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Oxygen Requirements of Indian Carp
(c) Oxygen requirements of four carp fingerlings.—(i) The oxygen consumed
by four carp fingerlings in three hours (Table III) ranged from 1.501 c.c.
to 3.3903 c.c. per litre, at the rate of 0.375 c.c. to 0.8476 c.c. per litre per
fish. The lowest value of dissolved oxygen in the container at the end of
the experiment was 0.373 c.c. per litre, i.e. 0.093 c.c. per litre per fish, which
is above the lethal limit.
(ii) The oxygen consumed by four carp fingerlings in one hour (Table III)
ranged from 1.047 to 2.111 c.c. per litre, i.e. 0.262 to 0.528 c.c. per litre
per fish.
(d) Oxygen requirement of one carp fingerling.—One carp fingerling
in three hours consumed from 0.382 to 1.886 c.c. per litre (Table IV).
In one hour it was found to consume 0.243 to 0.678 c.c. per litre.
The rate of oxygen consumption by carp fingerlings in all the cases ranged
from 0.202 to 0.678 c.c. per litre per fish in one hour.
CARBON DIOXIDE (TABLE V)
In the case of one carp fingerling free carbon dioxide did not show any
appreciable increase at the end of the experiment. When four fingerlings were
confined in the container free carbon dioxide showed an increase ranging from
0.253 to 1.348 c.c. per litre. There was appreciable increase when eight to
twelve carp fingerlings were put in the medium. Where water was definitely
neutral at the commencement of the experiment, the free carbon dioxide
at the end of the experiment with twelve fingerlings was found to range from
3.2232 to 4.98 c.c. per litre. The pH value invariably showed a definite
fall from 8.2 to 7.2 or 7.4.
In order to investigate whether accumulation of free carbon dioxide was in
any way responsible for asphyxiation of the fingerlings, control experiments
were run where the glass container with the carp fingerlings was not closed
and in it same number of fingerlings were put as in the closed containers. When
the fingerlings in the closed containers turned upside down, oxygen contents
and carbon dioxide of the open container were also determined. It was found
that carbon dioxide in the open container ranged from 3.085 to
4.74 c.c. per litre, which was not in any way less than that found in closed
container. Oxygen concentration had also been reduced (Table VI). The
fingerlings in open container, however, did not show any sign of asphyxiation
as the oxygen concentration was not so much reduced as to reach the lethal
limit The oxygen concentration in the control, for instance, in the case of
eight fingerlings was 8.385 c.c. per litre, but at the end of the experiment it
was estimated to be 0.7105 c.c. per litre, i.e. 0.0888 .c. per litre per fish, which
is above the lethal limit. In the case of twelve fingerlings it was reduced
from 6.527 to 0.6325 c.c. per litre, i.e. 0.0527 c.c. per litre per fish,
which is just above the lethal limit. It was, however, possible to keep the
fingerlings in the open jars for a long time by stirring the water by a glass rod.
The oxygen concentration by stirring increased in one instance from 0.5401
to 4.3993 c.c. per litre though free carbon dioxide did not decrease
appreciably. It is evident, therefore, that accumulation of free carbon
dioxide was not responsible for the asphyxiation of the fingerlings, but it was
due to lack of oxygen in the medium.