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Aquarium Biochemistry 
EDGAR R. WAITE, F.L. S. 
President, South Australian Aquarium Society 
A Pile of Goldfish Ashore and (right) others Gasping at the Surface of the Water 
Photographs by the Author 
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Most people know that water is com- 
posed of two gases, hydrogen and oxy- 
gen, in the proportion of two to one. 
They also know that fishes breathe in 
oxygen to regenerate their blood, and 
they imagine, perhaps not unnaturally, 
that the fishes obtain it from the combi- 
nation. ‘This they cannot do, for as soon 
as the correct proportion of the two gases 
is disturbed, water no longer exists. 
We must, in the first place, appreciate 
the difference between the chemical ex- 
pressions “mixture” and “combination.” 
Atmospheric air is formed of a mixture 
of two gases, nitrogen and oxygen, and 
we can vary the normal proportion (of 
about 79 to 21), within certain limits, 
without destroying the use of the mixture 
for respiratory purposes. Water, on the 
other hand, is produced, not by a mix- 
ture, but by a chemical combination of 
two gases in certain definite proportions, 
as already mentioned, which cannot be 
upset in the ordinary course of events; 
if the proportions are changed, say by 
means of electricity, resulting in the ab- 
straction of a certain amount of oxygen, 
then twice that quantity of hydrogen is 
also set free, and a corresponding meas- 
ure of water, as such, is destroyed. It 
will be evident, therefore, that fishes can- 
not breathe the oxygen which is a con- 
stituent of the water in which they live. 
Water has the property of absorbing 
and retaining a certain amount of free 
oxygen, this amount varying under dif- 
ferent conditions, especially of tempera- 
ture, the warmer the water the less it can 
hold. Fishes cannot, therefore, live in 
water that has been recently boiled, be- 
cause most of the breathable oxygen has 
been driven off. This boiled water, while 
cooling, will gradually reabsorb atmos- 
pheric oxygen, and the greater area of 
water exposed the more rapidly will ab- 
sorption take place. Hence the process 
