Food is the essential components of life for every living thing in the living world. Every living thing, regardless of plant or animal, takes food from its own environment. So the nutrition of any animal depends on the intake of food and water. Animals consume food for three main purposes, namely:
(1) Food provides energy to control various biological functions in the body such as movement, muscle contraction and expansion, etc.
(2) Food is used as an essential ingredient for proper growth and repair of the body; and
(3) Food is the fuel that provides energy and maintains the body.
The essential nutrients of an animal are carbohydrates or sugars, proteins, fats, water, minerals, salts and vitamins. The first three elements are used to build energy and the body and the next three elements are used to control various functions of the body. Besides, various organic ingredients such as choline, sterol, purine, and pyrimidine are important for food.
Nutrition is an anaerobic process. In most animals, it is of the holozoic type. Nutritional methods include food swallowing, digestion, absorption and assimilation. To perform such functions, a mechanism known as the digestive system has developed in vertebrates. Most of the food changes and becomes simple and soluble so that it can be easily absorbed by the blood and lymph. Such mechanical and chemical breakdown or change in food is called digestion. The digestive system consists of the digestive tract and the associate digestive glands. It originates from the embryonic endoderm.
Fish Food
Like other animals, fish need food to grow and survive. The materials that a fish consumes for its growth, replenishment, energy production and reproduction is called fish food. Food plays an important role in fish breeding. Eating a balanced diet accelerates the growth of the fish and the fish reach sexual maturity in time. As a result, the reproductive glands of the fish are fully developed and the production of eggs and sperm is increased. Fish need a lot of energy for various important processes of life, such as blood circulation, respiratory management, hypertension control, suspension and submergence. Fish get this energy from taking food.
Types of Fish Food
There are different types of fish food in the water, such as dissolved nutrients and different types of plants and animals. Details about direct nutrient intake are not known, but some fish have been found to absorb glucose directly from water. There are many primary and secondary constituents and ions that are dissolved in water and taken to the digestive tract by the fish directly through the gills or with food.
Some fish absorb calcium ions through the alimentary canal to form fibers and bones. Similarly some amino acids are also absorbed. Different fish eat different types of food. Some fish eat only plant material while some fish depend on animals for food. Most fish take protein, carbohydrates, fats, vitamins, etc., and other ingredients from both plant and animal sources for their growth and well-being.
These fish foods come from two main sources, namely-
(1) The environment in which fish live, i.e. from the aquatic environment and
(2) Outside the aquatic environment i.e. from the land surface of the earth.
According to this difference in food sources, fish food can be mainly divided into two parts, viz.
(1) Natural food and
(2) Supplementary feed
1. Natural Food
Water is the medium of sustaining the life of fish. The foods that are naturally produced in the water of a reservoir are called natural fish food. Plankton, aquatic insects and plants, aphids, organic matter at the bottom of ponds, etc. are natural food for fish. Natural food is the main source of food for fish to survive. The adequacy of natural food in a reservoir depends on the initial productivity of that reservoir.
Sources of Natural Food
Almost all naturally occurring organisms in water, regardless of plant or animal, are natural food sources. Fish also consume non-living decaying matter at the bottom of the water and on the mud. These decaying organisms contain a large number of bacteria and protozoa which are more nutritious and important as natural food for fish. These natural foods of fish mainly interact with each other in such roles as hunters and predators and compete with each other for food, space etc. Such an interaction of organic matter is called food cycle. Natural food of fish in water body is produced through providing food.
The natural food of fish obtained in aquatic environment can be divided into the following 6 categories, viz
(A) Plankton: The tiny or microscopic animals and plants organisms present in water are called plankton. Plankton cannot swim against water waves or currents. They float passively in the rhythm of currents or waves. Plankton is the main natural food of fish. The presence of more plankton in the water indicates higher productivity of the reservoir. The color of the water appears green or brown indicates excess of plankton. Plankton is divided into plant plankton (phytoplankton) and animal plankton (Zooplankton).
(B) Periphyton: Periphyton are small plants and animals that cling to the branches of relatively large aquatic plants with roots or live firmly in a solid shelter at the bottom.
(C) Nekton: A relatively large aquatic animal that can swim freely and move freely is called a necton. Nectons can free themselves from being caught in plankton nets, such as the oyster beetle, aquatic insects, and so on.
(C) Neuston: A creature that swims or rests on the surface of the water or in a floating state is called a neuston such as insects.
