Full-fat Soybeans
The use of full-fat soybean meal in fish feeds has received attention since research by the U.S. Fish and Wildlife Service showed that heating full-fat soybeans at high temperature (≥ 177°C) improved the nutritional value for trout above that of commercial soybean meal. Canadian research, however, found that feeding a diet containing high levels (≥80%) of full-fat soybean meal reduced weight gain for rainbow trout, presumably because it reduced consumption by the fish because of its higher energy and/or lower palatability. Trout fed full-fat soybean diets were significantly fatter. Channel catfish fed protein but much more fat than fish fed diets containing solvent extracted soybean meal. Full-fat soybean meal contains 18% fat compared with 0.5% fat for solvent-extracted soybean meal. The improves the nutritional quality of the diet. Too much fat can cause an imbalance of protein and energy in the ration, which can reduce nutrient intake and also produce fatty fish. The additional fat in full-fat soybean meal would be more beneficial to coldwater fish, who do not utilize carbohydrates well for energy.
Cottonseed Meal
Cottonseed meal is an important source of protein in the United States and is available in many other parts of the world for animal feeds. Initially, formulated fish feeds in the United States contained significant amounts of cottonseed meal; however, after fish meal and other animal proteins decreased in content in commercial fish feeds, cottonssed meal was eliminated form many fish feed formulas because of its low available lysine content. Supplementing cottonseed meal with crystalline amino acids could possibly make it more competitive for use in fish feeds, Because research has shown that the protein quality of peanut meal can be improved for channel catfish by supplementation with synthetic lysine.
Another liability of cottonseed meal is its content of free gossypol, which is moderately toxic to monogastric animals. Approximately 0.03% free gossypol will suppress growth rate in rainbow trout (Herman 1970). Levels of ≥ 20% prepress solvent-extrated cottonseed meal in channel catfish diets cause gossypol toxicity, but lower levels processing (Lovell 1981). Generally, free gossypol contents of three types of cottonseed meal are as follows: direct solvent meal, 0.2% to 0.4% ; screwpress meal, 0.02%; prepress solvent, 0.05%. The addition of 0.85 to 1.0 part ferrous sulfate to each part free gossypol in diets of swine and poultry has proven successful in blocking the toxic effects of gossypol.
Other Oilseed Meals
Meals from peanut (groundnut) and sunflower seed have been used in fish feeds in the United States. Compared with soybean meal, these are deficient in lysine and methionine. Peanut meal produced in the United States contains around 48% crude protein, is highly palatable, and contains no toxins or anti-nutritional factors. It also has better binding properties for pelleting than soybean meal. Sunflower meal is also palatable, but relatively fibrous. Canola meal, produced mainly in Canada, is comparable in protein quality to soybean meal but contains glucosinase enzymes, which hydrolyze glucosinolate to yield antithyroid products, thus making it a poor protein source for fish.