FRESHWATER FISH EPIDEMICS IN QUEENSLAND RIVERS. 187 



in the Severn (Dumaresq) and Mclntyre Rivers on the southern 

 border of Queensland. These rivers rorm part of the Barwon or 

 Darling River system. Three rivers flowing east f om the 

 Great Dividing Range were affected though not very seriously — 

 viz., the Brisbane and Mary in the A^inter of 1917 and the 

 Burnett in 1918. 



We may note that the outstanding features of the epidemic 

 w^ere as follows : — 



(a) The species especially affected were the golden 

 perch or yellow-belly {Plectrojylites ambiguus), 

 the freshw'ater black bream or grunters {Therapon 

 spp.), Murra}^ cod or perch (Oligoriis macquarlce), 

 and bony bream {Nematalosa elongata), and jeAV- 

 fish or catfish (various species of Siluridce). 

 {b) It usually occurred during the colder and drier 

 portion of the year, July and August, though 

 sometimes earlier and often persisting later. 

 (c) The water Avas nearly always stagnant and the 

 epidemic ceased suddenly, after heavy rains had 

 caused the rivers to flow. 



{d) The affected fish Avere always fat ; they became 

 lethargic, sAvam sIoavI}- at the surface of the Avater, 

 and died. A bluish colour Avas commonlj^ seen 

 in the mouth region. 



POSSIBLE CAUSES. 



1. The use of dynamite or other explosive. 



2. Chmatic — 



(a) Dry AAeather ; 

 (6) LoAv temperature. 



3. State of the Avater — 



(a) Physically, i.e. presence of suspended matter or 

 Aveeds AA'hich might clog fish-gills ; 



(6) Ciiemically, e.g. excess of carbon dioxide, defi- 

 ciency of oxygen, acidity or alkalinity, etc. 



4. Poisoning due to the presence of some toxic subs+ance 

 in the Avater. 



5. Overstocking and consequent ^tarA^ation. 



