With few exceptions, feeding a single type of food is neither complete nor balanced and does not supply all the nutrients a fish might need in its diet. Hence, two or more ingredients should be mixed into homemade, laboratory and commercial feed formulations. Fish need energy and essential nutrients for maintenance, movement, normal metabolic functions and growth. Fish can obtain their energy and nutrients from natural food in ponds, from feed supplied by the farmer or form a combination of both sources.
The feed requirements of fish vary in quantity and quality according to their feeding habits and digestive anatomy as well as their size and reproductive state. Feed requirements are also affected by environmental variations such as temperature and the amount and type of natural food available.
Nutrients essential to fish are the same as those required by most other animals. These include moisture (water), proteins (amino acids), lipids (fats, oils, fatty acids), carbohydrates (sugars, starch), vitamins and minerals. Fish obtain the energy they need by eating protein, lipid and carbohydrate.
General amounts of nutrients incorporated into diets for growing fish:
| Nutrients | Requirement (percent by dry diet) |
|---|---|
| Proteins (10 essential amino acids):
Lysine, phenylalanine, arginine, valine, leucine, isoleucine, methionine, threonine, tryptophan and histidine |
32-45% |
| Fat: used as a source of energy
and polyunsaturated fatty acids. In general, freshwater fish require fatty acids of the linolenic (w-3) and linoleic (w-6) series. Saltwater and coldwater fish require EPA and DHA(w-3). |
4-28% (should contain
at least 1-2% of the w-6 or w-3 essential fatty acid series) |
| Carbohydrates: these are an inexpensive source
of energy and is a binding agent. No essential requirements have been identified. These are poorly digested when fed raw highest digestibility is achieved when cooked. Major carbohydrates are starch, cellulose and pectin. |
10-30% |
| Minerals: some 20 inorganic mineral elements,
including calcium, phosphorous, magnesium, iron, copper, manganese, zinc, iodine and selenium. |
1.0-2.5% fed as a multi-mineral premix |
| Vitamins: these are inorganic substances required in
trace amounts that can be divided into fat-soluble (vitamins A, D, E and K) and water-soluble (vitamins C and the B-complex [thiamin, riboflavin, pyridoxine, pantothenic acid, cyanocobalamin, miacin, biotin, folic acid, choline and myoinositol) |
1.0-2.5% fed primarily
as a multi-vitamin premix. Vitamin C and choline are added separately from the premix because of their chemical instability. |
Another important ingredient in fish diets is a binding agent to provide stability to the pellet and reduce leaching of nutrients into the water. Beef heart has traditionally been used both as a source of protein and as an effective binder in farm-made feeds. Carbohydrates (starch, cellulose, pectin) and various other polysaccharides, such as extracts or derivatives from animals (gelatin), plants (gum arabic, locust bean), and seaweeds (agar, carageenin, and other alginates) are also popular binding agents.
Other common feedstuffs used in ornamental fish diets include live, frozen, or dried algae, brine shrimp, rotifers or other zooplankton. The addition of fish or squid meal will enhance the nutritional value of the diet and increase its acceptance by the fish. Fresh leafy or cooked green vegetables are often used. Although vegetables are composed mainly of water, they contain some ash, carbohydrates, and certain vitamins. Kale, dandelion greens, parsley, and turnip greens are examples of relatively nutritious vegetables.