Oxygen utilization in Cirrhinus mrigala and Labeo rohita under normoxic and hypoxic conditions

Abstract

Oxygen consumption, ammonia excretion and ammonia quotient in Indian major
carps, Cirrhinus mrigala and Labeo rohita were tested in freshwater at 30 +10C
under different oxygen concentrations using Fry's respirometer. The oxygen
consumption was 295.12 and 92.68 ml/kg/hr under normoxia and hypoxia respectively
in C. mrigala. In L. rohita the mean oxygen consumption was 297.16
and 104.40 ml/kg/hr under normoxia and hypoxia respectively. Ammonia excretion
was 11.41 ml/kg/hr under normoxia and during hypoxia it increased significantly
(P<0.05) to 18.24 ml/kg/hr in C. mrigala. In L. rohita ammonia excretion
increased from 12.15 to 18.45 ml/kg/hr. The increased ammonia production
under hypoxia is an advantage in maintaining acid-base balance and also in
conserving sodium ions (Na+) during anaerobic metabolism of fish. The average
ammonia quotient values under hypoxic conditions are 0.2207 and 0.2107 in C.
mrigala and L. rohita respectively, which are below the maximum aerobic value
(0.335). In both the species, the level of oxygen uptake paralel with the fall in
environmental PO2 (partial pressure of oxygen) suggesting that both C. mrigala
and L. rohita are 'oxyconformers'.