Fish Hatchery Management - fisheries & aquaculture

224 FISH HA t CHITRY MANAGEMIlNTLIPID RN,qUIRN,ME,NTS FOR CATFISHLipid level and content of essential fatty acids have received little considerationin diets for channel catfish, because little is known about the effectsof, and requirements for, these nutrients in catfish. In practice, thedietary requirements have been met reasonably well by lipids in the fishmeal and oil-rich plant proteins normally used in catfish feeds and those innatural food organisms available in ponds.Weight gain and protein deposition increase as the level of fish oil iselevated to 15')6 of the dry feed. At the 20([r level, the gain decreases. Catfishfed corn oil did not gain as well as those fed fish oil in the feed, showingthat fish oil is a better source of dietary lipid.Beef tallow, safflower oil, and fish oil were evaluated at temperaturesfrom 68 to 93'F. Maximum growth was obtained at 86"F by catfish fedeach lipid supplement. Highest gains and lowest food conversion rates wereobtained with fish oil, followed by beef tallow and safflower oil. As withsalmonids, catfish have little or no requirement for linoleic (omega-6) fattyacids in the feed. No requirements for essential fatty acids in catfish feedshave been determined.Commercial catfish feeds contain less than 8(!l dietary lipids. Test feedswith 10% lipid provided the best growth, whereas 16')l in the feed did notimprove 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 significantadverse effect on the flavor of fresh and frozen fish. Beef tallow also influencedthe flavor, but did not induce the "fishy" flavor produced by thefish oil. Fish reared on safflower oil or corn oil have a better flavor thanthose fed beef tallow or fish oil. Catfish producers may be able to use animalfats and oils in fingerling feeds to obtain rapid growth and efficientdeposition of protein, then change to a finishing diet made with vegetableoils to improve the flavor as the fish approach market size.Energt RequirementsEnergy 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, activity,reproduction, and osmotic balance. Energy requirements of speciesdiffer, as do their growth rates and activities. Other factors that alter theenergy 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 isreleased in two forms, heat energy and free energy, in animal systems. Heatenergy has the biological purpose of maintaining body temperature in