Influence of different temperature-salinity combinations on the oxygen consumption in the fresh water fishEtroplus maculatus (Teleostei)

Abstract

1. Oxygen consumption ofEtroplus maculatus was measured immediately upon transfer into different temperature-salinity combinations. Four salinities (fresh water, 9.7‰, 19.4‰ and 32.4‰) and three temperatures (25°, 30° and 35° C) have been used in the combinations indicated. 2. The effects of temperature-salinity combinations on oxygen consumption were analysed on a size basis. In larger fish, temperature increase augments oxygen consumption in all test salinities. These changes are a function of the salinity, and, in addition, are size dependent. In the higher salinity levels, sudden temperature increase tends to result in relatively lower rates of oxygen consumption (compared to the rates obtained at 25° C) in the smaller fish (depression), but in relatively higher rates in the larger ones (elevation). 3. Similarly, the effects of salinity on the oxygen consumption were modified by temperature. At higher temperatures, increased salinity depressed the oxygen consumption of the smaller fish and elevated that of the larger ones. 4. Smaller individuals exhibited the highest O2-consumption in combinations of high temperatures and low salinities, while the larger ones exhibited maximum O2-consumption in combinations of high temperatures and high salinities. 5. The possibility of the existence of differences in the osmoregulatory abilities between the smaller and larger individuals ofEtroplus maculatus is suggested. But no conclusive evidence is available at present either in support of or against this hypothesis.