red in color with 4.5-5.4 mm in diameter.

Embryonic development of Catla catla

Segmentation begins 35-40 minutes after the fertilization of eggs. The diameter of a mature egg is 4.5-5.4 mm with averages of 5.0 mm in diameter (Figure-2). 2nd and 3rd cleavage occur every 10 minutes. Within 1 hour 45 minutes, it reaches the Morula stage. Yolk invasion is half done in 3 hours and reaches the yolk plug stage in 2 hours. In the next 30 minutes, the yolk plug stage becomes longer and the myotome is seen after 6 hours of fertilization. After that, the head and tail areas begin to separate.

When 17 myotomes are seen, the clusters of yolk spread up to the tail region. Kupffer`s vessels and auditory vessels are seen at this time. About 9 hours after fertilization of eggs, the fetus begins to vibrate gently. Egg hatching is completed within 15-16 hours.

image of Embryonic development of catla catla

Figure: Embryonic development of Catla fish: fertilized egg- (a) newly formed bastodisk; (b) 2-cell phase; (c) 4-cell phases; (d) 8-cells phase; (e) 16-cells phase; (f) Morula phase; (g) Yolk plug phase, embryo; (h) Yolk plug elongation phase;  (i) About 2 hours before hatching.

Table: Different stages of larval life of Catla

Hatching

Hatching time (hours)

0

6

12

24

36

48

Average total length (mm)

4.68

4.80

5.60

5.80

6.40

6.48

Range (mm)

4.62-4.73

4.75-4.84

5.50-5.70

5.54-6.16

6.21-6.58

6.18-6.63

Length of the yolk sac(mm)

3.06

3.14

3.20

2.72

2.90

3.06

Maximum length of yolk sac(mm)

0.99

0.86

0.83

0.80

0.55

0.36

Body depth along the dorsal fin (mm)

0.99

1.00

1.30

1.16

1.30

1.08

Number of pre-anal myotome

26

26

2626

26

26

26

Number of post-anal myotome

12

12

12

12

12

12

Eye diameter (mm)

0.20

0.20

0.30

0.30

0.35

0.36

Eye color

Colorless

About colorless

The center is black

black

Dark black

Dark black

Length to the rear end of the notochord (mm)

4.60

4.70

5.40

5.68

6.12

6.25

The direction of movement

Irregular movements can be noticed. Rarely rising up in a twisted position or resting laterally at the bottom.

The movement is weak, resting laterally at the bottom of the habitat, rarely coming to the surface.

Moves vertically, occasionally rising obliquely upwards.

Moves slowly by shaking, sometimes move horizontally

Moves slowly by shaking, sometimes move horizontally

Cell

Pectoral fin

Absent

Absent

Absent

Buds may be seen

Present

Present

Larval development of Catla catla

Hatchling

The bulbous and slender parts of the yolk are of equal lengths, like a Mrigel fish. The eyes are obvious. No chromatophore was observed.

image of Hatchling of Catla

Fig. Hatchling of Catla

6th hours after hatching

The movement of the hatchling is very feeble. They rest on the side of the dwelling and rarely come to the surface. The eyes are colorless in most cases.

12nd hours after hatching

The body color is yellowish on the dorsal side above the yolk sac. Buds are not seen on the pectoral fins.

image of 12th hours after hatching of Catla

Fig. Larva of Catla catla: 12nd hours after hatching

24th Hours After Hatching

Buds can be seen on the pectoral fins. The movement of the larvae is fast. They begin to vibrate horizontally. They rest on the side of the dwelling. Black chromatophores exist on the upper edge of the yolk sac. There is more pigment in the eyes than on the edges of the eye. The tail fins are of the spatulate type. Spots can be seen on the fins. The narrow edges of the yolk, gradually become ribbons like shape. The position of the mouth is seen just like a small hole. Such pores are also seen in Mrigel fish.

image of 24th hours after hatching of Catla

Fig. Larva of Catla catla: 24th  hours after hatching

36th Hours After Hatching

The dorsal part of the embryo is yellow. A few black chromatophores are seen on the dorsal side of the posterior myotome and yolk sac. However, there is no chromatophore above the head. The tip of the notochord is slightly curved upwards.

image of 36th hours after hatching of Catla

Fig. Larva of Catla catla: 36th  hours after hatching

48th Hours After Hatching 

The dorsal part of the embryo is yellow, the rest is dark yellow. There is a groove on the yolk on which a swimbladder is present and it is covered by black chromatophore. The front of the yolk is not concave. Rows of black chromatophores precisely begin from the auditory sensory part of the tail region. The embryonic dorsal fins fold begin from just behind the pelvic fins. The pectoral fins are distinct and they are like paddles.

image of 48th hours after hatching of Catla

Fig. Larva of Catla catla: 48th  hours after hatching

72nd Hours After Hatching

At this time the larvae are 7.3 mm long. The larvae are externally bright yellow in color and the head region is dark green in color. The eyes are apparent (Figure 9A). The operculum or gill cover area has a reddish spot. 

A series of black chromatophores are seen behind the eyes that extend from the pelvic region to the caudal peduncle. At this time, chromatophores are distinct up to the anus. Black chromatophores exist in a triangular region above the caudal peduncle below the notochord. Embryonic pelvic and dorsal fin folds exist. Yellow pigment is present on the dorsal side of the notochord at the caudal peduncle region.

image of 72nd hours after hatching of Catla

Fig. Larva of Catla catla: 72nd  hours after hatching

Pos-larval development of Catla catla

96th Hours or 4 Days After Hatching

At this time the larvae are 7.56 mm long. The edges of the lips are thick. The yolk sac is completely absorbed. There is a reddish spot all around eyes with a dark black center. A reddish color spot is seen on the anal vertebrae. The dorsal fin is separated from the embryonic fold

image of 96th hours after hatching of Catla

Fig. Post larva of Catla catla: 96th hours after hatching

5th Days After Hatching

The length of the fish is 9 mm. Dorsal and ventral  embryonic folds are present and do not contain chromatophores.  The anterior part of the dorsal fins fold has 6 fins rays. The caudal fins have 18 distinct fin rays. The notochord bends sharply upwards. The margins of the rays become branched rays, but no such condition is observed at the edges. 

Black chromatophores are more widespread on the body than at the edges of the body. However, the pigmentation under the notochord of the caudal region in Catla is more pronounced. There are two crescent-shaped black chromatophores at the beginning of the origin of the caudal fin rays. The lower lip is slightly thicker and is located below the upper lip.

image of 5th days after hatching of Catla

Fig. Post larva of Catla catla: 5th  days after hatching

6th Days After Hatching

At this time the length of the fish is 11 mm. Buds exist in pelvic fins. The dorsal fin contains 11 rays. The swimbladder is divided into two parts. The anterior part is reddish and the posterior part is long. Pigmentation can be observed in the part of the caudal peduncle from which the rays have started to be generated. The caudal fin contains 20 fin rays. The ratio between the total length and the length of the base of the dorsal fin is 5.4: 1.

image of 6th days after hatching of Catla

Fig. Post larva of Catla catla: 6th days after hatching

7th Days After Hatching

The length of the fish is 12 mm. The dorsal fin has 14 rays. The embryonic fins fold reaches up to the tail region. Pelvic embryonic fins fold exists. The caudal fin of the Catla is more forked than the mrigel fish. It is colorless but orange pigmentation can be noticed in some places on the dorsal part of the fins. 

Behind the notochord, there are two unclear crescent-shaped regions which are formed by black chromatophores. The number of caudal fin rays is 22. The ratio of the total length and the length of the base of the dorsal fin is 5: 1.

image of 7th days after hatching of Catla

Fig. Post larva of Catla catla: 7th days after hatching

8th Days After Hatching

The length of the fish is 12.5 mm. At this time 15 fin rays are seen on the dorsal fin. The margin of the dorsal fins is not black like mrigal fish. The anal fins are connected by 7 rays. There is no chromatophore at the membranous junction of the caudal peduncle and the caudal fin. 

The caudal fin contains 24 fin rays. At the base of the caudal fin, there is a dull yellow pigment. There are no fin rays in the pelvic fins. The ratio between the total length and the length of the base of the dorsal fin is 3: 1.

10th Days After Hatching

The length of the fish is 16.5 mm. The position of the mouth is like that of an adult fish. The body is golden yellow. There is no barbell. The rear tip of the notochord is sharply curved upwards. There is a thin embryonic fins fold that starts from the tip of the pelvic fin and ends at the anal fin. 

There are 17 fin rays in the dorsal fin. Up to the last 4 rays of the dorsal fin, black chromatophores are seen along the edges of the fins. Half of the base of the fin rays is covered by yellow pigment. There are 8 rays in the anal fins and 30 rays in the caudal fin. Black spots of two specific chromatophores exist in the caudal peduncle. The front margins of all these spots are somewhat concave. The chromatophores form a black triangular structure below sharply curved notochords. This structure is more or less noticeable from the marginal area. 

Pelvic fin contains 9 specific fin rays. The rays of the pectoral fins are less clear. Chromatophores are widespread throughout the light yellow colored body. There is a star-shaped black chromatophore above the head. The ratio of the total length and the length of the base of the dorsal fin is 5:1.

image of 10th days after hatching of Catla

Fig. Post larva of Catla catla: 10th days after hatching

12nd Days After Hatching

The length of the fish is 19 mm. The dorsal fins have 19 fin rays. A line of black chromatophores can be seen in the anterior margin of the dorsal fin. 8 rays can be noticed in the anal fins. Except for the first two rays of the anal fin, the others are branched. The membrane is present between the pelvic and anal region. The ventral region is transparent but has no yellow pigment. However, small black spots of pigment are spread on it. 

Pelvic fin contains 9 fins ray. The pectoral fins do not contain any chromatophores. The caudal fin contains 32 fin rays. The pigment is centered on the caudal peduncle to form a triangular structure with two crescent-shaped black chromatophores. There is no ray in the membranous part of the caudal fin and this part is covered by black chromatophore. 

The dorsal fin membrane is covered by yellow pigment. The caudal fin rays are covered by yellow pigment. The dorsal part of the body with dark black chromatophores is light yellow. The ratio of total length and the length of the base of the dorsal fin is 5: 1.

15th Days After Hatching

The length of the fish is 23 mm. The dorsal fins have 19 fin rays, of which the first three fin rays are unbranched. The apex of the dorsal fin is covered by yellow pigment. The entire edge of the fin rays looks black as it is covered by a completely black chromatophore. The anal fins have 6 rays, of which the first two fin rays are unbranched. 

