Fish Hatchery Management - fisheries & aquaculture

NU'IRITION AND I'E,EDING 229a 3-month period if at all possible. It is important to store fish feed in acool dry place and to avoid prolonged storage if fish are to be providedwith levels of vitamins originally formulated into the feed. Steps can betaken to help preserve the vitamins in the feed. Some synthetic vitaminscan be protected by a coating of gelatin, fat, or starch. The addition of antioxidantsreduces the oxidation of oils and its destructive effect on vitamins.Maintaining cool, dry storage conditions to eliminate spoilage andmold growth preserves the feed quality and vitamins.Because the metabolic processes and functions of biological systems offish are similar to those of other animals, it is safe to assume that all vitaminsare required by all species. However, the recommended amounts ofthe vitamins for different fishes vary. The required levels of vitamins mustbe added to the ration routinely in order to prevent deficiencies from occurring(Figures 72 and 73). Deficiencies of most known vitamins havebeen described (Appendix F).The total amount of vitamins required by a fish increases as the fishgrows. Conversely, food intake decreases as a percent of body weight as thefish increases in size, which can cause a vitamin deficiency if the feed containsonly the minimum level of vitamins. Therefore, feeds for older fishalso need to be fortified with vitamins.As temperature decreases, so does food intake. However, the vitamin requirementsof fish do not decrease proportionally. A vitamin deficiency canoccur with low intake of diets containing marginal levels of vitamins.Complete catfish feeds are formulated to contain all of the essential vitaminsin amounts required by the fish and are designed to provide normalgrowth for fish that do not have access to natural feeds. Supplemental feedscontain the vitamins supplied by the feed ingredients plus limited supplementation,as the fish are expected to obtain vitamins from natural foodsin the pond.Mineral RequirementsAs nutrients in fish feeds, minerals are difficult to study. Absorption andexcretion of inorganic elements across the gills and skin have an osmoregulatoryas well as a nutritional function. Absorption of inorganic elementsthrough 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 typeof ration being fed. Dietary requirements for most minerals have not beenestablished for fish, but fish probably require the same minerals as other