ON CERTAIN INSTANCES OF FISH MORTALITY IN TANKS AND
PONDS IN THE PUNJAB
By. HAMID KHAN, M.Sc., LL.B. PH.D. (Cantab.), F.A.Sc., Game Warden, Punjab
(Received for publication on 30 March 1942)
SEVERAL instances of mortality of fish in rivers,
streams, tanks and ponds in India have been re-
corded before and after the monsoon rains. Some
of the main causes of such mortality are : putre-
faction of dead leaves, weeds and grass in stagnant
waters; excessively muddy water choking the gills
of the fish [Day, 1878; Chopra, 1926]; excessive
amount of CO 2 [Sewell, 1927]; deficiency of oxygen
caused by putrefaction of organic matter and pro-
bably also to the poisonous by-products of putre-
faction and sudden changes in water at or near
the height of the hot weather [Pruthi, 1932].
Excessive CO 2 and deficiency of oxygen ac-
cording to Pruthi have almost the same effect
on organisms, i.e. asphyxia, but the conditions
which bring about the increase in CO 2 and the
decrease in oxygen may be entirely different.
Sewell [1927] and Pruthi [1932] consider 8.3
c.c. per litre of CO 2 to be lethal for the fish. Powers
[1938] attributes the sudden mortality of fish
generally to abnormally high CO 2 tension of the
water and remarks that 'Death is not caused by
asphyxiation but by a derangement brought by
alternate compensation of the blood to higher and
then to lower CO 2 tension of the water. 'The
author [Khan, 1940] demonstrated by experi-
ments that carp-fingerlings confined in an
airtight container show signs of asphyxiation if
the dissolved oxygen available in water per fish
becomes reduced to 0.05 c.c. per litre and that
accumulation of free carbon dioxide up to 4.98
c.c. was not responsible for the asphyxiation of the
fingerlings.
During the study of physical and chemical en-
vironments of fish in tanks and ponds at Lyallpur
and Batala, where fish culture is in progress, some
interesting instances of fish mortality were ob-
served which will be of interest to pisciculturists
in rural areas, as they illustrate the ease with
which fish life in tanks and ponds can be destroyed
by inadvertence and demonstrate the need for
precaution if fish farming is to be a success.
METHODS
The determination of dissolved oxygen was
carried out by Winkler's method as given by
American Public Health Association [1936], and
of absorbed oxygen by Forchammer's process as
described by Stocks [1932]. Amount of CO 2
was determined by Seyler's method as given by
Kemmerer, Bovard and Boorman [1924].
Samples of water from the bottom of the tank
were collected in a wide-mouthed glass bottle of
one litre capacity, fitted with rubber cork, having
two glass tubes; one for the entry of the water and
the other for the escape of displaced air from the
bottle. To the second glass tube was attached
a 10 or 12 feet long rubber tubing fitted with a
clamp. The bottle, fitted in an iron frame, was
lowered into the tank and the rubber tubing, which
projected outside the surface of water, was kept
closed by tightening the clamp. As soon as the
bottle reached the bottom of the tank, the clamp
was loosened, the air from the bottle escaped
through the rubber tubing and was replaced by
water, which filled the bottle.
Soaking of wheat or wheat straw. (i) On 9 May
1939 soaking of wheat straw in the Student Farm
Tank at Lyallpur reduced the dissolved oxygen
and increased the CO 2 to such an extent that fish
came to the surface gasping for air and were saved
in time by removal of the straw and addition of
fresh water. Temperature of water was 83°F.
and its gaseous contents at 11-30 a.m. showed that
dissolved oxygen ranged from 0.041 c.c. per litre
at surface to 0.137 c.c. per litre at bottom, while
absorbed oxygen was 0.61 to 0.64 parts per
100,000, free CO 2 13.651 c.c. per litre to 12.893
c.c. per litre and fixed CO 2 , 31.347 c.c. per litre
to 32.864 c.c. per litre at surface and bottom res-
pectively. The water was, thus, poor in dissolved
oxygen, rich in organic matter and had plenty of
free CO 2 .
(ii) On 28 June 1939, a cart load of threshed
wheat straw (toori) fell in the Agricultural
Farm tank at Lyallpur and remained there for five
hours. Next morning all the fish had come to the
surface; eight were found dead and 105 were
immediately removed to another tank. Tempera-
ture of water was 90°F. and dissolved oxygen in
the surface water was entirely lacking, while at
the bottom of the tank it was 0.351 c.c. per litre.
On 1 July 1939, at 8 a.m. temperature being 85°F.,
the dissolved oxygen was found lacking both at
the surface and bottom, absorbed oxygen was
1.09 parts per 100,000, while free CO 2 ranged from
5.814 c.c. per litre at the bottom to 6.067 c.c.
per litre at the surface. As the conditions did not
improve, the tank had to be emptied, cleaned and
refilled with fresh water.
(iii) Soaking of wheat in gunny bags in the
Botanical Garden tank at Lyallpur, stocked with
larvicidal fish, produced similar effects as soaking
of wheat straw, and caused heavy mortality of the
fish.
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