Fish Hatchery Management - fisheries & aquaculture

FISH HA'I'CHERY MANAGE,MENTNo carbohydrate requirements have been established for catfish; however,carbohydrates can spare protein in catfish feeds. In the absence ofadequate dietary carbohydrates or fats, catfish make inefficient use ofdietary protein to meet their energy and other metabolic needs. In channelcatfish, lipids and carbohydrates appear to spare protein in lower-energyfeeds but not in higher-energy feeds.Fiber is an indigestible dietary material derived from plant cell walls.Fiber is not a necessary component for optimum rate of growth or nutrientdigestibility in channel catfish production rations. Fiber levels as high as2l% reduce nutrient intake and impair digestibility in feeds for channelcatfish. Fiber in concentrations of less than [J')t may add structural integrityto pelleted feeds, but larger amounts often impair pellet quality. Most ofthe fiber in the feed ultimately becomes a pollutant in the water.Lipid RequirementsLipids comprise a group of organic substances of a fatty nature that includesfats, oils, waxes, and related compounds. Lipids are the most concentratedenergy source of the food groups, having at least 2.25 times moreenergy per unit weight than either protein or carbohydrates. In addition tosupplying energy, lipids serve several other functions such as reserve energystorage, insulation for the body, cushion for vital organs, lubrication,transport of fat-soluble vitamins, and maintenance of neutral bouyancy.They provide essential lipids and hormones for certain body processes andmetabolism, and are a major part of reproductive products.Although each fish tends to deposit a fat peculiar to its species, the dietof the fish will alter its type. The fat deposited tends to be similar to thefat ingested. The body fat of fish consuming natural foods contains a highdegree of polyunsaturated (soft) fats similar to those in the food. Becausenatural fats are soft fats that are mobilized and utilized by the fish more efficientlythan hard (saturated) fats, soft fats are beneficial for efficient productionand fish health. Preliminary studies have indicated that some hardfats can be used by warmwater fish.The effect of water temperature on the composition of the body fat offish is difficult to define clearly due to its influence on the digestibility ofhard and soft fats. Soft fats are digested easily in both warm and cold water,but hard fats are digested efficiently only in warm water. Fish living incold water have body fats that are highly unsaturated with a low meltingpoint. These fish are able to more readily adapt to a low environmentaltemperature.Factors to be considered in evaluating dietary lipids for fish feeds includedigestibility, optimal level in the feed, content of fatty acids essential