(D) Benthos: An organism that lives on the surface of mud or in mud under water is called benthos such as snails, oysters, insect larvae, oligochaetes etc.
(E) Macrophytes: A relatively large aquatic plant is called a macrophyte such as Pistia,Hydrilla, Najas, Ceratophyllum, Wolffia, Lemna etc.
2. Supplementary Feed
In addition to providing natural food for higher production, some food is provided from outside the reservoir. These foods given from outside are called supplementary food. Rice husk, wheat bran, mustard oil cake, rice bran, etc. are supplementary food for fish.
In addition to the above categories, fish food can also be classified in the following ways, viz:
- Plants food
- Animal food
- Mixed food
- Prepared food
(1) Plant food: Foods that are obtained from plants or vegetable sources are called vegetable or plant food, such as phytoplankton, Azola, Pistia, green grass, soft aquatic plants, rice husk, corn husk, mustard oil cake, wheat bran etc.
(2) Animal food: Food obtained from animals or animal sources is called animal food, such as zooplankton, small aquatic insects, cattle blood, silkworms, fish meals, etc.
(3) Mixed food: Mixed food is the food made by mixing food of plant and animal or both sources together, such as rice husk, cattle blood, rotten organic matter at the bottom of the pond etc.
(5) Prepared food: The balanced food that is prepared by mixing different food ingredients together is called prepared food. Food is produced in the form of granules, pellets. There are different types of prepared food available in the market now. Such as- starter, grower etc.
Parasitic fish, especially marine lampreys (Petromyzon marinus), feed on the blood and tissue fluids of other fish. Many small fish start eating plankton while they are staying in the yolk sac using their small mouths. Some fish, especially the Gizard Sads (Dorosoma), have a number of long, densely packed gill rakers, so they eat mainly plankton throughout their lives.
Fish that have cutting teeth, they nip parts of plants such as leaves, stalks, grass etc (parrot fish – Asaridae, Surgeon fish – Acanthurus, freshwater tilapia – Oreochromis mossambicus and grasscarp – Ctenopharyngodon idella). In some cases, fish take body parts such as scale, skeleton, etc as food by other fish. In addition, Indian catfish (Schibeidae) and African cichlids take the scales of others as food (Lepidocaly). In addition, trout (Salmo, Salvelinus) can be seen eating small parts of the fins of other fish.
Different diet and food intake occurs in different species of fish. Nikolsky (1983) divided fish food into four categories, viz:
(1) Basic foods: Basic foods are the foods that most fish eat. It is usually included in most of the fish diet.
(2) Secondary foods: Sometimes fish consume small amounts of food which is related to the basic food elements. Such food forms the secondary food of fish.
(3) Incidental foods: An ingredient rarely enters the digestive tract and forms such food.
(4) Obligatory foods: All the foods that fish consume due to insufficiency of basic food in adverse conditions are known as compulsory foods.
Classification of Fishes
Based on Food Intake fishes are divided into different groups. The following classification shows the different types of fish:
1. Based on the characteristics of the food, fish are divided into the following four groups, viz
Plankton Feeders
Fish that feed on plankton (phytoplankton and zooplankton) are called plankton eaters. Most immature adult fish are usually plankton eater. However, some adult fish, such as the Peruvian encovi (Engaruls ringrens) and the Atlantic Menheaden (Bravoortla), rely more on phytoplankton than on zooplankton. They feed by sieving through large gill rakers or by mucus secreted from the epibranchial glands. In such filtration methods, zooplankton is seldom taken as food. Such eater eats zooplankton like fish larvae.
Herbivorous
This type of fish eats aquatic plants, flowers, fruits, seeds, leaves and young stems. They also eat algae that grow on rocks or pebbles by mouth using wide lips under their snout. Most of the herbivores live in the sea and are specially adapted to eating a variety of foods. Some sturgeon fish (Acanturidae), rabbit fish (Siganidae) and parrot fish (Scaridae) feed on the algae created on the rocks by grazing by their serrated teeth. Parrot fish use their beaks and rabbit fish use jaw-cutting nature structures.
Carnivorous
Carnivorous fish that eat things made from animals such as aquatic invertebrates and vertebratebts (fish larvae, fry and small fish mollusks, crustaceans) are called carnivorous fish. Such fish are usually predatory.
Omnivorous
Fish that feed on both plants and animals are called omnivorous fish.
2. Based on the variety of food choices, Nikolsky (1983) divided fish into the following three groups, viz.
(1)Monophagic: This type of fish eats one kind of food.
(2) Stenophagic: This type of fish eats certain selected foods.
