Synergistic Effects of Metals (Cobalt, Chromium and Lead) in Binary and Tertiary Mixture Forms on Catla catla, Cirrhina mrigala and Labeo rohita

Acute toxicity tests, in terms of 96 h LC50 and lethal concentrations of individual metals (Co, Cr and Pb) and their mixtures were conducted under controlled-laboratory conditions to evaluate the sensitivity of major carps viz. Catla catla, Cirrhina mrigala and Labeo rohita. All tests were performed under constant water temperature (30 degrees C), pH (7.50) and total hardness (225mgL(-1)). Fish fingerlings (110-day age) were first acclimatized to laboratory conditions and then shifted to glass aquaria for toxicity experiments. During the whole acute toxicity trails, fish mortality was observed at 8 h intervals, while physico-chmical variables of water viz, carbon dioxide, dissolved oxygen, pH, potassium, sodium, temperature, total hardness and total ammonia were checked at 12 h intervals. Fish mortality data were analyzed through probit analysis method at 95% confidence interval to compute 96 h LC50 and lethal concentrations of individual metals and their mixture for each fish species. Among the major carps, Catla catla showed significantly (p<0.05) higher sensitivity to all metals with the mean 96 h LC50 and lethal concentrations of 40.16 +/- 22.72 and 71.33 +/- 39.98mgL(-1), respectively, followed by that of Labeo rohita and Cirrhina mrigala. Among all treatments, Co+Cr+Pb mixture appeared significantly most toxic to the fish than that of individual metals and their binary mixtures. Results suggested that metals (Co, Cr and Pb) in a mixture form showed synergistic effects on the fish. However, there existed 2x synergistic effects for Co+Cr, Co+Pb and Co+Cr+Pb while that for Cr+Pb mixture was 3x.