The daily gazette., 1877-06-27
WHY FRESH WATER FISH CAN
NOT LIVEIN SALT WATER.

1t is well known that fresh-water
fish cannot live in salt water and vice
versa; and it has been supposed that
the reason existed In some poisonous
effect which the inappropriate water
exerted. M. Paul Bert has recently
been investigating this subject aad his
conclusion is that death of the crea-
ture is not due to any toxic action but
is simply phenomenon of osmosis or
transmission of fluids through the
membranes. In order to prove this,
it is only necessary to weigh the an
NAL before and after the experiment.
A frog for example plunged in sea
water loses one-third its weight II on
ly the foot of the frog be introduced,
the blood of globules can be seen to
leave the vessels aud distribute them
selves under the skin. If an animal 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, some
times in fresh water, changing their
habitat in different periods of life or
of the year. 1t, the efore, In view of
the above becomes interesting to see
how NJ. Bert applies his discovery to
such apparent exceptions to the genar-
al rule. A fresh water salmon, for In
stance, plunged abruptly in sea water,
res;sts the effects longer than other
fresh water fishes, but he dies within
five or six hours. This shows accord
ing to NJ. Bert that the fish never pro-
ceed suddenly from fresh TO salt wa
ter but enter brackish water where the
tide ebbs aud flows, and lives there a
sufficient tine to habituate themselves
to the change. This accounts for the
frequent discovery of large numbers
of such migratory fish in the vicinity
of the mouths Of the rivers which they
ascend.
A fresh eel, plunged in salt water,
does not seem to be affected. But in
investigating the peculiarities of this
species M. Bert was led into wrong
conclusion which may be cited to show
how easy it is, often by pure accident
to reach an erroneous determination
in laboratory experimenting. After
having himself placed several fresh
water eels in salt water he found as al
ready stated that they remained alive
and unframed. Wishing to continue
the experiments, he directed his assls-
tant to introduce the fish and repor
results. To his surprise the eels then
persisfently died after three or four
hours sojourn in Salt water and 2long
search failed to discover the reason
why it was that; when M. Bert placed
them in the tanks they lived while
when the assistant did so, they perish
ed. Finally M Bert found that his
assistant doubtless on account of the
slipperyness of the eels lifted them
with a piece of cloth in his hand. The
cloth rubbed off little of the natural
slime of the animal, which protected
it from the salt water. Osmosis then
occurred in the denuded portion, and
the eel eventually died.
The converse experiment of insert
ing sea fish in fresh water produced
analogous results. The gills were the
seat of alterations, the same as those
noted in fresh water fish placed in salt
water. III. Bert also observed that the
life of the sea fish could be prolonged
by adding salt to the fresh water thus
adding further confirmation to his the
ory.-ScIentlfic American.