NUTRITION AND FEEDING 239 



that the fish would consume, and then giving a little more to assure an 

 abundant supply. Even though given more feed than necessary, the fish 

 often were underfed because much of the feed was lost as it dispersed in 

 the water. 



Nutrition is not solely a matter of feed composition. While it is true that 

 fish cannot grow if essential elements are lacking in the feed, it is equally 

 true 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 used 

 to judge the efficiency of a feeding program in a hatchery. If the conver- 

 sion factor is to be regarded as a measure of efficiency, what can be done 

 to insure good food conversions? 



The most common errors in hatcheries are either to overfeed or to un- 

 derfeed. Overfeeding is wasteful in terms of unconsumed food, but 

 underfeeding is just as wasteful in terms of lost production. To obtain max- 

 imum production and feed efficiency during a growing season, careful at- 

 tention must be given, on a daily basis, to the amount of food the fish are 

 receiving. 



The quantity of food required is expressed conveniently in terms of per- 

 cent body weight per day. Because the metabolic rate per unit weight of 

 fish decreases as the fish grow larger, the percent of body weight to be fed 

 per day also decreases. 



Feeding Guides for Salmonids 



There are several methods for estimating feeding rates. Although differing 

 in complexity, all produce efficient results if properly used. 



Table 25 may be used to estimate the amount of dry pelleted feed need- 

 ed for rainbow trout. For a given fish size, the amount of food increases 

 with increasing water temperature; for a given water temperature the 

 amount of feed decreases with increasing fish size. 



Table 26 was developed by Oregon Fish and Wildlife Department for es- 

 timating the amount of moist feed to give to coldwater species. A higher 

 percent of body weight must be fed than in the case of dry pellets because 

 of the greater water content in moist feed. 



Feeding tables provide a guide for determining the amount of feed to 

 give salmonids. In general, these yield good results. However, there are si- 

 tuations in which the amounts should be increased or reduced. When the 

 water begins to warm in the spring, the fish indicate an accelerated meta- 

 bolism by 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 pos- 

 sible to feed in excess of (up to twice) the amounts in the tables and obtain 



