FRESHWATER FISH EPIDEMICS IN QUEENSLAND RIVERS. 205 



presence of similar organisms, so they may be disregarded as 

 direct causes of the mortality. Those met with have been 

 already described by us (J. & B. 1918). 



Lymphosporidium truttce, a member of the Haplosporidia 

 and a parasite of the lymph system, was described by Calkins 

 (1900) as a cause of an epidemic amongst trout. {See also Hofer, 

 p. 60 ; Doflein, p. 934.) Another member of this Sporozoon 

 group, Ichthyosporidium sp., near I. gasterophilum Caull. & 

 Mesnil, has been recorded by Robertson (1909) as fatal to 

 sea- trout. 



(ii) Protozoa — Infusoria and Flagellata. 



The chief ciliate parasites harmful to freshwater fish are 

 Ichthyophthirius, Chilodon, and Cyclochoita. The first-named 

 causes epidemics in aquaria (Hofer, pp. 122-7). The other two 

 appear to be of less importance. 



Of the Flagellata, Costia is said to cause at times heavy 

 mortality amongst salmon fry in Austria (Franke, 1910 ; 

 Hofer, p. 115). 



None of these protozoa except an occasional Cyclochceta 

 was detected during our examinations of Queensland material, 

 whether diseased or not. 



(c) Fungi as a Possible Cause. 



As a result of our examination of fish dead or dying from 

 the disease, we found the fungus Saprolegnia constantly 

 present, either on the general body-surface (including fins and 

 tail) or on the gills, or even on both situations. A similar 

 finding was reported by one of us (Johnston, 1917) when 

 deahng with a specimen previously sent down. In addition to 

 the records of Australian occurrences contained in that paper, 

 there is a short one b}^ Waite (1894), who mentioned finding 

 the fungus on Ctenolates ambiguus Richdsn. (= Pledroplites) . 

 Further references to the disease and to literature relating to 

 it can be found in papers by Hofer (1906), Clinton (1893), and 

 Johnston (1917). 



It was previously regarded as the cause of the salmon 

 disease, but it is now recognised that the fungus is secondary 

 and is capable of readily exchanging a saprophytic mode of 

 existence for a parasitic one, should it have an opportunity. 

 Such would be given by injuries as well as by the presence of 

 external conditions or diseases which interfere with normal 

 Q 



