Fish Hatchery Management - fisheries & aquaculture

232 FISH HATCHERY MANAGEMEN'Ibreakdown of fiber has been noted. Herbivorous fish can tolerate higheramounts of fiber than carnivores. It is recommended that crude fiber notexceed l0% in fish feeds and preferably not more than 5 or 6'/n. Some fiberis useful, however, because it supplies bulk and facilitates the passage offood through the fish.PIGMENT-PRODUCING FACTORSoften, producers wish to add color to fish in order to make their productmore attractive to the consumer. This can be achieved through food additives.Paprika fed at 2tlo of the feed will improve the coloration of brooktrout. Xanthophylls from corn gluten meal, dried egg products, and alfalfameal will increase yellow pigmentation of brown trout skin. Shrimp orprawn wastes, which contain carotinoids, produce a reddish colorationwhen fed to trout. Where regulations allow, canthaxanthin can be incorporatedinto trout feeds to impart a red color to the flesh and eggs. Speciesdifferences have been observed, and it is possible to develop color in onespecies of fish, but not another.AN'IIOXIDANTSFish feeds contain high levels of unsaturated oils which are easily oxidized,resulting in breakdown of oils and other nutrients. This can be controlledby the addition of antioxidants such as butylhydroxytoluene (gHf). Uutylhydroxyanisole(BHA), ethoxyquin, and vitamin E. The levels of BHT,BHA, and ethoxyquin allowed in feeds by regulations often are not adequateto control oxidation of the high levels of unsaturated oils in fishfeeds. Therefore, feed formulators should add antioxidants to the levelspermitted by the regulations to protect the oils in fish feeds and supplementwith vitamin E if additional antioxidation is needed. Ethoxyquin andvitamin E are biological antioxidants that function in the fish's physiologicalsystem as well as in feed preservation. The level of vitamin E in fishfeeds must be adequate to prevent oxidation of oils and still meet the nutritionalrequirement of the fish.Materials Afficting Fish QtaliQ and FlaaorFish fed wet feeds containing meat or fish products tend to deposit higherlevels of body fat and have soft textured flesh, whereas those fed dry feedshave a more desirable flavor and firmer flesh. Fresh fish in feeds can impartan off-flavor to the flesh of the fish eating it.