The pelvic fin contains 9 fin rays. The caudal fin has 32 rays, of which the dorsal and ventral margins of the first 7 fin rays are unbranched. There is a triangular region on the caudal peduncle with black chromatophores whose base region is transparent but the apex is not clear. Behind this region, there are two crescent-shaped black condensed areas at the origin of the caudal fin. 

These crescent-shaped structures form black color by adding chromatophores. Black chromatophores are widespread throughout the body. The dorsal side of these chromatophores is yellow. The chromatophores of the head are black. The ventral region of the body contains a small number of chromatophores. The ratio of the total length and the length of the base of the dorsal fin is 5: 1.

image of 15th days after hatching of Catla

Fig. Post larva of Catla catla: 15th days after hatching

18th Days After Hatching

The length of the fish is 27 mm. The upper and ventral sides of the lateral line organ are not completely covered by rows of scales. When the length of the fish is 24 mm, the formation of scales begins. The formation of the first scales begins from the back of the operculum.

 A distinctly crescent-shaped light black structure is present on each caudal fin lobe at the base of the caudal fins. These light black long markings are seen in the triangular area of the caudal peduncle. The chromatophores of these marks are equally wide.

20th Days After Hatching

The length of the fish is 28 mm. The operculum region of fish is red. The body is completely covered by scales. Black chromatophores can be seen in the lateral line. The upper part of the lateral line is dark yellow. The chromatophores above the lateral line are more numerous in numbers and darker in color. Yellow-orange pigment is scattered on the anal fins with 8 fin rays. In most cases, the anus exists in front of the anal fins. 

On the top of the caudal peduncle, there is an incomplete light green triangular-shaped area. The tail fins are covered by light yellow-orange pigment. The triangular area on the caudal peduncle is covered by chromatophores. The edges of each of the 7 out of 34 fin rays of caudal fin are unbranched. The caudal peduncle is also covered by scales. The ratio between the total length and the length of the base of the dorsal fin is 5.7: 1.

25th Days After Hatching:

At this time the length of the fish is 30 mm. Body color is greenish yellow and operculum is reddish pink. The front edges of the eyes are light red. The edges of the upper lip are dark. The edges of the entire dorsal fin are deep and dark in color. The upper caudal fin lobe is slightly longer. 

The dorsal fin has 3/16 rays. There is a black pigment in the form of a line at the edge of the fins, but it is not as obvious as the dorsal fins. The caudal fin ray is yellow. There are light dark diamond shaped regions are seen on the caudal peduncle.

Economic Importance of Catla catla

About 23-24% of the total fish production in Bangladesh comes from catla and other major carp. Catla fish accounts for 18% of the total pond production in Bangladesh. Each 100 grams of catla fish contains 16.4 grams of protein, 2.6 grams of fat, 514 milligrams of calcium and 214 milligrams of phosphorus. It also contains 563 IU of vitamin A.

References

Chakraborty, R.D. and Murty, R.S.V. 1972. Life history of Indian major carps, Cirrhina mrigala (Hamilton), Catla catla (Hamilton), and Labeo rohita(Hamilton). Journal of Indian Fisheries Society of India. 4:132-161.

Kabir, A.K.M. N. and Mia, Mohiuddin.2018. Fisheries Biology(in Bengali). 2nd edition. ATM Publications, 38/3, Banglabazar, Dhaka. pp. 623.

Rahman A. K. A. 2005. Freshwater Fishes of Bangladesh. 2nd  edition. Zool. Soc. Bangladesh. pp. 394.

Shafi, M. and Quddus, M. M. A. 2003. Bangladeshher Matshya Sampad (in Bangali). Kabir Publications, 38/3, Banglabazar, Dhaka. pp. 345.

Mrigal Carp (Cirrhinus cirrhosus) and Its Life History

Fish is one of the major sources of animal origin protein. Fisheries have a unique role in providing employment, foreign exchange earnings, and nutrition. About 65 to 70 percent of the protein we consume every day comes from fish. 

There are various species of fish belonging to the family Cyprinidae under the order Cypriniformes. These fish are known as carp fish. Fish of this type of carp are again two types, namely Major carp and Minor carp. Carp, which is larger with more economical value, is called the Indian Major Cup such as Rui, Catla, Mrigal, etc, whereas the smaller with less important economic value are called Minor Carp, such as Kalibaus, Bata, Ghonia, etc.

The Minor Carp fish carry fewer eggs than Major Carp. Apart from our indigenous or Indian carp, there are many different types of exotic carp in Bangladesh namely: Silver Carp, Grass Carp, Bighead Carp, Black Carp, Common Carp, etc. Carp fish eat different levels of water,  so there is no competition for food and place.

 Carp species are readily available, grow very quickly, and have higher immunity. Because of its delicious taste, it is also in demand in the market, so the cultivation of carp fish is increasing day by day in many countries.

Advantages of Carp Farming

  • They eat foods from different levels of the water body.
  • They are not rivals for each other food and place.
  • They are not carnivorous.
  • They have strong immunity against diseases.
  • They grow rapidly and attain market size easily.
  • Their larvae are available.
  • Eats low-cost supplemental food.
  • Delicious to eat and high demand in the market.
  • Their economic value is high.
  • Fry can be produced by artificial breeding.

Life history of Mrigal Carp (Cirrhinus cirrhosus)

Various scientists have described the life history of the Indian Major Carp. Ahmed (1944), Alikuni and Rao(1951), Alikuni (1956)  described the early stages of minor and medium sized carp, such as Labeo gonius, L. bata and Cirrhinus reba. Khan (1925) studied on the development of Cirrhinus cirrhosus including several freshwater fish in Punjab. 

Mookerjee et.al. (1944) and Mookerjee (1945, 1946) described the identifying characteristics of freshwater fish eggs and Indian common carp fries in Bengal. Mozumdar (1951) created a key for the identification of the eggs of the freshwater fish in Bengal. Mookerjee and Mzumdar(1946) described the life history of Labeo calbasu.  Chacko and Kurian (1949) briefly described the early life history of Catla catla.

Systematic position of Mrigal Carp

  • Phylum: Chordata
  • Class: Actinopterygii 
  • Order: Cypriniformes 
  • Family: Cyprinidae 
  • Genus: Cirrhinus
  • Species: Cirrhinus cirrhosus (Bloch, 1795)

Synonyms

Cyprinus cirrhosus (Bloch, 1795), Cirrhinus mrigala (Hamilton, 1822), Cirrhina blochii (Valenciennes, 1842), Cirrhina mrigala (Day, 1878), Mrigala buchanani (Bleeker, 1860),  Cyprinus chaudhryi (Srivastava, 1968),

Physical Description

Mrigel fish is a well-known fish of the Family Cyprinidae, belonging to the order Cypriniformes. It is also called Migel or Mirka. In English, it is called Mrigal Carp, or Mrigal. Its scientific name is Cirrhinus cirrhosus. Its body is relatively cylindrical with bright appearance and the mouth is wide. 

The lateral lines are complete and there are 40-43 scales present along the lateral line. The surface is gray and the sides are silver while ventro-lateral part is gray-black and the chest, pelvis, and anal fins are of orange color. 

There are 16 soft rays present in the dorsal fins, 17 in the pectoral fins, 9 in the pelvic fins, and 8 in the anal fins. They are 25-30 cm tall and 330 grams in weight by the 1st year. In the second year, they are about 61 cm tall and about 2 kg in weight.

image of Mrigal

Mrigal Carp (Cirrhinus cirrhosus)

Habit and Habitat

They live on the bottom of the river. They are predominantly planktonic feeders but they also eat  rotten plants or plant parts (Jhingran and Khan, 1979). In the larval stage, they mainly feed on zooplankton such as nauplii, rotifers, cladocerans, and copepods (Hora and Pillay, 1962). 

According to Khan (1972) fry fish up to 100 mm in length, mainly feed on zooplankton, on the other hand with a length of 100-130 mm, fry feed on phytoplankton. Among the phytoplankton, the significant groups are Chlorophyceae, Myxophyceae, Bacillariophyceae, and Euglenophyceae. 

According to Jhingran and Khan (1979), fish with lengths ranging from 300 mm to 560 mm receive up to 65–68% of rotten garbage. They also take fish meal, mustard oil cake, rice corn, etc. as supplementary food during cultivation in ponds. 

They are mainly river fish but in Bangladesh, they are found all the freshwater water bodies such as a pond, beels, haor, baor, flooded paddy fields, and so on. Apart from Bangladesh, fish are also found in India, Pakistan.

Table: Dietary intake of fish at different life stages

Food types

Open water: River, stream

Closed water: Pond, lake, etc

Fingerlings

Juveniles

Adults

Fingerlings

Juveniles

Adults

Green Algae

5.1

5.9

14.2

3.0

6.2

10

Diatoms

4.3

8.2

10.8

6.5

12.0

13.0

Blue-green Algae

1.0

4.0

6.3

2.0

7.0

9.5

Desmids

4.1

4.0

2.0

6.0

5.1

4.1

Phytoflagellates

3.0

6.1

3.9

8.5

8.1

7.0

Algae Spores and Zygotes

15.

3.6

5.9

3.7

3.0

3.8

Microvegetation

-

2.1

1.0

1.2

1.0

-

Decayed organic matter

12.3

22.3

30.3

15.2

10.1

3.0

Protozoa

6.3

4.3

1.3

6.0

5.0

2.5

Rotifers

19.1

8.3

2.0

15.2

10.1

3.0

Crustaceans

27.3

15.1

2.5

16.4

10.0

2.0

Sand and mud

1.6

16.1

20.0

16.0

13.0

14

Data source : Khan (1972)

Reproduction

They are sexually mature within two years. During the monsoon or from May-July, they lay eggs in the aquatic vegetation in the shallow areas of the flooded river. During the breeding season, a mature female fish lays about one lac to eight lac eggs.

Embryonic development of Mrigal Carp

In the fertilized egg, the first cleavage occurs after 45 minutes of fertilization. As a result of this division, the blastodisk is divided into two distinct bastomomers. The same situation is observed in Catla and Labeo. The diameter of the fully developed egg is 4.5-5.5 mm and the average diameter is 5.0 mm. After the next 8-10 minutes, 4 cells stage are seen. In the next 10-15 minutes, 8 cells are seen. 

