Fish Hatchery Management - fisheries & aquaculture

234 FISH HATCHERY MANAGEMFNTFORMULATED FEEDSFormulated feeds are a mixtureof ingredients processed into pellets,granules, or meals and may be either supplemental or complete rations.Supplemental feeds are formulated to contain adequate protein and energy,but may be deficient in vitamins and minerals which the fish are expectedto obtain from natural foods. Such feeds are fed to catfish and otherfish reared at low densities in ponds.Complete feeds are formulated to provide all essential vitamins and nutrientsrequired by fish and are designed to provide optimal growth. If highdensities of fish are being reared, a complete feed must be provided, as naturalfeeds will be limited or absent. Such feeds must be of a physical consistencythat will allow them to be fed in the water without breaking down,but still be easily ingested and digested by the fish. Properly sized feedsare required for different sizes of fish because fish normally do not chewtheir food. The feed must be palatable to the fish so that it will be readilyconsumed and not left to dissipate into the water. Dust and fine particlesthat may occur in the large-sized feeds will create problems because theyare not efficiently consumed and, if present in excess, cause water pollutionand gill disease.Feed ManufacturingFormulated feeds are manufactured in the forms of meals, granules,compressed pellets (sinking), expanded pellets (floating), and semimoistpellets. The use of dry pelleted feeds provides several advantages over otherfeeding programs. Such feeds are available at all times of the year in anyquantity. Fish producers can select the size of feed satisfactory for feedingfish through the rearing cycle. Pelleted feeds give lower feed conversionsand lower feed cost per unit of weight gain than natural or wet feeds andcause less waste and contamination of the rearing water. No hatchery laboris required to prepare the feed. Pelleted feeds purchased in bulk provideadditional efficiency in lower costs of handling and storage. The convenienceof using automatic feeding equipment is also possible with bulkfeeds.Compressed or sinking pellets are made by adding steam to the feed as itgoes into the pellet mill. The steam increases the moisture content by 5 to6%, and raises the temperature to 150-180"F during processing. The mixtureis forced through a die to extrude a compressed, dense pellet. The pelletsare air-dried and cooled immediately after pelleting. The moisture contentof pellets must be sufficiently low (less than l0o,') to prevent moldgrowth during storage.