PHYSIOLOGICAL STRESS RESPONSES AS BIOMARKERS OF SENSITIVITY IN ESOMUS DANRICUS EXPOSED TO COPPERS.S.VUTUKURU, JUVERIA, V. IIIMABINDU AND Y. ANJANEYULU
Copper ions are quite toxic to fish when environmental concentrations- are increased often resulting in physiological, histological (tissue), biochemical and enzymatic alterations in living organisms, particularly fish. The occurrence of these alterations has a great potential to serve as biomarkers. Esomus danricus, which forms an important link in the aquatic food chain, was chosen as a model in the present study owing to its easy availability and maintenance, small size, easy to perform bioassays with little space and also due to lack of toxicological data for this species. Physiological responses (metabolic rate and ventilation frequency) of this fish were critically examined so that they can be employed as potential biomarkers for the rapid assessment of copper toxicity in freshwaters. Fish were exposed to different concentrations of copper sulphate and the 96h LC was determined to be 5.5 mg/I.. Later, fish groups were separately exposed to lethal (5.5 mg/L) and sub lethal concentrations (0.5 mg/L) of copper sulphate over a period of 96h to examine the subtle effects caused at physiological level. Experimental data showed that the lethal exposures of copper (5.5 mg/L) induced significant decrease in the metabolic rate (P<0.0u1) of the fish from that of control at the end of 24, 48, 72 and 96h exposure periods while in sub lethal exposure (0.5 mg/L) this decrease is significant at the end of 72 and 96h. Significant increase in the ventilation frequency of fish exposed to 5.5 and 0.5 mg/ L was also observed. However, this decreased as the concentration of the metal increased suggesting increased toxicity of the metal as well as the susceptibility of the fish. The metal proved to be a potential respiratory inhibitor.
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