250
Fish Mortality in Tanks and Ponds in the Punjab
Accumulation of dead leaves, weeds, etc. On 17
April 1939, in the Student Farm tank at Lyallpur,
which received dead leaves from overhanging
trees, fish had come to the surface early in the
morning. The temperature of water was 80°
F. and its gaseous analysis gave results shown
in Table I.
TABLE I
Time
7 a. m.
10 a. m.
12 a. m.
5 P. m.
Tempe-
rature
80°F
82°F
85°F
85°F
Dissolved CO 2
c.c. per litre
Surface
0.077
1.072
1.197
2.253
Bottom
0.061
0.232
0.395
1.566
Free CO 2 c.c. per
litre
Surface
5.056
7.331
4.195
3.792
Bottom
7-078
7.331
5.309
4.803
As the day advanced, the conditions improved
and the fish returned to the bottom. Excess of
weeds in a tank or pond has often been found to
reduce the dissolved oxygen during the night, but
it increases during the day under the influence
of the sun. Addition of fresh water, swimming.
splashing of water and removal of excessive weeds
invariably improve the conditions in such tanks.
High temperature 1 . One of the tanks at the
Agricultural Farm at Lyallpur received on 12
June 1938, a supply of hot stagnant water that
had been standing in the supply drain after a
heavy rainfall on the previous day. The tempera-
ture of water rose from 82°F. to 92°F. All the
fish came to the surface gasping for air and 102
were picked up dead. These were Labeo rohita
(Hamilton), Labeo micropthalmus Day, and
Cirrhina mrigala (Hamilton). The water of the
tank was found to contain insufficient dissolved
oxygen and excess of CO 2 . Its contents were as
given in Table II.
TABLE II
Date and
time
12 June
10 pm.
13 June
7 a.m.
5 p. m. .
14 June
7 a. m. .
5 p. m. .
Dissolved CO 2
Surface
0129 to
0.201
0.048
0.776
0.353
5.298
Bottom
0.066 to
0.074
Nil
1.037
0.311
1.38
CO 2 c.c.p.l
Free
Surface
8.039
...
7.204
5.61
5.688
...
Bottom
7.836
...
4.929
5.435
5.308
...
Fixed
Surface
27.934
...
28.187
26.544
27.049
...
Bottom
27.176
...
29.072
25.783
26.544
...
1 The stagnant water, though it was not chemically
tested, did not appear to contain any such,impurity as
could have any deleterious effect on the fish.
The conditions improved with the addition of
fresh water on the 14 June.
Frost. A curious incident was observed in a
tank at Batala, where on 14 January 1942, at
6 a.m. hundreds of carp, namely Labeo rohita,
(Hamilton), Cirrhina mrigala (Hamilton) and
Catla catla (Hamilton), ranging in weight from 2
to 12 lb. were found floating upside down and un-
conscious near the banks as if frozen to death. As
soon as the sun came out the fish revived and re-
turned to deeper waters. Four were picked up
dead. The night between 13 and 14 January
1942 had been bitterly cold and frosty: the
temperature of water normally 56°F. had fallen
to 49°F. Consequently, the fish that had come
to the surface during the night, presumably be-
cause the surface water usually contains more
dissolved oxygen, were stupefied by the unusual
cold and frost. The gaseous contents of the water
of the tank on the day of incidence were not
known but the analysis of the water on the next
day, i.e. 15 January, showed that dissolved
oxygen on the surface was 1.974 c.c. per litre and
at the bottom 1.88 c.c. per litre while free CO 2
ranged from 3.792 c.c. to 10.112 c.c. per litre on
the surface and 3.539 to 11.378 c.c. per litre at
the bottom.
SUMMARY
The ease with which fish life in tanks and ponds
can be destroyed by inadvertence is illustrated
by the following instances :—
1. Soaking of wheat straw in a tank reduced the
dissolved oxygen to 0.041 c.c. per litre on the sur-
face and 0.137 c.c. per litre at the bottom, and
increased CO 2 to 13.651 c.c. per litre. The fish
came to surface gasping for air.
2. Dissolved oxygen was found to be absolutely
lacking in a tank in which a cart load of thrashed
wheat straw (toori) had fallen and had remained
for five hours.
3. Accumulation of dead leaves and excess of
weeds in a tank reduced the dissolved oxygen to
0.077 c.c. per litre and increased CO 2 to 7.078 c.c.
per litre. The fish came to the surface early in
the morning gasping for air, but condition im-
proved as the day advanced and fish returned to
the bottom.
4. Addition of warm stagnant water to a tank
killed 102 fish by sudden rise of temperature from
82°F. to 92°F., and consequent reduction of dis-
solved oxygen to 0.129 c.c. per litre and in-
crease of free CO 2 to 8.039 c.c. per litre.
5. Exposure to severe cold and frost made
hundreds of carp in a tank unconscious and killed
four of them. The fish were seen floating upside
down near the banks but revived when the sun
came out and returned to deeper waters.