About 1 and 1/2 hours after fertilization, 16 blastomeres are seen. In the early stages of fragmentation, the blastoderm holds a lens-shaped through some cells. As cell division progresses, its shape resembles that of a dome and spreads over the follicle. Within 3-4 hours, half of the yolk invasion is complete and within the next hour, the reproductive ring is spread over the entire yolk, so the inferior plug layer is obtained. In the next half an hour, the initial sightings embryos are developed.

Image of In the fertilized egg, the first cleavage occurs after 45 minutes of fertilization. As a result of this division, the blastodisk is divided into two distinct bastomomers. The same situation is observed in Catla and Labeo (Figure 1). The diameter of the fully developed egg is 4.5-5.5 mm and the average diameter is 5.0 mm. After the next 8-10 minutes, 4 cells stage are seen. In the next 10-15 minutes, 8 cells are seen. About 1 and 1/2 hours after fertilization, 16 blastomeres are seen. In the early stages of fragmentation, the blastoderm holds a lens-shaped through some cells. As cell division progresses, its shape resembles that of a dome and spreads over the follicle. Within 3-4 hours, half of the yolk invasion is complete and within the next hour, the reproductive ring is spread over the entire yolk, so the inferior plug layer is obtained. In the next half an hour, the initial sightings embryos are developed.

Fig: Embryonic development of Mrigal

Fertilized Egg: (a) Newly formed bastodisk; (b) 2-cell phase;(c) 4-cell phase;(d) 8-cell phase;(e) 16-cell phase;(f) Morula phasev; (g)Yolk plug phase, embryo;(h) elongation stage of yolk cluster;(i) 6 somatic embryonic stage; (j)presence of optic cup; (k) extension of tail or tail from yolk  cluster, formation of Kupfer`s cavity; (l)  About 2 hours before hatching.

After about 7 hours of fertilization, the embryos can be separated into tail and head. The optic cup with 7 myotomes is seen in the embryo about 8 hours after fertilization. The head and tail part is not yet free from the yolk material. Then in half an hour, transparent parts (lenses) appear in the optic cup. The embryos, which are about 1/2 hours old, have a pair of autocysts and 19 myotomes. 

Kupffer`s vesicles are visible at the end of the elongate yolk part. Such vesicles can be seen when the embryos are exposed to 14 myotomes. In this phase of development, a number of embryos begin to move slowly, and as the development progresses, the movement of the embryo continues to increase. Folding wings are seen on the dorsal and ventral side of the embryo at 12 hours of aged embryos. 

Eggs begin to hatch after 16-18 hours after fertilization. This egg hatching process lasts for a few hours. The interval between the first and the last egg hatching is about 4 hours. At the time of hatching, most embryos have 42 somites.

Table showing various stages of larval life of Mrigal (Cirrhinus cirrhosus)​

Hatching

Hatching Time (Hours)

0

6

12

24

36

48

Average lotal length(mm)

4.20

4.5

5.0

6.21

6.70

6.84

Range(mm)

4.04-4.32

4.18-4.80

4.89-5.06

6.02-6.49

5.96-7.47

4.79-7.55

Length of the yolk sac(mm)

2.90

3.00

3.00

3.24

2.50

2.00

Maximum height of yolk sac (mm)

0.90

0.90

0.80

0.54

0.30

0.25

Body height along the pectoral fins (mm)

1.20

1.20

1.17

1.23

1.10

1.04

Number of pre-anal myotomes

28

28

28

28

28

28

Number of post-anal myotomes

14

1414

14

14

14

14

Eye diameter (mm)

0.18

0.20

0.27

0.27

0.40

0.40

Eye color

Colorless

Colorless

The center is black

In some cases completely black. The center contains pigment.

The center is dark black, completely covered by chromatophores.

The center is dark black, completely covered by chromatophores.

Length to the rear end of the notochord (mm)

4.05

4.35

4.80

5.85

6.30

6.60

The direction of movement

The bottom of the dwelling.

If there is light, seldom vertical movement can be noticed

Slow-moving, upward movement, rarely comes to the surface of the water.

Runs at a somewhat intense speed; some show upward and some show zigzag movements.

Some show horizontal movement.

Horizontal movement and moving at high speed.

Pectoral fin

Absent

Absent

Absent

Present

Present

Present

Larval development  of Mrigal  (Cirrhinus cirrhosus)

Hatchlings

Their bodies are transparent, with no chromatophore. The face is not formed. The slender part is longer than the bulbous part of the dumble yolk. Eyes and otocysts are clearly visible. Moreover, the anal pore exists as a shaft where the yolk sac ends.

image of Hatchling of mrigal

Hatchling of Mrigal

6 hours after hatching

There is a small dorsal shaft just behind the highest width of the yolk sacs. The notochord curves upwards from its apex. The back edge of the tail is evenly convex.

12 hours after hatching

The central pigment area of the eye is somewhat black and its border is colorless. Buccal invagination can be detected. The front of the egg yolk is globular. Pectoral fins develop poorly.

image of 12-hours after hatching-of egg

 Fig: Larva of Mrigal: 12 hours after hatching of eggs

24 hours after hatching

The mouth is clearly visible. The eyes are more black pigmented. The anal groove is obvious. From the top of the notochord to the tail fin region lined spots exist. The slender edges of the yolk are sharp.

image of 24-hours after hatching of egg

Fig: Larva of Mrigal: 24 hours after hatching of eggs

36 hours after hatching

Black chromatophores exist from the upper region of the yolk sac to the top edge of the notochord. However, there are few such chromatophores in the cranial region.

image of 36 hours after hatching of eggs

Fig: Larva of Mrigal: 36 hours after hatching of eggs

48 hours after hatching

Operculum covers the gill arches. The mouth is exposed. There is a dorsal groove in the oval region of the yolk along the upper side of the swimm bladder. At this stage the yolk sacis significantly reduced. The yolk sac  is seen  less than half the length of the embryo. The front edge of the yolk sac is straight.

image of 48 hours after hatching of eggs

Fig: Larva of Mrigal: 48 hours after hatching of eggs

72 hours after hatching

During this time the larval length is 7.20 mm. The dorsal region of the hatchling shows yellow. Clear eyes are present in these larvae. Two lateral rows of black chromatophores are seen along the body. Several prominent chromatophores are located in the abdomen and tail region behind the notochord. A group of such chromatophores also exist on swim bladder. The center of the eye is black. Throughout the lower half of the ventral side of the swim bladder, the embryonic fin buds originate. However, the dorsal fin buds originate from the posterior fossa. Only a straight row of chromatophores can be seen in the tail fin. In this situation, the lower part of the fetus, egg youlk is clearly visible.

image of 72 hours after hatching of eggs

Fig: Larva of Mrigal: 72 hours after hatching of eggs

Post-larval development

96 hours after hatching

At this time, the length of the young fisg  is 7.34 mm. The youlk sac is completely absorbed. Dark black chromatophores are seen on the head. A few such chromatophores are also observed on the dorsal fins buds. The dorso-lateral surface of the young fish  bears yellow color. A black pigmentation is seen in a semi-circular area below the anterior part of the notochord. The tail fin rays start to form. The pelvic fins become apparent; the dorsal fins begin to separate from the folds of the embryonic fins. The lips are thin at this time.

image of 96 hours after hatching of eggs

Fig: Post-larva of Mrigal: 96 hours after hatching of eggs

5th day after hatching

At this stage the length of the fingerling is 9.0 mm. The notochord curves upwards. The tail fin rays are more pronounced. The black chromatophores form a triangular spot in the peduncle region of tail. The chromatophores of the head are dark black.

image of 5 days after hatching of eggs

Fig: Post-larva of Mrigal: 5 days after hatching of eggs

6th day after hatching

At this time the length of the fish is 11.5 mm. 8 rays can be seen in the dorsal fin. A cluster of black chromatophores is seen on the 1st dorsal fin ray and the rays begin to branch out. Star-shaped black chromatophores are seen on the dorsal part of the head and body. The region from behind the eye to the caudal peduncle, the dorsal half of the body appears yellowish-green. The swimbladder is divided into two parts and the front part tends to be wider. This region is filled with black chromatophores. About 22 distinct rays can be seen on the caudal fin. Two black crescent-shaped marks are observed on the caudal peduncle. The fins of the anal fins are very weak. The ratio of the total length and the length of the base of the dorsal fin is 7 : 1.

image of 6 days after hatching of eggs

Fig: Post-larva of Mrigal: 6 days after hatching of eggs

7th day after hatching

At this time the larvae are 13.0 mm in length. 4 rays can be seen in the pelvic fins. The membranous embryonic pelvic fins begin to move from the abdomen to near the anus. The anal fins have 16 branched fin rays. 14 specific fin rays can be seen on the dorsal fin. Yellow pigmentation is seen at the base of the dorsal fin. A few black chromatophores are seen on the anterior part of the dorsal fin. The caudal fin has a membranous relationship with the body. This relationship is more pronounced on the dorsal side. 

Under the microscope, there are two unclear semicircular disc-shaped markings below the tail fin that terminate the spinal cord. At this time 22 caudal fin rays are visible. A black chromatophore cluster on the front forms a triangle-like structure. The yellow pigment can be seen halfway from the base of the caudal fin. The swim bladder is covered by black chromatophores. From the tip of the caudal fin membrane, the caudal fin rays begin which is covered by yellow pigmentation and this pigmentation is denser on the dorsal side. At this time, the ratio of the total length and the base of the length of the dorsal fin is 6.6 : 1.

image of 7 days after hatching of eggs

Fig: Post-larva of Mrigal: 7 days after hatching of eggs

8th day after hatching

At this time the length of the larva is 13.6 mm. 24 fin rays can be seen in the caudal fin. The fin rays appear yellowish up to half the length of the rays. The dorsal fin contains 16 fin rays. There are 7 fins rays in the anal fins. Black chromatophores are seen at the base of half of the tip of anal fin. Embryonic folds can be seen from the end of the abdominal region at the anal region. 

The pelvic fins have 4 rays. Black chromatophores of different shapes are scattered all over the body. The chromatophores of the head and dorsal side are more pronounced due to their dark black and star-shaped. The lips are thin. The fish is golden yellow in color. The ratio of the total length and  the length of the base of the dorsal fin is 6 : 1.

