24 U. S. BUREAU OF FISHERIES. 



is published in response to the frequent demands upon the Bureau 

 for information of the character furnished by it. 



FRESH-WATER MUSSELS. 



The Bureau continued the propagation of fresh-water mussels and 

 investigation of problems affecting the mussel industries. The num- 

 ber of glochidia infected upon fish and liberated in the public waters 

 was substantially greater than in the preceding year, and the unit 

 cost per thousand correspondingly lower. The results of artificial 

 propagation are detailed in another report.* 



EXPERIMENTAL WORK. 



Notable results were obtained in the experiments conducted at the 

 Fairport station in rearing young mussels. The methods of arti- 

 ficial propagation, as regularly practiced, consist in liberating the 

 fish immediately after infection, so that cultural operations are not 

 involved. In the effort to improve upon the established practices, 

 experiments have been conducted during several seasons in retaining 

 infected fish during a period of two or three weeks, until the juvenile 

 mussels are liberated, and then holding the young mussels, which at 

 first are of microscopic dimensions, until they have attained a size 

 (say one-half an inch in length) permitting of their being handled 

 with convenience and planted deliberately upon bottoms which are 

 known to be suitable. Simple as the task is in the stating, peculiar 

 difficulties are encountered, and its accomplishment had baffled all 

 previous attempts in this country and elsewhere. Before the past 

 year a measurable degree of success had been attained at Fairport 

 with one species of mussel (the Lake Pepin mucket). During the 

 summer of 1919, the experiments conducted by Dr. F. H. Eeuling led 

 to the rearing of two additional species (yellow sand-shell and river 

 mucket) in considerable quantities in small troughs supplied with 

 naturally clarified river water. 



Experiments having a somewhat similar object were conducted in 

 Lake Pepin by Roy S. Corwin, scientific assistant. Here young mus- 

 sels originating from artificial infections were reared in considerable 

 quantities within inclosures on the bottom of the lake in relativeh^ 

 shallow water. Other experiments conducted at this place gave indi- 

 cation that glochidia carried over in the marsupia from the preceding 

 year endured a shorter period of parasitism than those taken from 

 the marsupia in the same season in which the eggs were deposited. 



Dr. L. B. Arey, of Northwestern University Medical School, investi- 

 gated the relations of glochidia to host as regards attachment and 

 encystment, and the results of his investigations have been submitted 

 for publication in another place. 



PROTECTION OF MUSSELS. 



In January, 1920, at La Crosse, Wis., the Bureau participated 

 with officers of the Wisconsin Conservation Commission and the 

 Minnesota Fish and Game Commission and other interested persons 



.« Smith, Hugh M. : Report, U. S. Commissioner of Fisheries, 1920. Washington, 1920. 



