Effect of Mercury and Cadmium on the Oxygen Consumption and Gill Histology of Catla catla (Ham. 1822)

Mercury and cadmium are among the major heavy metal pollutants, contaminating aquatic ecosystems. These heavy metals were investigated in the present study for sub lethal toxicity on freshwater fish, Catla catla. The acute toxicity tests were conducted by static renewal bioassay method and 96 h LC50 value of mercury and cadmium to C. catla seed were found to be 0.0835 and 0.4225 mg L−1, respectively. For sub lethal studies 1, 3, 6, 12 and 24 % of the 96 h LC50 value were selected and significant decrease in oxygen consumption up to a maximum of 82.9 % for mercury and 79.8 % for cadmium as compared to control were observed. The gills of fish exposed to sub lethal concentration of the metals showed histological alterations including oedema, hemorrhage, hyperplasia, hypertrophy, necrosis, curling and fusion. Both, oxygen consumption and histopathological changes were observed to be dose and duration dependent. Present study also indicates higher toxicity of mercury as compared to cadmium on C. catla.