10th day after hatching

At this time the length of the fish is 15.6 mm. The dorsal side of the body is yellowish in color. With the exception of the first two rays, the remaining 14 dorsal fins are branched (Fig. 14C). One –third of the base of the fin rays is covered with yellow pigment. 26 fin rays can be seen in the caudal fin. The lateral line is visible as a dotted line. The dorsal part of the body is dark yellow, the rest is light yellow. 7 fin rays can be seen in both anal and pelvic fins. The ratio of the total length and the length of the base of the dorsal fin is 6: 1.

image of 10 days after hatching of eggs

Fig: Post-larva of Mrigal: 10 days after hatching of eggs

12th day after hatching

At this time the length of the fish is 20.5 mm. The body is more pigmented than before. The entire edge of the dorsal fin looks black, especially in the dorsal half due to the dark chromatophore. Half of the caudal fin rays are covered by a dark yellow pigment. Pelvic fins have 9 fin rays; all are branched except the 1st fins ray. 

The anal fins do not start from behind the anal opening. The first 3 rays of the anal fins are unbranched and the remaining 5 rays are branched. No barbell is observed at this time. The number of caudal fin rays is 36 which are covered with orange pigment. The tiny membranous part of the caudal fin is covered with black and yellow pigment. At this time the ratio of the total length and the length of the base of the dorsal fin is 6.5: 1.

15th day after hatching

At this time the length of the fish is 27.0 mm. The dorsal half of the body above the lateral line organ contains more black pigment. If the length of the fry is 24 mm, scales can be seen in the posterior region of operculum. The entire edges of the fins are covered with pigment. About 3/4 parts of fin length is black under the naked eye. 

The fins are covered with a yellow pigment. Moreover, a few orange dots can be seen in it. The chromatophores are clearly arranged as a thick continuous band along the fins. Under the naked eye they look like black dots. The caudal fins have 16 rays. The half of the base of the caudal fin rays is orange in color and the edges of the fins are covered by black pigment. No barbells are observed at this time. The ratio of the total length of the body and the length of the base of the dorsal fin is  6.6 : 1.

image of 15-days after hatching of eggs of Mrigal

Fig: Post-larva of Mrigal: 15 days after hatching of eggs

18th day after hatching

At this time the length of the fish is 28.0 mm. The fry are yellowish golden in color. Two black bands can be seen from operculum to the black caudal fin spot. One band is along the lateral line and the other band is slightly above the lateral line. The upper band is visible under the naked eye. 

Above the lateral line, there are black spots on a dark yellow background. The lower part has less black chromatophores than the upper part of the lateral line organ. The body is completely covered by scales. The caudal fin has 34 rays. One-third of the base of the tail fin is yellow with orange pigment spots on it. One-thrird of the front of the tail is relatively colorless. The slightly diamond-shaped black dot is located on the caudal peduncle which can be seen under the naked eye. However, under the microscope, it looks like a spade. 

20th day after hatching

At this time the length of the fish is 31.5 mm. No barbells are observed. Under the microscope, one-third of the 16 rays of the dorsal fin is covered with yellow-orange pigment. The pelvic fins are colorless. Slightly diamond-shaped black spots exist over almost the entire width on the caudal peduncle. These spots do not reach the edges. U-shaped formation is not seen on the dorsal margin of the caudal fin. 

Orange pigments are spread on the edges of the caudal fin. The body is white below the lateral line but the upper part of the lateral line is yellowish and covered by black chromatophore. The margin of the scales are black.

25th after hatching

At this stage, the length of the fingerling is 39 mm. The body is silvery with a greenish hue. There are some scales with a thin black border. The underside of the tail fin is slightly reddish in color. Orange pigments are scattered up to the tip of the caudal fins. The upper lobe of the tail fin is slightly longer than the lower lobe.

Economic importance of Mrigal Carp

Mriigel fish is very tasty and nutritious. There is a huge demand in Bangladesh as food. Mrigel fish, along with other major carp, provide 60% of total exploitation from freshwater fish in Bangladesh. Every 100 grams of fish have 19.5 grams of protein, 0.8 grams of fat, 108 kilo calories of food energy, 350 mg calcium, 250 mg of phosphorus, and 1.1 mg of iron. 

Apart from this, fishes also contain folic acid, niacin, and choline. Miguel fish have a lot of calcium and phosphorus, which contributes to bone and tooth formation. Phosphorous also removes knee pain and gout. Folic acid and iron-rich in fish help to increase blood.

References

Chakraborty, R.D. and Murty, R.S.V. 1972. Life history of Indian major carps, Cirrhina mrigala (Hamilton), Catla catla (Hamilton), and Labeo rohita(Hamilton). Journal of Indian Fisheries Society of India. 4:132-161.

Kabir, A.K.M. N. and Mia, Mohiuddin.2018. Fisheries Biology(in Bengali). 2nd edition. ATM Publications, 38/3, Banglabazar, Dhaka. pp. 623.

Rahman A. K. A. 2005. Freshwater Fishes of Bangladesh. 2nd  edition. Zool. Soc. Bangladesh. pp. 394.

Shafi, M. and Quddus, M. M. A. 2003. Bangladeshher Matshya Sampad (in Bangali). Kabir Publications, 38/3, Banglabazar, Dhaka. pp. 345.


Food and Feeding Habits of Fish

The inland water bodies consist of small aquariums to nursery ponds, canals, beels, haor, baors(oxbow-lake), rivers, streams, flooded lands, etc. These are called freshwater basins.  The more diverse fish types are found in these water bodies.

The shape, nature, feeding habits, color, etc. vary from species to species.  Their cultivation system is also different. It is important to have scientific knowledge about the nature of fish, feeding habits, diseases and so on to cultivate fish through the choice using suitable control measures.

Types of Fish

Fish are classified into the following  four types based on the type of food.

Herbivorous

This type of fish survives, grows and reproduction by eating unicellular algae, filamentous algae,  small water plants, portion of higher aquatic plants, detritus along with some mud or sand. In this case, the plant materials in their food consist of about 75% or more of the total gut contents while the animal-based food varies 1-10% in its diet.  For example, Labeo rohita, Catla catla, Labeo bata, Ctenopharyngodon idella, Amblypharyngodon mola, Oreochromis mossumbicus, etc.

Carnivorous

They take large numbers of animals as food such as Copepods, Cladocerans, insects such as beetles, water bugs, damsel flies, dragon flies, larvae, mollusks, different small fishes, tadpole larvae, etc.  Some notable carnivorous fishes are Wallago attu, Channa punctatus, channa striatus, Channa marulius, Channa gachua, Chitala chitala, Chanda nama, Chanda ranga, Rita rita, Glossogobious giuris, Mystus seenghala, Mystus cavassius, Ompok pabda, etc. Among them some are active predators such as Channa marulius, Channa striatus, Wallago attu, Chitala chitala, Mystus seenghala, etc.

Omnivorous

These types of fish eat all kinds of food. Although their favorite food is insects, they also eat vegetable-based foods such as unicellular and filamentous algae, different aquatic plants when needed. Besides, they take zooplankton such as crustaceans, rotifers, insects and its larvae, mud and sands.  During their young stage, most of the fish prefer to eat zooplankton. They consume varying percentage of plants and animal materials. 

Among omnivorous fishes, some feed on a large amount of plant materials. Some feed on equal amount of animal and plant materials while other take a greater amount of animal foods. Some important omnivorous fishes are Cyprinous carpio, Cirrhinus cirhosus, Tor tor, Puntius ticto, Puntius sophore, Puntius sarana, Gadusia chapra, Colisa fasciatus, Eutropicthyes vacha, etc.

Plankton Feeders

Some fish species take both zooplankton and phytoplankton. They take these types of food by filtering water using their gill rackers. Gizzard shad (Dorosoma cepedianum) fry feed on zooplankton until reach the length of one inch. They become a filter feeder after losing their teeth and consume phytoplankton and some tiny invertebrates. 

Menhaden (Brevoortia) is also filter feeder that prefers to feed mainly on phytoplankton. They capture phytoplankton from the water using their gill rakers.  Adult menhaden can filter 4 gallons of water per minute and receive different phytoplankton and zooplankton within their gills.  

A silver carp (Hypophthalmichthys molitrix) is also a filter feeder that has a special filtration capacity. They can filter though their gills and consume lots of phytoplankton and zooplankton.

Fish can also be classified into the following three types based on the niche they occupy in different water levels.

Surface Feeders

The uppermost layer of water, where sunlight enters, grows a large number of plankton which produce their food through the process of photosynthesis using their chlorophyll. At this level oxygen is even higher which is suitable for various animal organisms. Catla catla is mainly stay at this level to collect food. Silver Carp is also a resident of this level. Besides, Puntius ticto, Oygaster bacaila, Chanda ranga, Chanda nama, Glossogobious giuris,Tenualosa ilisha, Gadusia chapra, etc are notable surface feeder fishes.

Column Feeders

Some species of fishes take their food from the mid water. At this level water waves are relatively few but zooplankton, phytoplankton are available with sufficient amount of oxygen, suitable for fish. The fish that live here are neither true bottom nor true surface feeders. They mostly depend on the food of the middle layer of the water. Labeo rohita, Labeo bata, Tor tor, Puntius sophore, Mystus seenghala, Wallago attu, Mystus vittatus, etc are the column feeder fishes.

Bottom Feeders

The bottom feeder fish mainly depend on food for bottom organisms.  At this level, lots of benthos live here that provides nutrients to the fishes. Labeo calbasu, Labeo gonius, Cirrhinus cirrhosus, Puntius sarana, Amblypharyngodon mola, Cirrhinus reba, Clarias batrachus, Heteropneustes fossilis, Channa striatuis, Channa marulius, etc are notable bottom feeder fishes. 

The following table showing the food and feeding habits of some freshwater fishes:

Scientific Name of Fish

Order Name

Feeding Habits

Food Types

Mystus seenghala, Wallago attu,

Carnivorous and Predatory

Fish fry, insects and its larvae, fingerlings, small fishes, tadpoles, frogs, etc.

Channa marulius, Channa striatus, Chitala chitala

Cahnniformes

Carnivorous and Predatory

Fish fry, insects and its larvae, fingerlings, small fishes, tadpoles, frogs, etc.

Clarias batrachus

Siluriformes

Omnivorous

Insects, worms, crustaceans, fish fry, insects larvae, decaying organic maters, etc.

Heteropneustes fossilis

Siluriformes

Omnivorous

Insects, worms, copepods, ostracods, debris, algae, etc

Labeo rohita

Cypriniformes

Herbivorous

Algae, microscopic plants, vegetable matters, detritus, sand and mud, etc.

Osphronemus goramy

Anabantiformes

Herbivorous

They mainly feed on aquatic plants and algae.

Oreochromis mossambicus

Cichliformes

Herbivorous

They mainly feed on aquatic plants and filamentous algae.

