PROGRESS IN BIOLOGICAL INQUIRIES, 1935 445 



many, and present efforts are directed towards the determination of 

 the maximum concentration of each ])racticable disinfectant toler- 

 ated by trout, and the minimum disinfecting concentration eifective 

 against each type of pathogenic organism. The eventual goal of 

 the disease prevention investigations is the development of a tech- 

 nique involving the use of some disinfectant, or combination of dis- 

 infectants, which may be applied under ordinary hatchery conditions 

 with a minimum of effort and which will prevent the appearance of 

 most, if not all, diseases of hatchery trout and salmon. 



Another research project of this laboratory concerns the epidemi- 

 ology of fish diseases — likewise a new field of endeavor. Through 

 the generous cooperation of the Division of Fish Culture, daily loss 

 records are kept on individual lots of fish by all hatcherymen in the 

 intermountain and Pacific coast regions. An accurate loss record 

 is thus available for every lot of fish from the time they are brought 

 to a hatchery until they are finally liberated. Over a period of time, 

 an analysis of these records should not only yield reliable informa- 

 tion concerning the efficiency of individual hatcheries, but should 

 likewise demonstrate many of the factors responsible for losses, and 

 the exact effect of efforts to correct these factors. Such information 

 should prove of great value in raising the efficiency of the entire 

 system of artificial propagation of trout and salmon. 



During the year, studies were undertaken on the relative steriliz- 

 ing power of the various disinfectants commonly used at hatcheries. 

 For such studies, a modified phenol coefficient technique w^as em- 

 ployed and a strain of Bacteriicm salmorucula was chosen as the test 

 organism. It was indicated that any concentration of these disin- 

 fectants capable of killing B. solmonicida during an exposure of 

 1 hour was likewise fatal to fish life in the same period of time. A 

 concentrated solution of calcium hypochlorite proved to be the most 

 satisfactory disinfectant for sterilizing ponds not containing fish 

 and for nets, dippers, and other hatchery utensils. 



The more basic pathological studies on individual diseases of fish 

 were continued during the year. A previousl}^ unrecognized type of 

 gill disease, of similar pathology but different etiology than the bac- 

 terial gill disease common to eastern United States, was found affect- 

 ing both trout and salmon at several western hatcheries. This dis- 

 ease was apparently of bacterial origin, and although several organ- 

 isms w^ere isolated in pure culture from infected gill tissue, suitable 

 opportunity for experimental infections has not yet been available. 

 Until such experiments are accomplished it is impossible to state 

 W'hich one, if any, of the cultivated organisms is responsible for the 

 disease. This western variety of gill disease has failed to respond 

 favorably to any known form of treatn:ient. Apparently by the time 

 the presence of this disease is realized, the host is so weakened through 

 extensive tissue alteration that it is unable to withstand the addi- 

 tional rigors of treatment. 



In addition to the definite long-term projects summarized above, 

 numerous field trips have been made to assist the hatchery men with 

 their disease problems. 



A new disease known as "white mouth", affecting tropical fish in 

 the Southern States, was found to be due to infection with Bacillus 



