of a practical diet for the blviebjuk [red | 

 salmon than any other developed to date, 

 niis diet at tenii)eratures above 50° F. 

 consists of 20 i>erceut each of beef livei-, 

 hoR liver, and hog spleen^ SO percent 

 salmon viscera, and 10 percent flame-dried 

 siilmon-offal meal. At temperatures be 

 l(i\v r>()° the meal is deleted from the die! 

 and tlio other ingredients increased pro 

 Ijortionally. 



At all salmon and trout hatcllel■ie^^ 

 the objective is to produce healthy 

 fish at the minimum cost. One gen- 

 eral measure of success is the pounds 

 of food required to produce a pound 

 of salmon or trout. A few years 

 ago 4: to 5 or more pounds of food 

 were required to produce a pound of 

 Hsh. This ratio has been consider- 

 ably reduced through research ; now 

 it is not uncommon to average about 

 3 pounds of food to 1 pound of fish. 

 In general, costs, too, have been 

 reduced, but this does not neces- 

 sarily follow, as the foods in the 

 low-ratio diet may be more expen- 

 sive than those in other diets. 



At salmon hatcheries of the Fish 

 and Wildlife Service, it is con- 

 sidered most desirable for the fish 

 to be presented suitably prepared 

 food that floats on the surface of the 

 water for a time. This is accom- 

 plished by preparing food that does 

 not easily separate in the water. 

 There is less leaching of the food, 

 and consequently almost all of the 

 food is available to the fish. Cer- 

 tain ingredients tend to bind foods 

 together. Salt in combination with 

 hog, beef, or horse liver will form 

 a rubberlike mass that is resistant 

 to water. Dry^ meals in a food will 

 absorb the nutritive juices of the 

 meats, and the binding action will 



hold tlie food together so fish will 

 receive the full benelit. 



Reconnnended hatchery practice 

 is to juvpare and feed a food in 

 the same (h>y or within -21 lioui's at 

 the uiost. l*repared foods should 

 not be ref rozen but shoidd be held at 

 low temperatures. 



The preparation of food involves 

 grinding the components to a fine- 

 ness required for the fish size, mix- 

 ing, and presenting the prepared 

 food to the fish at regular inter- 

 vals — several times each day to 

 newly feeding fish and once or twice 

 daily to larger fish. For the small 

 fish the consistency of a diet may be 

 changed so that the food will break 

 up more readily in the water to pro- 

 vide particles fine enough for the 

 fish. 



The quantity of food to be pre- 

 sented to the fish is governed by size, 

 species, and the temperatures of the 

 water. The water temperature de- 

 termines the activity of the fish and 

 of the digestive processes. The in- 

 take of food to meet nutritive re- 

 quirements increases as the water 

 temperature rises, and vice versa. 

 Growth of salmon in hatcheries is 

 extremely rapid during the first 

 year of life, when the body weight 

 increases many fold. The food re- 

 quirements of the various species of 

 salmon and trout are definitely dif- 

 ferent. As a general guide to the 

 feeding of salmonoids, charts have 

 been prepared by which the quan- 

 tities of food to be fed to a pond of 

 fish may be determined if the total 

 weight of the fish in the pond is 

 known. The first charts w^ere by 

 Tunison (1936) and by Deuel, 

 Haskell, and Tunison (1937, 1942). 



35 



