3.3. Water chemistry
Mean values of water quality were calculated to
provide an overview of changes in the recirculatory
tank during the experimental period. Water recirculatory
system used in the experiment larval rearing of
C. chitala was found to be useful with respect to
levels of dissolved oxygen, free carbon dioxide and
maintaining water flow. The system also reduced
negative environmental impact and maintained stable
water quality conditions in the systems. No marked
variation in water quality parameter was observed in
experimental system treated with different diets except
boiled egg-yolk treatments where rapid breakdown of
feed caused fouling in the system. All the parameters
were under the tolerance limit of fish and they did not
exhibit any distress during the experiment. Dissolved
oxygen (DO) is the key factor in rearing of larvae
because larvae need optimum level of oxygen for
maintaining their physiological condition. In the
present study, mean dissolved oxygen level in the
recirculatory fish tank was 9.12 ±0.14 mg/L at
10.00 h. The water pH was 8.46±0.04 during rearing
period, a higher level whereas mean free Co2 was
0.36±0.07 ppm. In the daytime, fish consumed more
oxygen while their carbon dioxide excretion reduced
the pH range.