PROGRESS IN BIOLOGICAL INQUIRIES, 19 3 2 141 



stocking this year. Pollution from a pea vinery in 1930 had killed 

 many trout in a section of the stream. 



A study of the food organisms was made above and below the 

 point of pollution. It was found that conditions were approximately 

 the same in both sections of the stream except that may fly and 

 stone fly nymphs averaged much smaller in size in the lower section.. 

 Large slirimp were common in both parts of the stream. From these 

 observations it was decided that recovery was practically complete and 

 that stocking with a limited number of trout might be safely resumed. 



Georgetou-n Lake. — At the request of the Montana Fish and Game 

 Commission, a brief investigation was made concerning the mortality 

 suffered by adult cutthroat trout and grayling in Georgetown Lake. 

 The seriousness of the annual loss in fish at this important spawn- 

 collecting station may be judged from estimates which run from 2,500 

 to 15,000 adult trout and grayling. The cause of this mortahty, 

 which has steadily increased during the last three years, has been 

 attributed to a number of conditions which have been eliminated 

 with no resulting improvement. 



Other duties prevented more than a preliminary investigation at 

 Georgetown Lake. Macroscopic examination of freslil}^ dead speci- 

 mens were made. Approximately half of the trout appeared normal 

 except that the peritoneum was blotched and speckled with bloody 

 areas. Presence of food in the stomach and considerable fat on the 

 viscera indicated sudden death. The remaining trout and all gray- 

 ling examined exhibited reddened areas or vertical red scratches just 

 behind the pectoral fin and in some cases posterior to the dorsal or 

 near the vent which permeated the tissues to a considerable depth. 

 Sex determination indicated that the loss at this time appeared to be 

 almost wholly confined to the females. 



The presence of bacterial infection probably aggravated by crowd- 

 ing and high water temperatures was suggested. A thorough study 

 throughout the following season was recommended. 



Payette Lake. — At the request of the Idaho Fish and Game Depart- 

 ment, a brief limnological study was made of Payette Lake during 

 October to determine the best planting policy for these waters. 

 Consistent stocking with good sized fingerling trout during past years 

 had not shown the anticipated improvement in fishing. 



The usual procedure for study was followed which indicated that 

 Payette Lake is deficient in food production presumably due to lim- 

 ited shoal areas, scarcity of aquatic vegetation, unproductive bottom, 

 and lime deficiency. It was recommended that recently enacted 

 measures protecting the spawning grounds of the principal fishes 

 (redfish, redside cutthroat, and whitefish) be continued and that the 

 redfish and cutthroat be encouraged by artificial propagation. The 

 proposed introduction of bass and mackinaw was condemned in view 

 of the food scarcity and danger to the valuable native fishes. 



MUSSEL INVESTIGATIONS AND POLLUTION STUDIES IN INTERIOR 



WATERS 



The various activities carried forward by the staff headquartered 

 at the University of Missouri, under the direction of Dr. M. M. Elhs, 

 have been grouped under two headings, namely, pollution and mus- 

 sel propagation studies, largely as a matter of mechanical convenience. 



174007—33 5 