Ctenopharyngodon idella

Cypriniformes

Herbivorous

They voraciously feed on aquatic vegetation.

Hypopthalmicthys molitrix

Cypriniformes

Plankton feeder

Unicellular algae, rotifers, decaying microorganisms, detritus, etc.

Catla catla

Cypriniformes

Plankton feeder

Microscopic plants, Algae, rotifers, insects, crustaceans, etc.

Cirrhinus cirrhosus

Cypriniformes

Omnivorous

Algae, decaying plants, and animal matters, detritus and mud, etc.

Tor putitora

Cypriniformes

Omnivorous

Algae, decaying organic matter, insects, rotivers, protozoans, etc.

Tor tor

Omnivorous

Macro vegetation, filamentous algae, mollusks, sands and muds, etc.

Cyprinus carpio

Cypriniformes

Omnivorous

Algae, macro-vegetation, insects, rotifers, crustaceans, etc.

Concluding Remarks

Food and feeding pattern of fish is very important factor that helps to choose the fish type for cultivation. It helps to avoid clash for getting food among them in different water levels. Fishes are carnivorous, herbivorous or omnivorous however a large portion of them are exceptionally adaptable in their feeding habits and use the promptly available diet. Just a few fish groups are strictly herbivorous or carnivorous and the available food helps to decide if it will be eaten by the fish.

Fish Food and Types: Natural and Supplementary Food

Fishes are cold-blooded vertebrate aquatic animals. They prefer to feed various types of food due to their different food and feeding habits. Among them, some feed on plant-based food and some like to eat animal-based foods while many fish species take both plants and animals based food and they are known as omnivorous.

Some fishes only prefer food as phytoplankton and zooplankton and called plankton feeders. The most important zooplankton are various types of protozoans, crustaceans, rotifers, microscopic invertebrates, insect larvae, fish eggs, etc.

Fishes also feed on comparatively larger animals such as different oligochaetes, mollusks, small-sized fishes, tadpole and frogs. Many plant materials are also consumed by fishes including different types of algae (both unicellular and filamentous), some feed on portions of higher aquatic plants such as Azola, water hyacinth, Hydrilla, Spirogyra, etc.

Besides these, some fish species also take a very small amount of sand and mud with their other foods.

Food Types

Fish food can be divided into two main types:

  1. Natural food and
  2. Supplementary food or artificial food.

Natural Fish Food

Different types of food are produced naturally in ponds or reservoirs. These are called natural foods. They are very small and their movements depend on the direction of the water current that helps goes towards them. They are known as plankton. Plankton can be seen in all types of reservoirs, except for high flowing rivers.

Plankton is one of the small flora and fauna whose movement capacity is so limited that they cannot cross the stream. Therefore, in most aquatic environments, movements of a large number of plankton species are controlled by wave and water currents.

Most plankton (phytoplankton and zooplankton) can control vertical expansion through a slight movement. Some animal plankton or zooplankton can be more active and move more distances than their microbial bodies. However, their size is so small that their movement is greatly controlled through the water current or wave. This type of plankton is called nektoplankton.

Plankton are of two the following types:

  1. Phytoplankton
  2. Zooplankton

Phytoplankton

Phytoplankton are the autotrophic organisms that play a key role as the natural food of various fish species. Most of the phytoplankton are not seen by the naked eye due to their microscopic structure. But when present in large enough, they produce colored patches on the water surface because of the presence of chlorophyll, phycobiliproteins or xanthophylls in their cells.

Phytoplankton form about one percent of the global biomass. The watercolor becomes green to yellow or green to brown due to the presence of plankton. They are the ideal food for fish.

Green Algae

They are a portion of very popular fish food. Their main feature is the presence of chlorophyll or green particles in the body. Sometimes water surface is covered by a layer due to the abundance of such green algae and afterward, the water is polluted.

Among the various green algae, Chlorella, Chlamydomonas, Eudorina, Volvox, Scenedesmus, and Ulothrix are notable. These kinds of algae do not live for a long time. Overall, they are regulated when fertilizer and supplementary foods are stopped.

Blue-Green Algae

They are also plant-like microscopic organisms that grow in water bodies such as ponds, rivers, lakes, and streams. They are blue-green but can also be olive-green or red in color. They also play important fish food while alive and dead. Blue-green algae do not normally visible in the water, but their populations can increase rapidly to form a large mass or scum, known as bloom.

The bloom can cause harm to fish because they prevent sunlight into water bodies and make the depletion of oxygen level. The bloom commonly occurs during the summer months and when they form dense blooms then they make the water look bluish-green color.

Generally, if nutrients like phosphorus and nitrogen are available in the water that contributes to the growth of the blue-green algae. The algal bloom can also occur due to agricultural and stormwater runoff and leaching from septic systems.

Harmful Effects of Algal Bloom

  • If the large numbers of algae grow in the water body they consume a lot of oxygen at night and the water body becomes an oxygen-free state. As a result, fish die due to a lack of oxygen. In addition, the plants also die and fall into the water and reduce oxygen in the water.
  • If the growth of algae is high, two layers are formed on the water surface. Temperature and oxygen content greatly vary in these two levels which is harmful to fish. Temperatures and oxygen levels are higher in the upper layers of the water, while the temperatures and oxygen in the lower levels are very low. In this case, the sunlight cannot reach the bottom of the water body because of the layer of algal blooms.
  • The pH of water also increases abnormally during the day time due to the abundance of algae.
  • Besides, different blue-green algae such as Oscillatoria, Microsystis, etc. release toxin in the water which inhibits the growth of different zooplankton such as Daphnia, Cyclops, Diaptomus, Bosmina as well as fish.

Preventing Measures of Algal Bloom

The following simple steps should be taken to prevent the growth of blue-green algae:

  • Using phosphate-free detergents, and household cleaning products.
  • You can also prevent it by providing personal care.
  • By stopping or minimizing the application of fertilizers that contain phosphorus.
  • Preventing agricultural runoff by making plantation along the waterways.
  • Making reconstruction of natural shoreline on the lake and other water bodies.
  • By confirming or checking the septic system that does not leak into the water source.

Zooplankton

All kinds of animal plankton are known as 'zooplankton'. Zooplankton are one kind of heterotrophic organisms. They mainly feed on phytoplankton but some are detritivorous. Their body size range from microscopic to large-sized such as jellyfish which are visible in the naked eye.

They inhabit different types of water bodies such as the freshwater system and oceans. Zooplankton are the ecologically important organisms that maintain the essential constituent of the food chain.

They are larger than phytoplankton. When many numbers of zooplankton are raised in the water bodies, the watercolor is gray or light brown or light black.

They are the main food of fish larvae and fingerlings. Among zooplankton, some types of lower animals are available in the reservoir, known as rotifers. These are the favorite fish food.

Supplementary or Artificial Fish Foods

When we cultivate fish in large quantities and raise them, then it will not depend only on natural food. They have to provide supplementary or artificial foods made from outside. Besides, if we depend only on natural foods, they can disrupt the entire nutrition of fish.

In addition, organic and inorganic fertilizers are also needed in connection with a fish meal in the water body to produce the right amount of natural food. In this case, we can provide organic fertilizers such as cow dung, compost, earthworm, various types of sugarcane products and inorganic fertilizers like ammonium sulfate, urea, single super phosphate(SSP), murate of potash(MP) and so on which influence the growth of natural foods such as plankton (phytoplankton and zooplankton).

We can also provide lime regularly into the water body that enhances the health of fish, purity of water and ability to make fish food. Besides these, about ten types of amino-acids are needed in the nutrition for cultivated fish. These amino acids are called essential amino acids. These include:

  1. Arginine,
  2. Histidine,
  3. Isoleucine,
  4. Lucine,
  5. Lysine,
  6. Methionine,
  7. Tryptophan,
  8. Phenylalanine,
  9. Threonine and
  10. Valine.

In the supplementary diet, the required amino-acids should be at the appropriate levels. Fish food should contain 35% of protein levels. Carbohydrates are also very important nutrient components for fish. This carbohydrate generates the energy of the fish body.

Fish can store additional carbohydrates in the liver in the form of glycogen or stored in the body's muscle and when needed, they can use it. About 4 kilocalories of energy are found in almost every gram of carbohydrates.

The supplementary diet of fish should contain 1o.5 percent carbohydrates. In addition to carbohydrates, fish need to be fat for nutrition. Food should contain 4-8 percent fat. Essential fats like tocopherol should be present in the diet of fish.

Besides, protein, carbohydrates and fats, the body of the fish requires various nutrients such as minerals like calcium(Ca), phosphorus(P), potassium(K), chloride(Cl), magnesium(Mg), zinc(Zn), copper(Cu), iodine(I), iron(Fe), etc.

To make a balanced diet vitamin should be added to the supplementary food. In this case, different types of vitamins such as Vitamin A, Vitamin B (riboflavin, pyridoxine, niacin), Vitamin E Vitamin D and Vitamin K are the most important.

Supplemental food of fish is also made using animal-based ingredients such as fish powder, silkworm pupa, animal, slaughterhouse meat and blood, etc. Plant-based ingredients such as mustard oil cake, coconut cake, soybean meal, rice bran, wheat flour, wheat bran, etc are also used to make fish food.

Features of Supplementary Food

The availability and low cost of plant-based foods such as rice grain, rice bran, etc are usually used to make supplementary food in combination with mustard oil cake, or groundnut cake. They also reduce the cost of production. The price of coconut cake is relatively high, so the use of mustard oil cake is more prevalent.

Artificial Feed Selection Criteria for Fish

  • Ingredients for artificial foods should be cheap and locally available.
  • Palatable feed ingredients should be selected so that fish can be easily accepted due to its palatability.
  • You should use such types of ingredients that help to increase the fish yield so that you can earn extra money by selling your fish.

Different Feed Ingredients and Their Nutritious Value

Feed ingredients

Protein (%)

Lipid (%)

Fibre (%)

Rice corn

8-10

12-16

10-15

Rice bran

12-16

1-2

15-20

Maize grain

9-11

4-6

2-3

Barley

8-10

2-3

4-6

Coconut cake

23-25

12-14

10-12

Groundnut cake

40-45

4-10

6-8

Mustard oil cake

30-35

4-6

6-10

Soybean oil cake

36-40

5-6

4-6

Sunflower oil cake

28-32

4-6

10-12

Fish meal

50-65

8-12

2-3

Mussel meat

30-40

8-10

4-6

Shrimp meal

28-30

8-10

6-10

Silkworm meal

60-65

18-20

3-5

Concluding Remarks

The modern science-based fish farming system mainly depends on nutritious artificial or supplementary food that should give directly from the outside. Because natural food produced in the water body as a result of fertilizer application is not sufficient for the rapid growth of fish. Therefore, for the rapid growth of fish and the significant increase in the yield of fish, nowadays, various nutrient-rich artificial or supplementary feeds should be offered to the fish as the supplement of the natural food of fish.