(3) Euryphagic: This type of fish eats a variety of foods.
3. Based on the trophic niche in water, fish are divided into the following three groups, viz
(1) Surface feeders: They are plankton-eating in nature. E.g. Catla catla, Rhinomugil corsula, Hypoithalamchthys molitris.
(2) Column feeders: They are carnivorous or omnivorous. Such as- Rohu fish- Labeo rohita
(3) Bottom feeders: They eat bottom food such as rotten food. E.g. Labeo calbasu, Cyprinus carpio, Cirrhina cirrhosus.
4. Fish can be divided into the following categories based on the type of prey and swallowing, e.g.
(1) Predators
Fish that eat large animals as food are called predatory fish. They have acquired some general adaptations to take food. They have well-developed grasping and holding teeth, such as many sharks (Elasmobranchii), Barracuda (Sphyraena), Pike (Esox), and Gers (Lepisosteus). Their intestines tend to be smaller in size than herbivores.
Many predatory fish such as bluegill (Pomatomus saltarix) and many deep sea fish actively hunt their prey. Other fish, such as the grouper (Epinephelus), often sit in wait till an animal passess and then durt out to grasp it. Angler fishes (Lophidae and Antennariidae) have developd an anterior ray of the first dorsal fin into a lure to attract their prey.
The Southeast Asian archer fish (Toxotes jaculata) preys on insects by spitting on nearby trees. This fish has a well-developed aerial viewing system. Some predatory fishes hunt by sight. Other fish, especially many sharks (Squaliformes), nocturnal fish such as bullheads (Ictalurus) and Morays (Muraenidae), catch the prey by ensuring the position of the prey with the help of smell, taste, touch and lateral line organs.
2. Grazers or Browsers
In most cases, small fish eat food by biting. However, sometimes the fish graze alone or in small groups. This type of fish take many plankton or bottom animals as food. Bluegills (Lepomus macrochirus) often eat the larvae of dipteran insects from the bottom of lakes. Many small fish eat plankton-eating fish. Parrot fish (Scaridae) or butterfly fish (Chaetodontidae) graze on coral reefs. They take pieces of polyps or algae from the coral wall as food. Other fish suck on algae or rocks of the same shape if they accidentally fall into their mouths.
3. Parasites
It is perhaps the most unusual and highly evolved feeding habit among animals. In this case, one fish gets shelter and food from the other fish. Some parasitic fish, such as lamprey (Petromyzonidae) and hagfish (Myxinidae), make holes in the sides of the host’s body to absorb body fluids by sucking. Sea lamprey (Petromyzon marinus) of the western North Atlantic and adjacent continents live on the body of the whales as parasite and feed on host’s body fluids by sucking.
Deep sea eel (Simenchelys parasitieus) is also parasitic. Some deep-sea male angler (Ceratias) fish are mandatory parasites of female fish of the same species. In this case, after some time of development, the male finds a female and attaches by his mouth to her body.
Female fish obligatory responds by develoing a fleshy papillae through which males can absorb nutrients. In this case, the males are relatively small. The embryonic nutrient absorption process is seen in the embryos of some baby fish.
4. Strainers
In this case, the fish swallows the living creatures that live in the water. In this case, the food is selected as size. The gills of such fish are very large and are densely packed and form a sieve. Large flocks of many herring-like fish such as Gizard Sads (Dorosoma) and Menhadon (Brevortia tysanus) swim across the Atlantic coast of the United States toward fertile plankton beds.
An adult Menhaden is capable of staining as much as 1-2 gallons of water per minute by gill rakers. This fish can hold a few cubic centimeters of plankton, especially diatoms and crustaceans, in this short time. Other large fish such as paddle fish (Polyodon), basking shark (Cetorhinchus), whale shark (Rhinocodon typus) have efficient adaptations in food selection or filtering.
Figure: Relationship of feeding habits with Gill raker; In Figure (a) to (c) the filtering efficiency is gradually increased: (a) Round white fish (Prosopium cylindraceum) (b) Lake white fish( Coregonus clupeaformis) (c) Black fin sisco (Coregonus nigripinnis) [Source: Hubbs and Lagler 1959]
5. Suckers
In this case, the fish sucks food or food-carrying material inside the mouth. Bottom-feeding fish such as sturgeon (Acipenseridae) and suckers (Catostomidae) have similar feeding processes. Old World Minnows such as Fringelips, Labeo and Osteochilus have inferior face and sucking lips. Moreover, some carp (Cyprinidae) species of Southeast Asia have similar structures.
