204 PROCEEDINGS OF THE ROVAL SOCIETY OP QUEENSLAND. 



A careful examination of a considerable number of affected 

 and healthy fish, cliiefly from the Thomson River, revealed the 

 presence of many species of Gyrodactyloid trematodes infesting 

 the gills in both cases, so that invasion by the minute parasites 

 can at most be only a contributing factor and not the cause 

 of the outbreaks. 



Tliough an examination of the viscera revealed the pre- 

 sence of digenetic trematodes, various nematodes and echino- 

 rhynchs, as well as occasional cestode larvae, none of these can 

 be incriminated. The marked fatty degeneration of thc^ 

 viscera has already been mentioned. 



(b) Protozoa as a Cause. 

 (i) Sporozoa. 



Of the Sporozoa the most important groups in the present 

 connection are the Myxosporidia and the Microsporidia. It 

 is well Icnown that some species give rise to epidemics amongst 

 freshwater fish, while many produce lesions resulting in the 

 death of the host, though an epidemic may not follow. The 

 best loiown is Myxobolus jjfeijferi Thel., wliich at times brings 

 about a tremendous destruction of barbels in the Moselle, 

 Rhine, Meuse, Marne, Aisne, and Seine. Full accounts of this 

 Myxobohasis are given by Hofer (1906, p. 71) and Gurley 

 (1894, p. 227), in whose Avorks further references to literature 

 are to be found. The fatty degeneration which takes place as a 

 result of that disease reminds one somewhat of the condition 

 commonly associated with the Australian outbreaks, but the 

 " boil formation" so common in the barbel disease is not 

 manifested in our epidemics. Though some observers have 

 referred to the presence of a bluish swelling on the under side of 

 affected fish, it is not a constant feature and is certainly not of 

 the type associated with the European epidemics. A dis- 

 inteo"ration of muscular tissue of fish is also caused by certain 

 other Sporozoa — e.g. some species of Chloromyxum and Glugea 

 {G. destruens Thel.). 



Though some of the diseased fish first examined by us were 

 found to be parasitized by Myxosporidia, belonging to the 

 genera Myxobolus, Myxosoma, Myxidium, and Henneguya, and 

 occurring in various organs such as the gills, gall-bladder, and 

 kidneys, yet a search through healthy material showed 1he 



