SOME CASES OF NARROWLY RESTRICT- 

 ED PARASITISM AMONG COMMERCIAL 

 SPECIES OF FRESH WATER MUSSELS 



By Dr. A. D. Howard, 

 U. S. Bureau of Fisheries, Fairport, Iowa. 



The U. S. Bureau of Fisheries has now carried on for 

 some six years an investigation of methods of propagat- 

 ing fresh-water mussels. 



The work has gone on beyond the experimental stage 

 and operations have been conducted upon a scale that it 

 is hoped will appreciably increase the supply for com- 

 mercial purposes. 



While certain species of mussels have been successfully 

 dealt with by the methods first adopted, difficulties have 

 been experienced with other species. In a paper read 

 before the American Fisheries Society in 1912 I showed 

 that I had been able to propagate the Warty-back Mussel 

 on the catfish and that apparently they could not be 

 reared on other species. From my studies of natural in- 

 fection it looked to me at that time as if other cases of 

 restricted parasitism would be found. The subject of 

 natural infection has been made the object of special 

 study at the Fairport Station and some considerable data 

 published showing the species of fish on which the vari- 

 ous mussels have been found. The data thus obtained 

 have in some cases pointed conclusively to definite results 

 while in others the interpretation was less obvious. 



The identification of the larvae (glochidia) when im- 

 bedded in the tissues of the host is uncertain in some 

 forms, and accidental infections of a temporary nature 

 undoubtedly occur. This makes necessary some method of 

 proving out. In practice I have taken the indications 

 obtained from observation of natural infections as a 

 guide and made a test of the suspected species, comparing 

 other species as a control. As the object of the inves- 



