BULLETIN OF THE UNITED STATES FISH COMMISSION, 283 
58.-— THE KEEPING OF SALMONID^ FOE PURPOSES OF EXIIIBT- 
Tiowr. 
By WILLIAM F. SEAL.. 
Exhibitions of live specimens of the salmonidae in aquaria, except 
during the winter months, are so generally attended with great expense, 
from the supposed necessity for a low temperature and the consequent 
use of a large amount of ice, as well as the expenditure of much care 
and labor, that they are considered as not being worth the outlay. Some 
recent experiments at Central Station, Washington, and in connection 
with the exhibit of the U. S. Fish Commission at Cincinnati, have dem- 
onstrated that all the members of the trout family may be kept much 
more easily and at a much higher temperature than has been supposed. 
It is well known that water takes up and retains in suspension atmos- 
pheric air in direct accordance with its temperature. Water is said to 
be capable of holding in suspension for each 16° of lower temperature 
about double the volume of air, so that inversely the expulsion of half 
the volume of air in a given quantity of water would follow a rise of 
16° of temperature. This, then, is the cause of the necessity for keep- 
ing salmonidae at a low temperature— as ordinarily kept in limited quan- 
tities of water not aerated as in nature by tumbling over rocks and falls 
and swirling rapidly about, drawing in large amounts of air — the fact 
that the water does not contain enough air to satisfy their necessities. 
The experiments mentioned consist simply in a change in the method 
of water supply, by which, with the use of a small amount of water, a 
large proportion of air is introduced well dispersed in very minute bub- 
bles, in which shape it is rapidly absorbed by the water. The method 
consists in the use of very fine nozzles of from one-sixteenth to one- 
eighth inch orifice. The point of the nozzle is fixed close over the sur- 
face of the water either straight or obliquely. The stream of water im- 
pinging on the surface of the body of water in the tank, with force, car- 
ries in with it a large amount of air*, which is very minutely divided and 
dispersed, thus keeping the water well charged with air. This of course 
requires force, which is always available where there are systems of 
water-works. Elsewhere it would be necessary to have an elevated 
tank and some means of pumping water thereto to get the necessary 
pressure. An elevation of 20 feet will give sufficient pressure to force 
a one-sixteenth-inch stream of water to the bottom of a body of water 
3 feet deep. A number of such streams might be found necessary, 
varying with the size of the tank, the number or kind of fish, etc. In 
an ordinary-sized aquarium tank, say 18 by 18 by 48 inches, or 24 by 24 
by 48 inches, one, or almost two, streams would probably be found suf- 
ficient. The large amount of air thus constantly forced into the water 
gives the fish the needed supply of oxygen at a comparatively high 
