Fish Hatchery Management - fisheries & aquaculture

NUTRITION AND FEEDINGthat the fish would consume, and then giving a little more to assure anabundant supply. Even though given more feed than necessary, the fishoften were underfed because much of the feed was lost as it dispersed inthe water.Nutrition is not solely a matter of feed composition. While it is true thatfish cannot grow if essential elements are lacking in the feed, it is equallytrue that a feed cannot efficiently produce fish unless it can be consumed.The conversion of food into fish flesh is the measure that commonly is usedto judge the efficiency of a feeding program in a hatchery. If the conversionfactor is to be regarded as a measure of efficiency, what can be doneto insure good food conversions?The most common errors in hatcheries are either to overfeed or to underfeed.Overfeeding is wasteful in terms of unconsumed food, butunderfeeding is just as wasteful in terms of lost production. To obtain maximumproduction and feed efficiency during a growing season, careful attentionmust be given, on a daily basis, to the amount of food the fish arereceiving.The quantity of food required is expressed conveniently in terms of percentbody weight per day. Because the metabolic rate per unit weight offish decreases as the fish grow larger, the percent of body weight to be fedper day also decreases.Feeding Guides for SalmonidsThere are several methods for estimating feeding rates. Although differingin complexity, all produce efficient results if properly used.Table 25 may be used to estimate the amount of dry pelleted feed neededfor rainbow trout. For a given fish size, the amount of food increaseswith increasing water temperature; for a given water temperature theamount of feed decreases with increasing fish size.Table 26 was developed by Oregon Fish and Wildlife Department for estimatingthe amount of moist feed to give to coldwater species. A higherpercent of body weight must be fed than in the case of dry pellets becauseof the greater water content in moist feed.Feeding tables provide a guide for determining the amount of feed togive salmonids. In general, these yield good results. However, there are situationsin which the amounts should be increased or reduced. When thewater begins to warm in the spring, the fish indicate an accelerated metabolismby their increased activity and by the vigor with which they feed.At this time of the year, when the photoperiod also is increasing, it is possibleto feed in excess of (up to twice) the amounts in the tables and obtain