68 American Fisheries Society 



osteus osseus, Linnaeus, and the dogfish, Amia calva, Lin- 

 naeus. In some cases the immunity seems to extend to 

 large groups of fishes as for example the Catostomidae 

 (suckers). The Catfishes have been regarded as belonging 

 among the immune fishes, this opinion being based largely 

 on the results of artificial infection experiments. 



In my examination of catfish the results have been 

 largely negative, especially in the spring catches, but on 

 fish caught during July and August I found natural infec- 

 tion. The first of these on Ictalurus punctatiis, the channel 

 cat, and the second on Lcptops olivaris, the flathead. The 

 species proved to be Quadriila pustnlosa, the pimple-back, 

 a common shell of this locality and of considerable impor- 

 tance commercially. 



To test for methods of "artificial propagation" I made 

 infections with three species of catfish and two other kinds. 

 The following were employed: Amciurus melas, bullhead, 

 Lcptops olivaris, flathead and Ictalurus punctatiis, fiddler. 

 Pomoxis annularis, crappie and Lcponiis pallidas, sunfish. 

 When exposed to infection in the same tank and thus under 

 the same conditions, the difference in susceptibility between 

 the catfish and the other species was very marked and the 

 difference in implantation still more so. The catfish retained 

 the glochidia ; while though abundant on the gills of the 

 crappie and sunfish, they disappeared the second day. Ex- 

 periments to determine the optimum infection were under- 

 taken and a count of eight hundred made upon one fish. In 

 this experiment the fish showed no discomfort nor any signs 

 whatever of impaired vitality, however at the present time 

 the optimum for the mussel has not been determined. 



Later observation on natural infection in Ictalurus punc- 

 tatus has yielded further confirmatory evidence that this 

 species is the natural host for Quadriila pustulosa. The 

 glochidia in these cases showed an advanced stage in the 

 metamorphosis of the young mussels in which two adductor 

 muscles are apparent and considerable growth beyond the 



