PKOGRESS IN BIOLOGICAL INQUIRIES, 1923. 23 



An outbreak, iii the bureau's aquarium, of the disease caused by 

 Ichthyophthirius, provided a favorable opportunity for studies on 

 the life history of the parasite and methods of control. These in- 

 vestigations were carried on by H, F. Prytherch, scientific assistant, 

 who found that alum sulphate possesses certain advantages over 

 chemicals previously used in the treatment of the disease. A brief 

 bulletin on the disease is being prepared. 



An outbreak of a " gas bubble " disease in developing trout at 

 La Crosse, Wis., was investigated by the Fairport station. The dis- 

 ease was found to be characterized by the diffusion of yolk through 

 the surrounding tissues and in some cases by the formation of a 

 bubble of gas in the yolk. Since it was known that there was an 

 excess of carbon dioxide dissolved in the water, it was suspected 

 that this was the primary cause of the trouble. This diagnosis was 

 borne out by the fact that elimination of the gas before the water 

 entered the troughs caused a disappearance of the abnormal condi- 

 tion although the fish affected failed to recover. 



At the invitation of the Minnesota State Game and Fish Commis- 

 sion an investigation was made of the mortality of pike perch at 

 Cut Foot Sioux, Minn. The fish found dead had apparently been 

 trapped some weeks before for the collection of eggs and, owing 

 to improper handling, had been scratched and bruised, resulting 

 in a fatal infection with Saprolegnia. 



In June a severe mortality of crappie and sunfish in Lake Poke- 

 gama, Minn., was investigated by R. L. Barney, director, and H. O. 

 Hesen, superintendent, of the Fairport station. The cause of the 

 mortality was diagnosed as a heavy infestation of the gills by the 

 worm Dactylogyrus with a secondary bacterial infection that usually 

 killed the fish. This mortality at Pokegama is of particular in- 

 terest in view of its regular annual occurrence in May and June 

 for the past 15 years. Its original appearance seems to have been 

 connected with the lowering of the water level of the lake by the 

 blowing out of a dam, which resulted in cutting off a broad con- 

 nection with Snake River. The mortality affects several species of 

 fish, but the crappies and sunfish suffer most severely. 



During June a heavy mortality of gizzard shad occurred in lakes 

 in the suburbs of Des Moines, Iowa, and at the invitation of the 

 State game warden an investigation was made by the Fairport sta- 

 tion. The disease was characterized by inflation of the pectoral fins, 

 and the study of sectioned material led to the conclusion that it 

 was due to bacterial infection, probably by a gas-forming organism. 



At the request of Representative Sweet, of Iowa, an investigation 

 of conditions in the Iowa River was made by C. N. Blystad, of 

 the Fairport station. A serious mortality of fishes occurred in this 

 river during the late fall and early winter, and although fish were 

 not dying at the time of the investigation it Avas possible to gather 

 sufficient data to warrant a definite conclusion as to the cause. 

 It was found that the mortality was due to large amounts of chemical 

 and organic wastes allowed to pass into the stream from a sugar fac- 

 tory located on the river. 



PHYSIOLOGY AND XL'TKITIOX OF FISHES. 



Prof. A. S. Pearse, of the University of Winconsin, and his gradu- 

 ate students continued their studies on the physiology and nutrition 



