FRESHWATER FISH EPIDEMICS IN QUEENSLAND RIVERS. 19r> 



Distilled water has been shown to be toxic to various 

 organisms owing to its influence on the permeability of the gill 

 membranes, leading to the loss of salts by the animal and the 

 absorption of water by osmosis (Abbot, 1913). Such water was 

 found by Wells (1915, pp. 241, 254) to be not toxic if rendered 

 slightly acid, but remained so if made slightly alkaline. 



The following extract from Wells's paper (1915, pp. 243-4) 

 is of interest : — " The fact that in natural bodies of water the 

 chemical reactions of the water may vary from alkalinity 

 through neutrahty to acidity, or the reverse, makes he practical 

 importance of a knowl?dg3 of the reactions and resistance of 

 fishes and other organisms to such chemical conditions an 

 obvious one. From the experiments (referred to in his paper) 

 it is clear that water which giv^s an alkaline reaction to 

 phenolphthalein for any length of time during the year is 

 undesirable as a home for most freshwater fishes. On the 

 other hand, marine fishes with the exception of anadromous 

 species would probably not survive in water which was even 

 faintly acid. Since algae or other phytoplancton forms may 

 cause a body of water to become wholly or partly alkahne, 

 through their abihty to dissociate the bicarbonates, vegetation 

 in fish waters assumes a line of importance heretofore little 

 considered. The effects of sewage upon the acidity or alkahnity 

 of natural bodies of Avater must be reconsidered in the light 

 of its possible injurious or beneficial effects due to its chemical 

 action. . . . Henderson's work (1913)^ on the mechanism 

 which maintains a constant proportion of H and OH ions :n the 

 blood of animals, suggests the physiological reason for this 

 extreme sensitiveness of the fishes. Very small variations in 

 the proportions of these two ions in the blood of the organism 

 are of grave importance and we find in the blood a combination 

 of gases and salts that makes such variations impossible as long 

 as the animal is normal. The blood will maintain its normal 

 chemical reaction (just on the alkaline side of neutrahty) in the 

 face of relatively large changes in the environment, yet we 

 know that the mechanism breaks down when the change is either 

 too gr at or too long continued. . . . The hypersensitiveness 

 of the animals to the chemical reaction of the water 

 in the case of aquatic organisms is another important factor 

 in preserving the normal reaction of the blood, as the reactions 



^ L. .J. Henderson, The fitness of environment. McMillan, New 

 York, 1913. 



