The herald and mail. [volume] (Columbia, Tenn.) 1873-188?, 1877-06-22
Why Fresh Water Fish Cannot Live in
Salt Water.

1t is we'll known that fresh water fish
cannot live in salt water, and tjice ter5G 4;
and it has been supposed that the reason
exists in some poisonous effect which the
inappropriate water exerted. Mr.. Paul
Bert has recently been investigating
this subject, and his conclusion is that
the breath of the creature is not due to-
any toxic action, but is simply phe-
nomt non of osmosis or transmission of
fluids through the membranes. In order
to prove this, it is only necessary to
weigh the animal before and after the
experiment. A frog, for example,
plunged in sea water loses one third its
weight. Ifonly the foot of the frog be
introduced, the blood globules can be
seen to leave the vessels and distribute
themselves under the skin. If an ami
NAL be taken, the skin of which is not
entirely osmotic, the same phenomena
occur in the bronchial system.
There are certain fish, however, which
exist sometimes in salt, sometimes in
fresh water, changing their habitat in
different periods of life or. of the year.
1t, therefore, in view of the above, be-
comes interesting to see how NJ. Bert ap-
plies his discovery to such apparent ex-
ceptions to the general rule. A fresh
water salmon, for instance. plunged ab-
ruptly in sea water, resists the effects
longer than other fresh water fishes; but
he dies within five or six hours. This
shows, according to NJ. Bert, that the
fish never proceed suddenly from fresh
to salt water, but enter brackish water
where the tide ebbs and flows, and live
there a sufficient time to habituate them
selves to the change. This accounts tor
the frequent discovery of large numbers
of the migratory fish in the vicinity OF
mouths of rivers which they ascend.
A fresh water eel, plunged in salt
water does not seem to be affected. But
investigating the peculiarities of this
species M. Bert was led to wrong con
clusion, which may be cited to show how
easy it is, often by pure accident, to
reach an erroneous determination in lab
Oratory experimenting. After having
himself placed several fresh water eels in
salt water, he found as already stated,
that they remained alive and unharmed.
Wishing to continue the experiments, he
directed his assistant to introduce the
fish and report results. To his surprise
the eels then persistently died after a
three or four hours sojOurn in the salt
water, and long search failed to discover
the reason why it was that when Nj.
Bert placed them i'll the tanks they lived,
while when the assistant did so they per
ished. Finally, NJ. Bert found that the
assistant, doubtless on account of the
slip2eriness of the eels, lifted them with
a piece of cloth in his hand. The cloth
rubbed eff little of the original slime of
the animal, which protected it from the
n IL IL
denuded portion, and the eel eventually
died.
The converse experiment, of inserting
sea fish in fresh water, produced analO-
gus results. The gills were the seat of
alterations, the same as those noted in
fresh water fish placed in salt water. NJ.
Bert also observed that the life of the sea
fish could be prolonged by adding salt to
the fresh water, thus adding further con-
frmation to his theory. Scientific Anacr-
icdn.