Fish Hatchery Management - fisheries & aquaculture

228 F'ISH HATCHERY MANAGL,MEN'Ivitamins can be manufactured synthetically; these are both chemically andbiologically the same as naturally occurring substances. Synthetic vitaminscan be added to feeds with great precision as a mixture (referred to as apremix) to complement the natural vitamins and balance the vitamin contentof the finished feed.Calculations of the vitamin levels to be placed in feeds should providefor an excess, for several reasons: (1) the efficiency with which fish use thevitamins in ingredients is unknown; (2) vitamins in fish feeds are destroyedby heat and moisture primarilyduring manufacturing but also duringstorage; (3) breakdown of other substances in the feed (such as oxidationof oils) may destroy some vitamins; and (4) vitamins react with other compoundsand become inactive.Several vitamins show moderate to severe losses when incorporated intofeeds and stored at different temperatures and relative humidities. Amongthem are vitamins A, D, K, C, E, thiamine, and folic acid. Vitamin C (ascorbicacid) has received considerable attention. Typical losses of vitaminC in feeds are:StorageTemperature Duration LossCatfish feeds (dry)Oregon moist pellet70"F-14"F40 46'F70'F3 months 50'/o3 months None3 days 85%I I hours 8l'/oAssays performed on Oregonand then thawed for 14 hourslows:moist pellet that had been stored 5 monthsshowed reductions of vitamin levels as fol-VitaminCEKFolic acidPantothenic acidChange inconft nlralion hg/kg dict)tt93 to 10503 to 43218.6 to 2.07.1 to 5.3106 to 99Vitamin E is reduced continually from the time the feed is manufactureduntil it is fed, due to oxidative rancidity of oils in the feed; vitamin Eserves as an antioxidant. For these reasons. all feeds should be used within