Sixspine Butterfly Fish: Parachaetodon ocellatus

Sixspine butterfly fish is a very attractive fish which is also known as Ocellated Coralfish, Eye-spot Butterflyfish, Six-spined Butterfly-fish or Six-spined Coralfish. It has compressed, sub-rhomboidal body with prominent snout. Anterior portions of soft dorsal and anal fins are the highest. Lateral line ceases the opposite of the posterior fourth of the dorsal fin. 

Systematic Position

  • Class: Actinopterygii
  • Order: Perciformes
  • Family: Chaetodontidae
  • Genus: Parachaetodon
  • Species: Parachaetodon ocellatus

The fish has a white-brown color with five vertical brown bands. The first band runs through the eye which is orange in color with black edges. The fourth band with a black white-edged ocellus or eye like spot is present on base of the soft dorsal fin. The fifth band is over the free portion of the tail. It can reach up to 18 cm (7.1 inches) in length at adult stage.

It inhabits sand or silty bottom on coral reefs. Juveniles do not form schools but adult forms school with large numbers over open muddy substrates in deep water region. They are omnivorous fish and feed on benthos and coral associated invertebrates.

They are Indo-Pacific fauna and available in Red Sea, Arabian Sea, Bay of Bengal, Andaman Sea, Gulf of Thailand and seas around Malaysia and Indonesia including India, Sri Lanka and Bangladesh.

Globally this fish has no fisheries interest as food fish. However, as aquarium fish its demand is increasing day by day.

Quick Stats

  1. Scientific Name: Parachaetodon ocellatus
  2. Common Name: Ocellated coralfish, Eye-spot Butterflyfish, Six-spined Butterfly-fish or Six-spined Coralfish
  3. Minimum Tank Size: 75 gallons
  4. Temperament: Peaceful
  5. Adult size: 18 cm
  6. Diet: Omnivore
  7. Coral Safe: Yes
  8. Tank-mates: Peaceful or non-aggressive fish
  9. Temperature Range: 72 - 82°F (22 – 27°C)
  10. Specific Gravity: 1.020-1.026
  11. pH: 8.0 - 8.5
  12. Care Level: Moderate

Chondrichthyes Vs Osteichthyes:General Characteristics and Differences

There are approximately 34,000 known fish species throughout the world which live in either fresh or saltwater environments. They are cold-blooded animals but only the opah (Lampris guttatus) is warm-blooded fish which is also known as cravo, kingfish, moonfish, and Jerusalem haddock.  There are two main groups of fish, namely Chondrichthyes and Osteichthyes based on the composition of the endoskeleton. The endoskeleton of Chondrichthyes is made up of cartilages and they mainly live in marine habitats while the endoskeleton of Osteichthyes is composed of bones which are found in both marine and freshwater habitats.

Chondrichthyes

It is a diverse group which contains more than 700 species, found throughout the world's marine environments. This group includes the sharks, rays, and skates, and their skeleton is made up by rubbery cartilage, which is very light and flexible. The world`s largest member of Chondrichthyes is the plankton-feeding whale sharks (Rhincodon typus)  which can grow up to 18 meters (60 feet) in length with 21.5 tonnes in weight and live up to 130 years. The main characteristics of chondrichthyans fish include jaws, paired fins, paired nostrils, placoid scales, and two-chambered hearts.

image of Whale-shark

whale sharks (Rhincodon typus)

General Characteristics of Chondrichthyes

  • The body is covered by tough skin with minute placoid scale and mucous glands.
  • They have jaws and paired appendages.
  • They lack the air-filled swim bladder.
  • They have median and paired fins which are supported by cartilaginous fin rays.
  • The mouth is ventrally placed with rows of teeth.
  • They have heterocercal type caudal fin.
  • They have a well-developed electroreceptive system.
  • They have 5-7 pairs of gills for performing respiration with no operculum.
  • The male members of Chondrichthyes have specialized paired intromittent organs or reproductive organs at the inner edge of the pelvic fins which is known as clasper.
  • They may be oviparous (egg layers), viviparous (live-bearer) or some species are ovoviviparous (mother carry eggs in her body).
  • They produce large-sized yolky eggs and their fertilization is internal with direct development.
  • The digestive system consists of a j-shaped stomach and short intestine with a spiral valve.
  • The fish bears one or two nostrils which never opens in the mouth cavity.
  • The heart bears a contractile conus arteriosus with rows of valves.
  • They have typically paired gonads and gonoducts which open into the cloaca.
  • Most Chondrichthyes exhibit a massive growth with up to 21.5 tonnes in weight (whale shark).
image of Heterocercal-tail

Heterocercal tail

The class Chondrichthyes is divided into the following two subclasses:
  • Subclass-1: Elasmobranchii (sharks, rays, skates, and sawfish) and
  • Subclass-2:  Holocephali (chimaeras)

Characteristics of subclass Elasmobranchii

  • The members of the Elasmobranchii have no swim bladders.
  • They have 5-7 pairs of gill clefts which open individually to the exterior.
  • They have a rigid type of dorsal fins.
  • The body is covered with small placoid scales.
  • A tapetum lucidum tissue layer is present in the eyes.
  • The male members bear reproductive organs at the inner edge of each pelvic fin for the transmission of sperm which is known as clasper. 

Examples:  Sharks, rays, and skates.

Characteristics of Subclass Holocephali

  • They have a cartilaginous skeleton with high compressed head and small narrow mouth which gives the head a parrot-like appearance.
  • They have a thin and long tail with large pectoral fins.
  • The front side of the dorsal fin bears an erectile spine.
  • They have simplified gut with no stomach where the stomach is merged with the intestine.
  • The gill clefts are covered by a fold of skin.
  • In nature, they inhabit close to the bottom and their foods mainly consist of mollusks and other invertebrates.

Examples: Rat fishes (Chimaera), rabbit-fishes (Hydrolagus) and elephant-fishes (Callorhynchus).

Osteichthyes

It is the largest class of subphylum Vertebrata which contains approximately 28,000 known species that comprise 96% of all fishes. At the embryonic stage, the endoskeleton is cartilaginous but in the adult stage, endoskeleton is replaced by a bony skeleton. They live in both marine and freshwater environments. The largest bony fish is the ocean sunfish or common mola (Mola mola) in the world, which grows up to 2.3 meters in length and 2300 kg in weight while the smallest fish is the dwarf pygmy goby (Pandaka pygmaea) which can grow up to 9 mm (female) and 15 mm (male) in length. Class Osteichthyes has two groups: ray-finned and lobe-finned fish where the ray-finned fish bears a single dorsal fin while lobe-finned fish bears two dorsal fins.

image of Dwarf-pygmy-goby

Dwarf pygmy goby (Pandaka pygmaea)

General Characteristics of Osteichthyes

  • The body is rounded and tapered at the ends (fusiform body).
  • They bear paired (pectoral and pelvic fins) and unpaired fins (dorsal, anal, and tail fins).
  • The endoskeleton is made up of bones.
  • They are found in either marine or freshwater habitats.
  • The caudal or tail fin is homocercal type.
  • They have 4 pairs of gills or breathing organs which are covered by the gill covers or the operculum on each side.
  • They have sac-like outgrowth which is known as swim bladder or air bladder that also acts as a hydrostatic organ. It arises from the dorsal wall of the esophagus which is used to maintain balance and to swim up and down.
  • The exoskeleton is dermal in origin if present which is composed of cycloid, ctenoid or ganoid scales
  • They possess a terminal mouth which is located at the anterior tip of the body.
  • They have well developed lateral line system which runs through the body and consists of a series of sensory organs, called neuromasts that help to sense both water pressure and vibrations.
  • Digestive tract leads into the anus with no cloaca.
  • They have well-developed eyes with the nictitating membrane.
  • Generally, their fertilization is external with direct development. Most of the fishes are oviparous but some are ovoviviparous.
image of Homocercal-tail

Homocercal tail

Examples: Cyprinids, Perches, flying fish, globefish, sea horses and eels, etc.

Living Osteichthyes are divided into the following three subclasses:
  • Subclass-1: Dipnoi
  • Subclass-2: Crossopterygii, and
  • Subclass-3: Actinopterygii.

Characteristics of subclass Dipnoi

  • This subclass contains 6 extant species under two orders: Ceratodontiforms and Lepidosireniformes.
  • They are also known as lungfishes.
  • The largest lungfish is the African lungfish which can reach up to 2 m (6.6 ft) in length and 50 kg (110 lb) in weight.
  • They have an air-breathing organ which opens to the esophagus.
  • They have long and tubular pelvic and pectoral fins.
  • Its dorsal and anal fins are fused with caudal fin.
  • The upper jaw is fused to the braincase with fused teeth.
  • They are omnivorous and their foods consist of fish, insects, worms,  crustaceans,  mollusks, amphibians and plant matter, etc.
  • Their digestive tract contains an intestinal spiral valve.

Examples: Australian lungfish  (Neoceratodus forsteri) South American lungfish (Lepidosiren paradoxa),  West African lungfish (Protopterus annectens), etc,

image of Australian-lungfish

Australian lungfish

Characteristics of subclass- Crossopterygii

  • They are also known as lobe-fined fishes.
  • They have typically paired fins which act as support against the floor of the water body.
  • All fins have movable lobes or stalks.
  • The caudal fin is either diphycercal or heterocercal types.
  • They have two dorsal fins with separate bases.
  • The largest member of this subclass is the West Indian Ocean coelacanth which can grow up to 2 m (6 ft 7 in) in length and 110 kg (240 lb) in weight.
image of Coelocanth

Coelocanth

Subclass-Actinopterygii

The members of the subclass Actinopterygii are known as ray-finned fishes. They are the most diverse and the largest group of fishes with a wide variety of shapes, sizes, and colors which comprises half of all the living vertebrates. There are approximately 24,000 known species under 42 orders with 431 families. Among them, Teleosts comprise approximately 23,000 species and 96% of all living fish species. 

