Fish Hatchery Management - fisheries & aquaculture

238 FISH HATCHERY MANAGEMENTphysical conditions (moisture, heat, light) ; oxidation; micro-organisms(molds, bacteria, yeast) ; and enzymatic action.Feed in bags or bulk should be stored in a cool, dry area. Low humiditymust be maintained because moisture enhances mold growth and attractsinsects. Molds, which grow when the moisture is l37o or above, cause feedspoilage and may produce toxins. High temperatures may cause rancidityof oils and deterioration of vitamins. Rancid oils can be toxic, may destroyother nutrients, will cause off-flavor of the feed, and will produce an undesirableflavor in fish eating the feed. The storage area should be keptclean and adequately ventilated. The stored feed should be protected fromrodents, insects, and contamination.Ideal conditions for storing bagged dry feed include stacking the bagsnot over ten high on pallets so the bags are 3 to 4 inches off the floor.Space should be provided between the stacks for air circulation and rodentcontrol. Low relative humidityreduce the rate of deterioration in feeds.The recommended maximumand low temperature in the storage areastorage time for dry pelleted feeds is90-100 days. If less than optimal storage conditions exist, the storage timeshould be shortened.Bulk feed should be stored in clean bins free of contaminants or spoiledfeed. The bins must be in good condition to protect the feed from waterand weather elements. Bins located in shaded areas remain cooler. Bins canbe fitted with a screening unit on the discharge to remove dust and finesfrom the pellets. In many cases the fines can be returned to the feed millfor repelleting or be used to fertilize ponds.Moist pellets should be stored in the freezer at temperatures below 0'Funtil they are to be fed, then thawed just prior to feeding.Feed EaaluationThe performance of feeds often is measured to evaluate or compare them.The measurements used to evaluate feeds at production hatcheries are: (1.)fish growth (weight and length) ; (2) feed conversion; (3) cost to rear apound of fish; (4) protein and calories required to rear a pound of fish; and(5) mortality and dietary deficiency symptoms.FeedingFeeding once was considered a simple task and was usually assigned to theleast experienced fish culturist. The chore consisted of merely feeding all