NUTRITION AND FEEDING 



227 



The available calories in catfish feeds and estimated feed conversions can 

 be calculated by the same procedures as for salmonid feeds, with appropri- 

 ate values for catfish being substituted. 



Vitamin Requirements 



Vitamins are not nutrients, but are dietary essentials required in small 

 quantities by all forms of plant and animal life. They are catalytic in na- 

 ture and function as part of an enzyme system. 



For convenience, vitamins are broadly classified as fat-soluble vitamins 

 or water-soluble vitamins. The fat-soluble vitamins usually are found asso- 

 ciated with the lipids of natural foods and include vitamins A, D, E, and 

 K. The water soluble vitamins include vitamin C and those of the B com- 

 plex: thiamine (B,), riboflavin (B^), biotin, folic acid, cyanocobalamin (B12) 

 and inositol. 



Vitamins are distributed widely in ingredients used in fish feeds. Some, 

 such as yeast, contain high levels of several vitamins. The level of vitamins 

 supplied by the ingredients in the feed usually is not adequate to meet the 

 fishes' requirements. These requirements are presented in Table 24. Most 



Table 24. vitamin requirements expressed as milligrams or interna- 

 tional UNITS (lU) PER POUND OF DRY FEED FOR SALMONIDS AND WARMWATER 

 FISHES. (SOURCE: NATIONAL RESEARCH COUNCIL 1973, 1977.) 



Required level is not established. 



Brown trout require twice the level presented. 



