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. In this case, live fish food play an important role in aquaculture.
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:
- Natural food and
- 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:
- Phytoplankton
- 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
Plankton play an crucial role in aquaculure. 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:
- Arginine,
- Histidine,
- Isoleucine,
- Lucine,
- Lysine,
- Methionine,
- Tryptophan,
- Phenylalanine,
- Threonine and
- 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.