Figure: Differences in the development of sucking lips and mouth of three Red Horse Suckers (Myxostoma): (a) Short head red horse(Myxostoma macrolepidotum) (b) Golden Red horse (M. erythrurum) (c) Silver red horse(M. anisurum) [Source: Hubbs and Lagler 1958]
In parrot fish, the incisor-like teeth come together to form the incisor lip at the edge. This lip bites a piece of algae and brings it to the mouth separately. A series of pharyngeal teeth in the mouth break them down, exposing the cells and extracting the cell components with the help of digestive juices. Chewing teeth is also able to break down the coral into pieces.
Animals of different types and sizes are needed for the food chain. Basic animal food ingredients are animal plankton or zooplankton. Eggs and larvae of many species, protozoa, microcrustacea and other microscopic invertebrates, fish eggs and larvae include it. Large invertebrates such as Annelida, snails, oysters (Mollusca), crustaceans and insects (Arthropoda), all species of vertebrates such as birds, mammals, reptiles, amphibians, fish are all preyed upon as fish food. Even small rats, snakes and tortoises can be found in the stomachs of pike (Esox), Lepisosteous or Amia.
Figure: Fish teeth and positional differences (a) Upper jaw of Flathead Catfish (Pyloditis olivaris) (b) Deep sea viper fish (Chauliodus sloani) (c) Jaw and pharyngeal teeth in the sagittal section of Parrot fish (Scaridae) (d) Lower jaw of Porgy (Sparidae) (e) Curved teeth in the mouth of Eagle ray(Myliobatis)
Sometimes ducklings and small birds are also seen in the belly of goosefish (Lophius). Moreover, frogs are also found in the stomachs of freshwater predatory fish. So frogs are used to make bait to catch game fish. Even some fish such as Barracuda (Sphyraena), some sharks, Piranha (Serrasalmus) fish attack humans. Bermuda angelfish (Holacanthus bermudensis) change their eating habits as the seasons change. They become completely vegetarian in winter and spring and become carnivorous in early summer and monsoon.
Table: Food and Feeding Habits of Some Popular Teleost Fishes
|
Fish Species |
Food Types |
Feeding Habit |
|---|---|---|
|
Tiny algae, microscopic plants, aquatic insects, rotifers and crustaceans |
Surface feeder (omnivorous) | |
|
Small aquatic plants, leaves of aquatic plants, decaying organic matters, mud |
Column feeder (herbivores) | |
|
Labeo calbasu |
Small plants, insect larvae, decaying organic matters |
Bottom feeder (omnivorous) |
|
Labeo gonius |
Tiny algae, plants, organic matter and mud |
Column and bottom feeder, (herbivorous) |
|
Labeo bata |
Tiny algae, plants, organic matter and mud |
Bottom feeder(herbivorous) |
|
Tiny algae, plants, organic matter and mud |
Bottom feeder(omnivorous) | |
|
Cyprinus carpio |
Algae, microscopic plants, protozoans, insects, rotifers, copepods, crustaceans and chironomus larvae etc. |
Bottom feeder) (omnivorous) |
|
Tor tor |
Aquatic plants, algae, fish, beetles, cricket, shrimps, crabs, snails, and other insects, mollusc, sand or mud etc. |
Bottom feeder, (omnivorous) |
|
Anabas testudineus |
Aquatic herbaceous plants, insects, flies, small fish, decaying organic matters etc. |
Omnivorous |
|
Wallago attu |
Insects, fish larvae, fry, small fish, fingerlings, frogs, tadpoles and other organisms |
Carnivorous, predators |
|
Mystus seenghala |
Insects, fish larvae, fry, fingerlings,small fish, and other organisms |
Carnivorous, predators |
|
Channa striatus |
Insects, fish larvae, fry, fingerlings, small fish, frogs and other organisms |
Carnivorous, predators |
|
Channa marulias |
Insects, fish larvae, fry, fingerlings, small fish, frogs and other organisms |
Carnivorous, predators |
|
Chitala chitala |
Insects, fish larvae, fry, small fish, and other organisms |
Carnivorous, predators |
|
Clarias batrachus |
Worms (nematodes), insects, fish larvae, crustaceans and insect larvae, decaying organic matters, etc. |
Bottom feeder, (carnivorous) |
|
Heteropneustes fossilis |
Algae, nematodes, insects, organic matters and ostracodes etc. |
Bottom feeder, (carnivorous) |