NUTRITION AND FEEDING 229 



a 3-month period if at all possible. It is important to store fish feed in a 

 cool dry place and to avoid prolonged storage if fish are to be provided 

 with levels of vitamins originally formulated into the feed. Steps can be 

 taken to help preserve the vitamins in the feed. Some synthetic vitamins 

 can be protected by a coating of gelatin, fat, or starch. The addition of an- 

 tioxidants reduces the oxidation of oils and its destructive effect on vita- 

 mins. Maintaining cool, dry storage conditions to eliminate spoilage and 

 mold growth preserves the feed quality and vitamins. 



Because the metabolic processes and functions of biological systems of 

 fish are similar to those of other animals, it is safe to assume that all vita- 

 mins are required by all species. However, the recommended amounts of 

 the vitamins for different fishes vary. The required levels of vitamins must 

 be added to the ration routinely in order to prevent deficiencies from oc- 

 curring (Figures 72 and 73). Deficiencies of most known vitamins have 

 been described (Appendix F). 



The total amount of vitamins required by a fish increases as the fish 

 grows. Conversely, food intake decreases as a percent of body weight as the 

 fish increases in size, which can cause a vitamin deficiency if the feed con- 

 tains only the minimum level of vitamins. Therefore, feeds for older fish 

 also need to be fortified with vitamins. 



As temperature decreases, so does food intake. However, the vitamin re- 

 quirements of fish do not decrease proportionally. A vitamin deficiency can 

 occur with low intake of diets containing marginal levels of vitamins. 



Complete catfish feeds are formulated to contain all of the essential vita- 

 mins in amounts required by the fish and are designed to provide normal 

 growth for fish that do not have access to natural feeds. Supplemental feeds 

 contain the vitamins supplied by the feed ingredients plus limited supple- 

 mentation, as the fish are expected to obtain vitamins from natural foods 

 in the pond. 



Mineral Requirements 



As nutrients in fish feeds, minerals are difficult to study. Absorption and 

 excretion of inorganic elements across the gills and skin have an osmoregu- 

 latory as well as a nutritional function. Absorption of inorganic elements 

 through the digestive system also affects osmoregulation. 



The specific qualitative and quantitative dietary needs will, therefore, 

 depend upon the environment in which the fish is reared and on the type 

 of ration being fed. Dietary requirements for most minerals have not been 

 established for fish, but fish probably require the same minerals as other 



