CNIDOSPORIDIA, MYXOSPORIDIA, ACTINOMYXIDIA 305 



has its special site of infection in one to several species of fish. 

 The gills and gall bladder are most frequently parasitized by 

 Myxosporidia in freshwater fishes, while the gall bladder and 

 urinary bladder of marine fishes harbor one or more species of 

 Myxosporidia. When the infection is concentrated in the fins or 

 integument, the resulting changes are quite conspicuous (Fig. 

 129). The infection in the gills is usually manifest by whitish 

 pustules which can be frequently detected with the unaided 

 eye. When the wail of the alimentary canal, the mesentery, 

 liver, and other organs are attacked, one sees considerable 



Fig. 129 External symptoms of myxosporidian infection in fish. (After Kudo), 

 a. Head of the short-headed red-horse, Moxostoma breviceps, showing the 

 cysts of Myxobolus conspicuus. One-half natural size. b. A blunt-nosed min- 

 now, Pimephales notatus, showing three tumors which were caused by Myxo- 

 bolus notatus. Five-eighths natural size. c. A sucker, Catostomus commersonii, 

 with a large tumor due to an infection by Myxosoma catostomi. About one- 

 third natural size. 



changes in them. Heavy myxosporidian infection of the gall 

 bladder or urinary bladder of the host fish may cause abnormal 

 appearance and coloration or unusual enlargement of the organ, 

 but under ordinary circumstances the infection is detected only 

 by a microscopical examination of its contents. 



