232 FISH HATCHERY MANAGEMENT 



breakdown of fiber has been noted. Herbivorous fish can tolerate higher 

 amounts of fiber than carnivores. It is recommended that crude fiber not 

 exceed 10% in fish feeds and preferably not more than 5 or 6%. Some fiber 

 is useful, however, because it supplies bulk and facilitates the passage of 

 food through the fish. 



PIGMENT-PRODUCING FACTORS 



Often, producers wish to add color to fish in order to make their product 

 more attractive to the consumer. This can be achieved through food addi- 

 tives. Paprika fed at Tin of the feed will improve the coloration of brook 

 trout. Xanthophylls from corn gluten meal, dried egg products, and alfalfa 

 meal will increase yellow pigmentation of brown trout skin. Shrimp or 

 prawn wastes, which contain carotinoids, produce a reddish coloration 

 when fed to trout. Where regulations allow, canthaxanthin can be incor- 

 porated into trout feeds to impart a red color to the flesh and eggs. Species 

 differences have been observed, and it is possible to develop color in one 

 species of fish, but not another. 



ANTIOXIDANTS 



Fish feeds contain high levels of unsaturated oils which are easily oxidized, 

 resulting in breakdown of oils and other nutrients. This can be controlled 

 by the addition of antioxidants such as butylhydroxytoluene (BHT), bu- 

 tylhydroxyanisole (BHA), ethoxyquin, and vitamin E. The levels of BHT, 

 BHA, and ethoxyquin allowed in feeds by regulations often are not ade- 

 quate to control oxidation of the high levels of unsaturated oils in fish 

 feeds. Therefore, feed formulators should add antioxidants to the levels 

 permitted by the regulations to protect the oils in fish feeds and supple- 

 ment with vitamin E if additional antioxidation is needed. Ethoxyquin and 

 vitamin E are biological antioxidants that function in the fish's physiologi- 

 cal system as well as in feed preservation. The level of vitamin E in fish 

 feeds must be adequate to prevent oxidation of oils and still meet the nu- 

 tritional requirement of the fish. 



Materials Affecting Fish Quality and Flavor 



Fish fed wet feeds containing meat or fish products tend to deposit higher 

 levels of body fat and have soft textured flesh, whereas those fed dry feeds 

 have a more desirable flavor and firmer flesh. Fresh fish in feeds can im- 

 part an off- flavor to the flesh of the fish eating it. 



