228 FISH HATCHERY MANAGEMENT 



vitamins can be manufactured synthetically; these are both chemically and 

 biologically the same as naturally occurring substances. Synthetic vitamins 

 can be added to feeds with great precision as a mixture (referred to as a 

 premix) to complement the natural vitamins and balance the vitamin con- 

 tent of the finished feed. 



Calculations of the vitamin levels to be placed in feeds should provide 

 for an excess, for several reasons: (l) the efficiency with which fish use the 

 vitamins in ingredients is unknown; (2) vitamins in fish feeds are destroyed 

 by heat and moisture primarily during manufacturing but also during 

 storage; (3) breakdown of other substances in the feed (such as oxidation 

 of oils) may destroy some vitamins; and (4) vitamins react with other com- 

 pounds and become inactive. 



Several vitamins show moderate to severe losses when incorporated into 

 feeds and stored at different temperatures and relative humidities. Among 

 them are vitamins A, D, K, C, E, thiamine, and folic acid. Vitamin C (as- 

 corbic acid) has received considerable attention. Typical losses of vitamin 

 C in feeds are: 



Storage 



Feed Temperature Duration Loss 



Catfish feeds (dry) 70°F 3 months 50% 



Oregon moist pellet — 14°F 3 months None 



40-46°F 3 days 85% 



70°F 11 hours 81% 



Assays performed on Oregon moist pellet that had been stored 5 months 

 and then thawed for 14 hours showed reductions of vitamin levels as fol- 



lows: 



Change in 

 Vitamin concentration (mg/kg diet) 



C 893 to 10 



E 503 to 432 



K 18.6 to 2.0 



Folic acid 7.1 to 5.3 



Pantothenic acid 106 to 99 



Vitamin E is reduced continually from the time the feed is manufactured 

 until it is fed, due to oxidative rancidity of oils in the feed; vitamin E 

 serves as an antioxidant. For these reasons, all feeds should be used within 



