224 FISH HAICHKRY MANAGEMENT 



LIPID REQUIREMENTS FOR CA lEISH 



Lipid level and content of essential fatty acids have received little con- 

 sideration in diets for channel catfish, because little is known about the ef- 

 fects of, and requirements for, these nutrients in catfish. In practice, the 

 dietary requirements have been met reasonably well by lipids in the fish 

 meal and oil-rich plant proteins normally used in catfish feeds and those in 

 natural food organisms available in ponds. 



Weight gain and protein deposition increase as the level of fish oil is 

 elevated to 15'^ of the dry feed. At the 20'}(i level, the gain decreases. Cat- 

 fish fed corn oil did not gain as well as those fed fish oil in the feed, show- 

 ing that fish oil is a better source of dietary lipid. 



Beef tallow, safflower oil, and fish oil were evaluated at temperatures 

 from 68 to 93°F. Maximum growth was obtained at 86°F by catfish fed 

 each lipid supplement. Highest gains and lowest food conversion rates were 

 obtained with fish oil, followed by beef tallow and safflower oil. As with 

 salmonids, catfish have little or no requirement for linoleic (omega-6) fatty 

 acids in the feed. No requirements for essential fatty acids in catfish feeds 

 have been determined. 



Commercial catfish feeds contain less than 8% dietary lipids. Test feeds 

 with 10% lipid provided the best growth, whereas 167(1 in the feed did not 

 improve growth or enhance protein deposition. 



Lipids have the most effect on taste and storage quality of fish products. 

 Tests with animal and vegetable fats showed that fish oil has a significant 

 adverse effect on the flavor of fresh and frozen fish. Beef tallow also influ- 

 enced the flavor, but did not induce the "fishy" flavor produced by the 

 fish oil. Fish reared on safflower oil or corn oil have a better flavor than 

 those fed beef tallow or fish oil. Catfish producers may be able to use an- 

 imal fats and oils in fingerling feeds to obtain rapid growth and efficient 

 deposition of protein, then change to a finishing diet made with vegetable 

 oils to improve the flavor as the fish approach market size. 



Energy Requirements 



Energy is defined as the capacity to do work. The work can be mechanical 

 (muscular activity), chemical (tissue repair and formation), or osmotic 

 (maintenance of biological salt balance). Fish require energy for growth, ac- 

 tivity, reproduction, and osmotic balance. Energy requirements of species 

 differ, as do their growth rates and activities. Other factors that alter the 

 energy requirements are water temperature, size, age, physiological activity, 

 composition of the diet, light exposure, and environmental stresses. 



Food energy is usually expressed as kilogram calories (kcal or Cal). It is 

 released in two forms, heat energy and free energy, in animal systems. Heat 

 energy has the biological purpose of maintaining body temperature in 



