36 



MARINE AND FISHERIES 



5 GEORGE v., A. 1915 



which he also searched for the parasite. Fiebiger attributes his failure to find the 

 parasite in the latter species to his not having examined a sufficient number of 

 fish. Assuming that the parasite described by Auerbach ('09, p. 74, 81) is Goussia 

 gadi, as seems probable, it has been found in Gadus aeglefinus on the coast of 

 Norway at Bergen. The coccidian described by J. Miiller ('42) from Gadus callarias 

 is identified by Fiebiger ('08) as Goussia gadi. The parasite found by the writer 

 is also identified as Goussia gadi. The distribution of Goussia gadi is therefore 

 from the Cattegat to the North of Norway, Iceland and Eastern Canada. 



There can be no doubt that the parasites in question, Myxidium bergense 

 and Goussia gadi complete their life cycle in the host fish, in other words there is 

 no intermediate host. Hence their spread occurs only from fish to fish, and a 

 fish becomes infected only by coming into such relations to an infected fish that 

 the spores of the parasite are carried to it from the latter by water currents. This 

 probably means the fairly close proximity of the two fish. The investigation of 

 infectious diseases, where the method of infection is contaminative, has shown 

 that their spread over large areas is almost invariably due to the migration of 

 diseased animals. It is possible that the spread of Myxidium bergense and Goussia 

 gadi over the North Atlantic is due to the migrations of the host fishes in these 

 waters. 



The places mentioned in the discussion of the distribution of Myxidium 

 bergense and Goussia gadi are shown on the map (Fig. 6). 



1^ 



Fig. 6. Map on Mercator's projection showing places mentioned in the sectipn 

 upon geographical distribution. 



The fact that no cysts of Sporozoa were found in the 82 specimens of Pseudo- 

 pleuronectes americanus is interesting. The writer found fifty per cent of the 

 fish of this species caught in the Wood's Hole region in the summer and winter 

 of 1910 infected with Glugea stephani Hagenmiiller. At this time he also found 

 Osmerus mordax from Wood's Hole frequently infected with a microsporidian, 

 apparently Glugea stephani. The twenty-two examples of Smelt Osmerus mordax 

 examined from the St. Andrews region contained no microsporidian cysts. 



