BUREAU OF FISHERIES 119 



aquiculture are directly concerned with the reduction of this waste by 

 determining at what age and under what conditions fish should be 

 planted to insure maximum returns. Improvement of hatchery prac- 

 tices in feeding and selective breeding and the reduction of loss 

 through disease are also under investigation. 



Fisii management practices which have been developed by many 

 years' experimentation are being tested in various national forest areas 

 throughout the countr}^ which serve as excellent natural laboratories 

 for this purpose. In the Pisgah National Forest project, operated 

 in cooperation with the Forest Service, studies were carried out during 

 the year to determine what size of fish and wdiat intensity of stocking 

 produce most satisfactory results. The effects of various stream im- 

 provements on the production of fish and food organisms are also the 

 subject of studies which will find widespread application. 



In California, experiments of an essentially similar nature were 

 carried out during the summers of 1937 and 1938 in tlie Convict Creek 

 Experimental Stream. The survival rates of various species, sizes, 

 and numbers of trout were compared as a guide for stocking programs. 

 Among the results obtained was the finding that hatchery fish of 2 

 inches or more show a surprisingly high survival in wild waters, and 

 that there is a distinct species difference in ability to make adjustments 

 to new conditions after planting. 



The continued operation of test waters in Vermont shows conclu- 

 sively that stocking alone is not enough to maintain the supply in the 

 waters under observation, for, while the species stocked (brook trout) 

 has shown a consistent decline, the rainbow trout, which is dependent 

 on natural propagation, has held its own. 



Fundamental studies in the science of fish nutrition have been con- 

 tinued at Cortland, N. Y. Two lines of attack were made on the 

 problems presented. The first was concerned with improving current 

 hatchery practices by introducing new foodstuffs that are readily 

 available, and by improving the quality of the mixtures in current use. 

 In this connection a process has been developed for freeing linseed 

 meal of its toxic properties by steaming and pressure cooking, while 

 retaining its important property of binding water or meat juices. 

 Progress has been made toward keeping meats for long periods without 

 loss of nutritive value or physical properties, a development which 

 would decrease the labor and investment in refrigeration equipment 

 and make it possible to purchase meat in quantity at periods of low 

 prices. 



Field studies in bass streams are concerned with much the same 

 problems as trout studies in colder w^aters. Studies in selected waters 

 of natural spawning, survival of the young, their food habits and 

 growth, lead to the tentative conclusion that, in the case of bass, 

 natural propagation is more efficient than artificial, and suggest that 

 management practices should be directed chiefly to the improvement 

 of natural conditions. 



Experimental studies of fish diseases were continued. The value 

 of routine preventive treatments is being tested, and records are being 

 carefully kept of possible mortality from such treatments. No in- 

 crease in mortality w^as found among fimrerling trout. Controlled 

 infection studies were also conducted with the object of learning more 

 about the method of transmission of certain diseases in hatcheries. 



