586 XJ. S. BUREAU OF FISHERIES 



interesting facts lirought to lijilit in this phase of tlie work is tliut the small 

 bivalves belonging to the genus Pisidium occur in considerable uuuibers in some 

 of the very soft water lakes, where the water has a pH of 5.2 and onlj- 0.15 

 milligram of calcium per liter. 



Specimens of leeches were obtained from 38 lakes, but no thorough survey 

 of the leech population was made on any of them. A total of 18 different species 

 was represented in the various lakes. 



In the study of the external parasites of the fish, 1,300 specimens belonging 

 to 11 different species of fish were examined. Of this number only 28 speci- 

 mens, or a little more than 2 per cent, harbored parasitic copepods. The 

 largest number of these parasites found on a single fish was about 20 Ergasilus 

 on a rock bass from Allequash Lake. Most of the other 27 parasitized speci- 

 mens carried onl.v a small number of the copepods, two or three up to a dozen. 

 Only two forms of parasitic copepods were found on these fish and both of 

 them represent new species. A report on them is now ready for publication. 

 Leeches were found on only 10 of the 1,300 fish examined. 



Over a thousand fish were examined for internal parasites ; of this number 

 657 were yellow perch, 166 ciscoes, 170 rock bass, and a small number of speci- 

 mens belonging to two or three other species. The different species of fish 

 showed very marked differences in tlie percentage of infestation in the various 

 lakes.. In the ciscoes, for example. 66 per cent of the specimenis from Muskel- 

 lunge Lake were free of internal parasites while only 8 per cent of those 

 from Silver Lake were not parasitized. Only 3 per cent of the yellow perch 

 from Muskellunge Lake gave negative results, while almost 98 per cent of 

 those from Weber Lake were negative. Specimens of rock bass from three 

 lakes (Muskellunge. Nebish and Silver) were examuied and all of them were 

 parasitized. Also the smallmouth black bass were found to be heavily para- 

 sitized in Nebish and Silver Lakes. The parasites belonged to four different 

 groups, namely, Myxosporidia. Trematoda, Cestoda. and Acanthocephala. 



During the present academic year (1930-31) 5 research assistants are working 

 on the material that was collected during the summer of 1930 and in previous 

 summers ; 3 of these assistants are chemists and 2 are biologists. One of the 

 chemists is making quantitative deteiininations of the organic carbon and 

 organic nitrogen in the lake residues, another is making a similar study of 

 silica and calcium, while the third is working on magnesium and hydrocarbons. 

 One biologist is counting the organisms in the net and centrifuge plankton 

 catches, and tlie other is studying the scales of the yellow perch in order to 

 determine the rate of growth of this fish in different lakes. 



At the present time (December, 1930) five different reports on various 

 phases of the work are practically ready for publication ; at least four of thenj 

 will be published before the 1st of July, 1931. 



PACIFIC COAST AND ALASKA FISHEBY INVESTIGATIONS 



On November 1, Dr. Willis H. Rich who, in conjunction with the 

 late Dr. Charles H. Gilbert has planned and directed the scientific 

 work of the Bureau of Fisheries in Alaska for the past several years, 

 resigned from his position as director of Pacific Fishery Investiga- 

 tions to become a member of the faculty of Stanford University. 

 The bureau hopes to continue to have the benefit of his experience 

 and advice in the future. J. A. Craig is now acting director of the 

 Pacific coast laboratory. 



No new investigations have been initiated during 1930. All of 

 the previously planned programs have been carried out, and satis- 

 factory progress has been made. These investigations have as their 

 objective the solution of biological problems related to the conserva- 

 tion of the fisheries of Alaska. 



ALASKA SALMON 



Tagging experiments. — The salmon-tagging experiments, which 

 have been carried on in Alaska since 1922, were continued during the 

 season of 1930. Approximately 3,500 tags were attached. About 



