FRESHWATP:R PISII epidemics in QUEENSLAND RIVERS. 201 



carbon dioxide can quickly develop " (Shelf ord and Powers, 

 1915, p. 322). No doubt, in the case of the Queensland epidemics 

 HgS has played an important role in aggravating the condition, 

 though it probably did not cause it in the first place. 



Ammonia is very toxic to fish and is apparently not 

 recognised by them, as they do not react in such a way as to 

 avoid it when given the opportunity (Wells, 1915a). 



The reactions and resistance of fishes in their natural 

 environment to salts were studied by Wells (1915b), who used 

 the chloiides, nitrates, and sul_ hates of the commoner bases — 

 e.g. sodium, ammonium, potassium, calcium, and magnesium.^ 

 He found — (1) that freshwater fish reacted to their presence in 

 solution but were not as sensitive to salt ions as to H and OH 

 ions ; (2) that they reacted to combinations of antagonistic 

 salts or salt and acids in a manner which tended to bring 

 them into a region of optimum stimulation ; and (3) that 

 rhythmic alterations in metabolic activity in the case of 

 anadromous fish (such as salmon) were correlated Math their 

 migrations . 



Powers (1917) has studied the relative toxicity of the 

 chlorides and nitrates of the alkalies and alkaline earths, as v/cll 

 as various other substances, on goldfish. He pointed out that 

 it is improbable that toxicity of a substance is due to osmotic 

 pressure. 



Reduction in salinity as a result of flood-waters being 

 turned aside to cover certain Japanese reefs^** led to very great 

 destruction of marine algse and the associated fauna. 



4. Poisons as a Possible Cause of the Epidemic. 



Apart from the toxic effects likely to be caused by the 

 agencies referred to in the last section, one can probably 

 dismiss the possibility of the mortahty being caused by a 

 poison — e.g. one of plant or mineral origin — on account of the 

 wide area involved, the different flora in each region, the 

 different types of water, and the character of the outbreaks. 



^ Whetmore (1918) in his investigations regarding the epidemic 

 amongst wild ducks in Utah, U.S.A., proved that it was due to alkaU 

 poisoning, especially by the chlorides of calcium and magnesium which 

 are brought to the surface of the soil of the swamps by capillary attraction. 



loYendo, Econ. l^roc. Roy. Dublin Soc, 2, 1914, pp. 105-122 (not 

 available). (See aZsop&'.ors by Sumner (Bull. Bur. Fisheries 25, 1905(1906) 

 pp. 53-108) and Scott ~d IS, 1908 (1910), pp. 1145-1150) regarding the 

 effects on the blood o\ is 'i 5S "^f r-.hanges in salinity and density of water. 



