20 KEPORT OF THE COMMISSIONER OF FISHERIES. 



Suggestion having been made that the method of stripping salmon 

 and trout now practiced at the bureau's stations Avas faulty, a scien- 

 tific assistant was detailed to cooperate with the fish-culturists at 

 Erwin (Tenn.) station in experiments to determine whether the 

 method suggested, in wliich the fish is held in the natural position, 

 belly down, and the pressure applied only back of the ventral fin, 

 was superior to that now employed. It was determined that the 

 established method, when carefully and skillfully applied, is better 

 than that proposed, principally for the reason that less time is re- 

 quired in the operation and the fish subjected to less handling. 



The position of fish-pathologist was filled in February, after a 

 long vacancy, and the new incumbent has been active in investigating 

 the causes of disease and mortality in fishes both in the bureau's 

 hatcheries and in wild waters. Immediate and particular attention 

 was devoted to the high mortality among rainbow-trout fingerlings 

 shipped from White Sulphur Springs (W. Va.) station, and it was 

 practically determined to be due to a protozoan parasite occurring in 

 vast numbers in the intestine. This organism appears to have an 

 unusual life history, and it is still under investigation in the hope 

 that a weak link in its life chain may be found to furnish a point 

 of application for remedial measures. 



Various assistants and collaborators of the bureau have examined 

 into the occurrence and causes of the death of fishes in lakes and 

 streams, and progress has been made in the study of conditions affect- 

 ing the prevalence of parasitism in fishes in natural waters and the 

 possible relation of parasites to retardation of growth in their fish 

 hosts. For a number of years there has been a number of deaths 

 among diamond-back terrapin hatched at Beaufort (N. C.) station 

 and held under the unnatural condition of nonhibemation and winter 

 feeding. This has now been determined to be due to a characteristic 

 bacterial organism, and further studies may develop methods of com- 

 bating the disease. 



STUDIES OF KIVER, LAKE, AND SEA. 



In its investigations of mortality and diseases of fishes, oysters, 

 crabs, etc., and of the causes of sudden or gradual changes in their 

 abundance the bureau has often been baffled by the lack of accurate 

 knowledge of normal physical, chemical, and biological conditions 

 in the waters affected. With the purpose to remedy this deficiency 

 an investigation of Chesapeake Bay was undertaken during the fiscal 

 year 1921. The field work was practically completed in that year, 

 but two supplementary cruises were made in 1922. During the year 

 covered by this report attention has been devoted to the compilation 

 and digestion of the physical and chemical data relating to the waters 

 of the bay and to sorting the biological material preparatory to as- 

 signing it to the specialists for study and identification. 



Kesearch of the same character was begun during the year in Long 

 Island Sound and contiguous waters, where the investigations of the 

 bureau and of the States concerned into the difficult problems pre- 

 sented by the failure of the oyster set have been hampered by lack 

 of information concerning the extent and dissemination of pollutions 

 inimical to oyster culture and fishes and the character of the currents 

 and the distribution of temperatures and salinity of the water. 



