52 MEMOIRS OF THE QUEENSLAND MUSEUM. 
Superficially the water in the aquaria gives little indication of impending 
tragedy, and it is not until the fish begin to suffer disintegration of the 
abdominal contents that the abnormality becomes distinctly noticeable, the fish 
resting motionless on the bottom of the tank. Now and again, as if to cast off 
the discomfort occasioned thereby, a fish will make a sudden dart through the 
water only to come to rest again with extreme suddenness, this action seems 
to denote a final stage in the development of the disease. 
It is I think recognised that it is desirable from time to time to replace 
the chemicals in the water which are used up during the healthy life of the 
fish, and small quantities of magnesium sulphate and sodium chloride materially 
assist towards this end, whilst the addition of plaster of paris provides for a 
possibility of calcium deficiency. In this instance the use of plaster of paris 
arrested the disease. 
The readiness with which the CaS0 4 is dissolved in “ spent” aquaria 
containing an undue accumulation of carbon dioxide as the result of the 
presence of putrefying substances in the water, followed by a period of rapid 
oxygen consumption, suggests the necessity of such chemicals. Soon after the 
calcium sulphate is added to the water, precipitation takes place and the 
water, becoming wonderfully clear, provides an improved environment for the 
fish themselves, which soon react to the changed conditions. As soon as an 
equilibrium has been reached, the CaSOr may be removed, but by this time a 
higher alkalinity has been reached. Now although our larvivorous fish will live 
in slight acidity, say pH 6‘0, nevertheless it is a matter of frequent comment 
that they do so only under protest, and that they seem more prone to disease 
than they do in alkaline waters. The acidity of the water seems to synchronise 
also with the slow but sure destruction of the snails ; Bullinus pectorosus 
Conrad and Limncea lessoni Desh. do not seem to thrive in such a medium.— 
R.H.H. 
Pathology of the Disease. 
Three fish were examined post-mortem. The pathological findings 
resembled very closely those found in cholera in the human ; they were as 
follow : — 
There was constantly a deep bile-tinged staining under the skin of the 
abdomen just ventral and caudal to the left pectoral fin. One specimen showed 
necrosis of the body wall at the site of the staining, the skin being thinned, 
of the texture of tissue paper, and was about to slough. There were no other 
external features of interest. On opening the body, the respiratory system 
I found to be, as far as I could judge, normal. 
On examination of the abdominal contents, I found practically the whole 
of the intestines involved in a gangrenous process, only about a centimetre of 
the terminal portion escaping. The bile channels were also involved, leading to 
rupture and consequent staining of the abdominal wall, as noted above. I 
could not judge macroscopically whether the liver was involved. In two 
specimens, the necrotic process had spread to the swim bladder, which no 