Characteristics of subclass Actinopterygii

  • The fins are supported by rays or spines which give the name ‘actinopterygians'.
  • The unique features of the ray-finned fish is the swim bladder which helps them to move up or down in the water body.
  • The gills are covered by an operculum and the fish perform respiration through gills.
  • They inhabit a variety of environments such as marine and freshwater within 1 to 7000 m depth ranges.
  • They have different types of scales such as ganoid and laptoid scales (cycloid and ctenoid).
  • They have branchiostegal rays which are originated from the bones at the base of the branchial cavity.
  • They have homocercal tail fin where the upper and lower lobes are the same length.

Examples: The most familiar fish species of Actinopterygii includes, sturgeons, anchovies,  gars, eels, bass, carp, herrings, cichlids, catfishes, oarfish, goldfishes, pickerel, piranhas,  seahorses,  salmon, trout, etc.

image of seahorse

Seahorse

Difference Between Chondrichthyes and Osteichthyes

Key Features

Chondrichthyes

Osteichthyes

Common names

They are also known as cartilaginous fishes.

They are also known as bony fishes.

Habitat

They inhabit in the marine environment. Sometimes many cartilaginous fishes enter into freshwater environments.

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They inhabit in both marine and freshwater environments

Endoskeleton

Endoskeleton is made up by the cartilage.

Endoskeleton is made up by bones.

Scale types

The body is covered by very small denticles, known as placoid scales.

If present, scales are various types such as ganoid and laptoid scales (cycloid  and ctenoid).

Generally, they have a  large-sized body.

Comparatively, they are small-sized fish.

Mouth position

They have ventrally situated mouth.

Their mouth is located at the anterior tip of the body. This type of mouth is known as terminal mouth.

Numbers of Gills

They have 5-7 pairs of gills.

They have 4 pairs of gills.

Gill cover or operculum

The gills are not covered by gill cover or operculum. 

The gills are covered by an operculum on each side.

Swim bladder

They do not have swim bladders.

They have swim bladder for buoyancy. It is also known as air bladder or gas bladder.

Caudal fin

They have heterocercal type caudal fin.  In this case, lobes are not equal.

They have homocercal type caudal or tail fin. In this case, both lobes are equal in size.

Fertilization

In many cases, internal fertilization occurs.

In most cases, external fertilization occurs.

Excretory products

Their excretory products are urea (CH4N2O)

Their excretory products are mainly ammonia (NH3).

Feeding behavior

Generally, they are carnivores in nature.

They may be omnivores, carnivores, herbivores, filter-feeders or detritivores.

Examples

Skates, sharks, and rays.

Tuna, Dolphin fish, Barramundi, Salmon fish, trout, rohu, seahorse, etc.

image of Different-types-of-scales

Different types of scales

Concluding Remarks

Fish are the cold-blooded aquatic organisms which belong to the subphylum Vertebrata of phylum Chordata. There are two main groups of fish based on the endoskeleton, namely Chondrichthyes and Osteichthyes. The endoskeleton of the members of Chondrichthyes is made up of cartilage while the endoskeleton of fish under the class Osteichthyes is composed of bones. Fish are very important to human beings because they provide nutrients and micronutrients. These nutrients are essential for the physical development of children. It is also an important part of a healthy diet of all stages of people and controls many diseases. They are an important source of income and employment for the people of many developing countries.  At present, 1245 (8.1%) fish species are listed as vulnerable (IUCN). Among them, 121 species belong to the cartilaginous fish and 1114 species are ray-finned fish. Fish become vulnerable due to pollution, habitat destruction, diseases, over-exploitation, etc.  To protect our fish species, we should take proper conservation measures.

Fish: Size Variations, Appearance and Its Body Parts

Fish are cold-blooded aquatic vertebrate animals with torpedo shaped body. They have a wide variety of shapes, colors, and sizes. There are approximately 34,000 species of fish in the fresh and salt waters of the world.

Size Variations

There are numerous living fish species in the world. Among them, many fish are under a few cms in length at the adult stage. Dwarf pygmy goby (Pandaka pygmaea) is the smallest fish, of which, an adult male can grow up to 15 mm in length and adult female grows up to only 9 mm in length. But some fish species can grow tremendous sizes. Oarfish (Regalecus glesne) is the longest bony fish in the world which can reach up to 36 ft. (11 m) in length.

Some notable fish species and their length and weight are given in the following table

NAME OF FISH

SCIENTIFIC NAME

LENGTH

WEIGHT

WEIGHT

Common ocean sunfish

Mola mola

up to 10.8 ft (3.3 m)

up to 2,300 kg

All warm and temperate seas

Beluga sturgeon

Huso huso

up to 5 m (16.4 ft.)

up to 2,000 kg

The Caspian, Black, and Adriatic Seas

Black marlin

Makaira indica

up to 15.4 ft (4.7 m)

up to 750 kg

South California to the Gulf of California to Chile.

European wels catfish

Silurus glanis

up to 16.4 ft.(5 m)

Up to 300 kg

Caspian and Aral Sea basins

The Appearance of the Body

The body shape of the bony fishes shows huge varieties. The typical fishes such as perches and basses have a compressed body, flattened from side to side. In others, such as carps and minnows, the body shape is elongated, usually with a rounded belly. In flatfishes like the soles and flounders, the body is depressed from top to bottom, while the other forms like the eels have an elongated and snake-like body.

Generally, fish show body shape in three ways: elongation, compression, and depression.  A laterally compressed body shape is more common in bony fishes which dwell within coral reefs such as Butterflyfishes (Chaetodontidae) while depressed body shape is found in bottom-dwelling fishes such as Goosefishes (Lophidae) and batfishes (Ogcocephalidae). The elongated body shape is found in eels like the morays (Muraenidae).

image of Body parts of fish

Body Parts of Fish

The shape of the Head

The size of the head may be large, moderate and small. The head is covered on both sides by several bones such as the preopercle, opercle, interopercle and subopercle which together form the gill cover. Other parts of the head include the nostril, eye, chin, cheek, branchiostegal ray etc. The anterior part in the upper jaw of fish is known as premaxilla, the posterior one is known as maxilla while the lower jaw is known as mandible..

Scales

The body of the most bony fishes is covered with a layer of plates which are known as scales. It also acts as protected layers against predators. But some bony fishes may have scales only on portions of their body, and some species have no scales. The body of the most bony fishes is covered with cycloid or ctenoid scales.

Most bony fishes such as perches, basses, etc have tough, shingle-like scales with a comb-like or serrated edge along their rear margin, known as the ctenoid scale. Others fish like carps, barbs; minnows, etc have rounded scales with smooth edges along the rear margin, known as cycloid scale. Cycloid scales are smooth and circular in shape and they overlap the body from head to tail.

An outer layer of both cycloid and ctenoid scales consist of calcium and an inner layer of connective tissue. A characteristic toothed edge is present on the ctenoid scale. They are most common on fishes which have spiny fin rays. Scales of some fishes such as gars (family Lepisosteidae), bichirs, and reedfishes (family Polypteridae), are hard almost bony, fitting one against the other like the bricks on a wall. These are called ganoid scales. It has a layer of ganoin which is a hard, enamel-like substance. Ganoid scales are diamond-shaped, shiny, and hard. Some fishes do not have scales at all such as catfishes. Scales of the eels are widely separated and buried deep in the skin.

The placoid scale consists of a hard base embedded in the skin with a spiny process known as cusp and is a characteristics feature of the sharks.

image of cycloid scale

Cycloid Scale

image of ctenoid scale

Ctenoid Scale

image of Ganoid scale

Ganoid Scale

image of Placoid scale

Placoid Scale

Different types of fish scales

Body Spines and Rays

Some scales are modified to form body spines. Most of the bony fish have spines or rays. Generally, spines are inflexible, sharp and un-segmented while rays are flexible, segmented, and soft. Rays may be branched. The fish fin may contain only soft rays or only spiny rays or a combination of both. If fin contains both spiny rays and soft rays, the spiny rays are always located at the anterior position of the fin.

Generally, spines have various functions. In catfish, pectoral or dorsal fin bears spine which is used as a form of defense.  Razor-sharp and mobile pre-caudal fin spines are found in most surgeonfishes (Acanthuridae) that they use it to protect themselves against predators.  Some bony fishes such as pufferfishes (Tetraodontidae) have spines which cover the entire body to protect themselves against predators.

Fins

Fins are the most distinguishable characteristics of fish which help to identify the fish species. It is a thin component which composes of bony spines protruding from the body skin. Fins are located in different places of the body for serving various purposes. Swimming is the general function of fins.  In fishes, fins are the following types:

Dorsal fins: This type of fin is located on the back of the fish. The fish uses it for locomotion and making a balance in the water during swimming. It also helps to defend the fish against rolling.

Caudal fins: It is also known as tail fin which is located at the end of the caudal peduncle. It is mainly used for forwarding movements. Caudal fins are of different types such as:

image of fish fin

Fish Showing Different Types of Fins

  • Heterocercal: Found in sharks
  • Protocercal:  Found in cyclostomes and the living dipnoanst
  • Diphycercal: Found in bichir, lamprey, coelacanth, and lungfish
  • Homocercal: Found in most modern fishes. These types of fins have a variety of shapes such as:
  • Rounded
  • Truncated
  • Forked
  • Emerginate
  • Lunate
  • Double emerginate
image of Caudal fin types

Caudal Fin Shapes

Anal fin: It is positioned on the ventral (bottom) surface of the fish body just behind the anus. Fish use it for stability during swimming.

Pectoral fin: It is placed near the operculum on each side of the body homologous to the human arms.

Pelvic fin: It is a paired fin which is placed the ventral surface of the fish body homologous to the hind limbs of tetrapods.  This type of fin makes force during swimming for going up and down in the water.

Adipose fin: It is a soft and fleshy type fish which is located behind the dorsal fin closer to the caudal fin. This type of fin helps the fish during navigation in rough water.

Mouth and its Position

The mouth has a different size and shapes. The position of the mouth varies in different species. A mouth opening straight with the snout projecting in front is known as terminal mouth. A mouth posterior to the tip of the snout is known as sub-terminal. A mouth positioned on the underside of the head with the snout projecting in front is known as inferior. A mouth that opens upward, with lower jaw more anterior than upper jaw is known as superior. Oblique mouths are characterized by the angle of the closed mouth which is about 45 0 or more when closed. Protracted mouths are those that are protrusible and are directed upwards or downwards. A ventral mouth is located entirely on the ventral side of the head.

