Canfeld. — Fresh Water Mussel. 173 



mercial mussels. In the slides that will be thrown on the screen later, 

 a number of host fishes will be shown. Such fish as the black bass, 

 crappie, sunfish, sauger, perch and pike are very useful hosts in carry- 

 ing what is known as the river mucket and the Lake Pepin mucket, two 

 of our most valuable button-producing shells. The sheephead is the 

 only known carrier of the butterfly mussel, another very good commer- 

 cial mussel. Then, such fish as the yellow perch also carry the mucket, 

 and catfishes carry the Quadrula mussel, the exterior of which is rougher 

 than that of the other types. The two main groups are the Lampsilus 

 group and the Quadrula group; most of the Quadrulas are carried by 

 catfishes and other lake fishes. 



Mr. Pope: Is it possible to raise mussels from the glochidia stage 

 to the adult stage without the intervention of a host? 



Mr. Canfield: There is just one mussel we know of that produces 

 an adult without its passing through a state of parasitism on fishes, 

 and that is known as the squawfoot mussel, which is of no commercial 

 value. There is, however, some question about that; it is also known 

 that the squawfoot mussel uses fishes as hosts. 



Mr. Pope: Has it ever been established whether the encysting of 

 glochidia in the fins or gills of fish is for the purpose of protection, or 

 for the desire for food? 



Mr. Canfield: Dr. Avery, as I understand it — I may be speaking a 

 little in advance, as he has not yet published his paper on the subject- 

 has very definitely shown that the mussel consumes food from fish. 

 I presume he would not object to my making the statement, although, 

 as I say, he has not yet published the results of his researches. 



Mr. Pope: Do you believe that the encysting is for the purpose of 

 obtaining suitable food? 



Mr. Canfield: I am satisfied from the slides which Dr. Avery 

 showed me — it is entirely his work, not mine — that the mussel consumes 

 a portion of the fish. In fact, the part that the tiny larval mussel bites 

 on to is eaten, if you can express it that way, by the cells during the 

 time that the larval mussel is passing through the metamorphosis. 



Mr. Pope: Has the Bureau of Fisheries ever carried on any ex- 

 periments to determine whether it is possible to raise glochidia to adults 

 4vithout the intervention of a host fish? 



Mr. Canfield: Yes. but so far, all have been unsuccessful. 



Mr. Avery: Experiments in that line are still being conducted? 



Mr. Canfield: Oh yes. 



Mr. Pope: What percentage of adult mussels have been known 

 actually to develop from glochidia encysted upon fish? 



Mr. Canfield: You have asked me a difficult question. I do not 

 think we have any figures on that. 



Mr. Pope: What percentage would you suggest? 



Mr. Canfield: I should think that if we got one in a thousand to 

 maturity, we would be doing very well. 



