60 American Fisheries Society 



ternal epithelium, which produces a cyst enveloping the glo- 

 chidium. Under normal conditions the young mussel re- 

 mains encysted long enough to pass through a metamor- 

 phosis after which it drops from the fish in a form closely 

 approaching the adult. 



A little experimentation shows that, taken a given species 

 of mussel, all fish are not equally susceptible. Some do not 

 readily receive the glochidia, others quickly shed them, 

 while others die from excessive infection. Thus we have 

 in certain instances what has been called an immunity at 

 least to a given mussel species. Lefevre and Curtis find 

 immune to the glochidium of Lampsilis such fishes as the 

 German Carp, certain minnows and darters. 



Acting upon the information obtained from such experi- 

 ments the Bureau has carried on practical work in mussel 

 propagation. Fish in large numbers are infected and re- 

 leased to spread the mussels in whatever waters they may 

 reach. This work, however, has been limited to a few 

 species of the Lampsilis group, chiefly Lampsilis ligamen- 

 lina and L. anadontoides. With one possible exception none 

 of the Ouadrula group of mussels, including some of the 

 most valuable commercial shells, had up to the time of the 

 present investigation, been carried through the parasitic 

 stage. Many experiments had been made on various species 

 of fish and under varied conditions to determine a suitable 

 method of propagation. The rarity of successful infections 

 and other results would suggest that as in other cases of 

 parasitism in the animal and vegetable kingdom each mussel 

 may have its appropriate host or hosts restricted to a species 

 of fish, a genus or a family as the case may be. Since the 

 number of species of mussel for this locality is forty or 

 more and the number of species of fairly common fish at 

 least sixty, the problem of determining the appropriate 

 host for each mussel is obviously quite complex. To deter- 

 mine the hosts for each species of mussel by artificial infec- 

 tion, a "trial and error" method would be very difficult. 