The shape and size of the mouth is the good indicator of feeding habits of bony fishes. Generally, mouths of most of the bony fishes are positioned at the frontage end of the head.  Mouths of some bottom-dwelling fishes are located on the underside position of the snout that is angled toward the bottom while some surface-feeding fishes have mouths that can angle upwards. The mouth of butterflyfishes (family Chaetodontidae) is small with thin snouts which are used for searching food in crevices and cracks. Some bony fishes have barbells around the mouth which help to detect food. 

image of Inferior mouth

Inferior Mouth

image of Superior mouth

Superior Mouth

image of potrusible mouth

Potrusible Mouth

image of Terminal mouth

Terminal Mouth

Image Showing Different Types of Mouth of Fish

Teeth

Tremendous diversity exists in the form and size of fish teeth. The character of dentition is dependent on the feeding habits of the fish. Some fishes have pointed-edged wounding teeth called incisors located in the forward part of the mouth. Some species possess sharp conical teeth known as canines. Many species have molariform teeth that can easily crunch organisms like mollusks, crustaceans, and other animals. Some fishes have villiform teeth that are slender and form velvety bands. Fishes like carps, minnows, and suckers have teeth in their throat. These teeth are known as pharyngeal teeth and are sharp in some, molariform in others. Some fishes have teeth on the roof of the mouth.

Image of Canine teeth

Canine teeth

image of Inscisor teeth

Incisor teeth 

image of Molar teeth

Molar teeth

Different types of teeth of fish

Finlets

Finlets are modified small fins which look like ridges and they are located between the dorsal and the caudal fin or between the anal and the caudal fins. They are found in very fast swimming fish like tuna. It helps to increase the swimming speed of the fish, by cutting through the water.

image of finlets

Image Showing Finlets

Scutes

Scutes are enlarged bony dermal plates or scales usually associated with the lateral line or on the caudal peduncle or along with the ventral profile. Fishes of the family Clupeidae have a series of scutes along the abdomen. Generally, scales are modified and form sharp, protective plates or scutes. It acts as a body armor environmental abrasions and even predation.

Generally, scales on the caudal peduncle form scutes. Some fishes such as Jacks mackerel have a row of scutes along the lateral line on either side but an abdominal row of scutes are present on River herrings and threadfins. Body of the pinecone fish (Family Monocentridae) is completely or partially covered with scutes.

image of scutes

Fish Showing Scutes

Fish Fins: Types, Modification and Functions

Fins are one of the most distinguishing features of a fish and they have several different forms. Two types of fins are found in most of the fish: median and paired fins. Median fins are single in number which runs down the mid-line of the body. In fishes, median fins are dorsal, caudal and anal fins while paired fins are pectoral and pelvic which are arranged in pairs homologous to human arms and legs. Fins help to swim and maintain the balance of the body. Fins also help to identify the fish species. Different types of median and paired fins are described below:

image of fish fins

Fish showing different types of fins

Dorsal Fin

This type of fin is located on the top or back of the fish which help the fish in quick turns or stops. It also helps the fish against rolling.  In fish, there are three distinct dorsal fins such as proximal, central or middle, and distal dorsal fins. Some fish have two dorsal fins where the central and distal fins are combined together.

The Types of Dorsal Fins

  • Single
  • Pointed
  • Split
  • Spine triangular
  • Trigger
  • Trailing

Pelvic Fin

In fishes, a pair of pelvic fins are present which are located ventrally below and behind the pectoral fins. In some fishes, they are situated in front of the pectoral fins (Cod family).  This type of fin helps in stability and slowing down the fish. Generally, fish use pelvic fins for moving upwards and downwards in the water.

Anal Fin

The Anal fin is also known as cloacal fin which is located on the ventral side just behind the anus. It supports the dorsal fin and stabilizes the fish during swimming and contrinols the rolling motion.

Pectoral Fin

Pectoral fins are located on both sides usually just behind the operculum. It is homologous to the tetrapod`s forelimbs. It provides supports during swimming. It creates dynamic lifting force and also helps the fish to turn left or right.

Adipose Fin

They are soft fins and located between the dorsal and caudal fins, usually very near to the caudal fin. It is mainly found in Salmonidae, Characins, and catfishes. This type of fin help to navigate the fish in rough water.

Caudal Fin

The caudal fin is the primary appendage which is used for locomotion in many fishes. The caudal fin is also known as tail fin or a median fin which is usually homocercal or heterocercal. Generally, it is a vertically expanded structure which is located at the caudal end of the body. The base of the caudal fin is known as caudal peduncle with strong swimming muscles.  In general, caudal fin acts like a propeller while the caudal peduncle functions as a motor.

The caudal fin has two lobes such as dorsal epichordal and ventral hypochordal lobe which are supported by the modified last three caudal vertebrae. The shape of the caudal fin may vary in different species from rounded to pointed, notched, emarginated, truncated, etc. It is used to identify the fish species. Generally, fish use it for forwarding propulsion and speed.

The caudal fin of the adult fishes may be grouped into three categories:

1. Protocercal Caudal Fin

It is the most primitive type of caudal fin where the straight vertebral column divides the caudal fin into two equal lobes such as upper lobe and lower lobe. In this case, the upper lobe is known as epichordal or epicaudal and the lower lobe is called hypochordal or hypocaudal lobe. A series of rods are arranged around the central axis of the caudal region, which support the fin membrane. Undoubtedly, during the developmental period, the caudal fin of all fishes passes through the protocercal stage. This type of fin is found in cyclostomes and the living dipnoans(lungfishes).

2. Heterocercal Caudal Fin

The heterocercal tail is sometimes called the shark-tail type of caudal fin.Elasmobranch (cartilaginous fish) and some primitive type of bony fishes contain this type of fin.  This fin has two unequal lobes where the upper smaller lobe is known as epichordal lobe and a much larger lower lobe is known as hypochordal lobe. In this case, the hind end of the vertebral column becomes bent upwards and continues almost up to the tip of the fin.

3. Homocercal Caudal Fin

Most of the higher teleosts have homocercal caudal fin. It has superficially symmetrical and two equal sized lobes such as upper epichordal and the lower hypochordal lobe. Internally, this tail is asymmetrical and the hinder end part of the vertebral column is greatly shortened and turned upward.  In this case, the vertebral column does not touch the posterior limit of the fin..

image of Different types of caudal fins

Different types of Caudal Fins

Varieties of Caudal Fins

The internal and external structure of caudal fin varies which depends on the swimming habits of the fish. Generally, these variations involve special modification of the vertebral column. Following seven main types of caudal fins are found in fishes:

  • Lunate or Crescentic: It is used for Continuous long distance swimming.  e.g. Tuna
  • Forked: It is used for rapid swimming, e.g. Herring, Mackeral.
  • Emarginate: e.g. Trout, Carp, Perch.
  • Truncate: It aids in turning quickly. e.g. Flounder
  • Rounded: It is used for slow swimming, accelerating, and maneuvering. e.g. Turbot and Lemon-Sole.
  • Pointed: e.g. Gobby
  • Double emarginate
image of Caudal fins shape

Caudal fins shapes

Modifications of Caudal Fin

Many fishes have specialized modified types of caudal fins such as:

  • Isocercal or leptocercal
  • Internally symmetrical Caudal Fin
  • Pseudocercal Caudal Fin
  • Hypocercal Caudal Fin
  • Gephyrocercal Caudal Fin
(1) Isocercal or Leptocercal

In some fishes, tapering and symmetrical types of fin is present which is known as isocercal or leptocercal caudal fin. In this case, the spine is long with a straight rod-like structure. Rat tails (Macruidae), Blennies (Blennidae) Eels (Anguilliformes), feather backs (Notopteridae), and Gymnarchids (Gymnarchidae), etc have the isocercal caudal fin. 

(2) Internally Symmetrical Caudal Fin

This is a reduced type of caudal fin where some fin elements are fused together. They are found in cods (Order: Gadiformes).

(3) Pseudocaudal Caudal Fin

In the modern lungfishes (Dipnoi), the pseudocaudal caudal fins are found. In this case, fins are developed from the backward growth of dorsal and ventral elements.

(4) Hypocercal Caudal Fin.

This type of caudal fin bears much larger dorsal lobe than the ventral lobe which is greatly reduced. They are found in certain early Agnathans. It is also known as inverted heterocercal caudal fin. In this case, the vertebral axis turns downwards sharply where the lobe develops from its upper surface. .

(5) Gephyrocercal Caudal Fin

It is a very specialized type of caudal fin which is also known as bridge caudal fin. Generally, they look like the isocercal fin but the fins are reduced to vestiges. In this case, the caudal lobe is truncated where hypurals of the spinal column are lacking. These types of fins are found in the pearlfishes (Carpus), Flerasfer and Orthagoriscus.

Functions of Fins

Fish use their fins for various purposes. Some important functions of fins are described below:  

  • Generally, the pectoral fins help a fish for turning.
  • Some bony fishes use their pectoral fins to help them rest on the bottom or on reef areas (e.g. Cirrhitichthys).
  • Mudskippers (Periophthalmidae family) use pectoral fins for supporting themselves on land.
  • Flying fish (Exocoetidae family) use their long pectoral fins for gliding over the water.
  • Pectoral fins of some bottom-residence fishes such as threadfins (Polynemidae) bear touch receptors and taste buds which help to trace food.
  • Pelvic fins help the fish stability in the water.
  • Pelvic fins of some fishes such as clingfishes (family Gobiesocidae) use as sucking appendage, which helps a fish hold on to stationary objects on the ocean bottom.
  • Most of the bony fishes use their dorsal fin for sudden direction changes.
  • Dorsal fins act as a ‘keel’ for keeping the fish stable in the water.
  • Some angelfishes (Lophiiformes) use their dorsal fin as a lure which helps to attract the prey.
  • The modified dorsal fin of some fishes (Echeneidae) use as a sucking disc.
  • African knife fish (Gymnarchus niloticus) use its dorsal fin to move forward or backward by creating undulating.
  • Most of the bony fish use their caudal fins for propulsion.
  • Lunate caudal fins are characteristic features of fast swimmers such as tunas. They use it for maintaining rapid speed for long duration..
  • Anal fins make stability and anal fins of some bony fishes help in reproduction. 
  • Sea Robin fish use their pelvic fin for walking along the substrate.
  • Some fishes such as Freshwater butterflyfish (Pantodon buchholzi) use their pelvic fins for gliding.
  • Sea Robins use their pectoral fin for gliding around in the currents.
  • Lionfish and other scorpionfish have dorsal fins with hollow venomous spines which are used for self-defense.