The impact of environmental changes on the respiratory metabolism of the cichild fish Etroplus maculatus (Bloch) In the Veil Lake, a brackishwater lake on the southwest coast of India has been examined in detail. The routine metabolism of the fish has been checked with regard to temperature, salinity, hydrogen-ion-concentration and biocides on the rate of oxygen consumption.

The rate of oxygen consumption showed increase with increasing temperature and the fish could not tolerate temperatures higher than 41°C. At higher pH concentrations (8.8) there was increase in oxygen consumption while slight variations have no effect on the metabolism. The highest salinity tolerated by the fish was 16.65%o. The oxygen uptake was more in this medium and less at lower and higher salinities. The fish exhibited a maximum tolerance level of 0.04 mg/1 in the pesticide Nuvan. At the initial level of 0.005 mg/1 the fish exhibited the maximum oxygen uptake (0.5814 ml/ 1/gm body wt/hr), the rate at 0.01 mg/1 showed a slight decrease and the trend continued as the concentration increased. The fish could tolerate a concentration of upto 0.5 ml/1 of Dimecron. At 0.1 mg/1 the oxygen intake was 0.7647 ml/l/gm body weight/hr. Further increase in concentration of the pesticide resulted in a stress and gradual decrease in oxygen consumption. These indicate that the biocides have a depressive effect on the respiratory metabolism of the fish. The present study thus reveals that oxygen requirement of this fish in its estuarine habitat is quite characteristic and the demands depend on the environmental conditions.