368 U.S. BUEEAU OP FISHERIES 



One of the greatest objections to the use of rearing ponds for trout 

 fingerlings is the cliiRculty of treating the fish should they develop an 

 external infection, such as gill disease. Kemoval of the fish and 

 dipping by the methods now in general use is a laborious process and 

 also results in many fish being severely injured by handling. 



A method of treating fish in pools by allowing a chemical solu- 

 tion to flow into the pools at a uniform rate has been developed by 

 Dr. Fish. The essential part of the device is a floating siphon, 

 the proj)er concentration of the chemical in the pool being obtained 

 by adjusting the strength of the original solution to the volume of 

 flow. This is a very simple device and can be readily adapted to 

 almost any type of pool. In this method the fish are treated for 

 a considerable length of time with a very weak solution, which 

 at the concentrations ordinarily used in the so-called " dipping 

 method ", would prove fatal in a few minutes. 



A very efficient cure for bacterial gill disease has been developed 

 at the Leetown station by Eugene W. Surber. This consists of treat- 

 ing the fish with chlorine gas dissolved in Avater at a concentration 

 of 1 to 2.5 parts per million. Since this solution is quickly fatal 

 to fish, the chlorine must be neutralized by the addition of sodium 

 thiosulphate after 1.5 to 2 minutes. This treatment has been used 

 with great success in circular pools and also in hatchery troughs. 

 It has not yet been tried in other types of pools, but there appears 

 to be no reason why it could not be successfully used wherever 

 there is a rapid circulation of water. 



COOPERATIVE STUDIES OF THE NUTRITIONAL REQUIREMENTS 



OF TROUT 



Investigation of the problems connected with the feeding of 

 trout in hatcheries, which were begun during the summer of 1932, 

 have been continued during 1933 by Dr. C. M. McCay and A. V. 

 Tunison at the Bureau's fish cultural station near Cortland, N.Y. 

 This is a cooperative project conducted under an agreement between 

 the U.S. Bureau of Fisheries, the New York Conservation Depart- 

 ment, and the New York College of Agriculture at Cornell Uni- 

 versity. Special attention has been given to the nutritional prob- 

 lems as well as to the actual feeding experiments, in order to extend 

 our knowledge of the principles of trout feeding beyond that obtained 

 from the Bureau's older experiments of a practical nature in the 

 same field. During the year the hatchery equipment has been altered 

 and improved and electric power is now available. The latter is of 

 considerable importance, since it provides means of controlling the 

 physical environment of the fish that is essential in certain experi- 

 ments and reflects the general tendency in all nutrition laboratories 

 toward a better appreciation of the importance of such control. 



While the work of the investigators was confined as far as possible 

 to the field of nutrition, attention was given to the prevention of 

 disease. Deficieiit diets inevitably lead to disease which may mani- 

 fest itself as a distinct alteration in the anatomy and physiology 

 of the trout, or may result in a secondary invasion of the sick fish 

 by parasites; all of which tends to confuse the results obtained 

 from experiments in nutrition. Moreover, the cure of disease may 

 often lie in the hands of the nutrition student. Hence, the practice 



