Utility of Fishes as Bio-indicators for Tracing Metal Pollution in the Cochin Backwaters, Kerala, India

Trace metal (Fe, Ni, Zn, Cu, Pb, Cd and Cr) concentrations in water and tissues (flesh, gills and liver) of two fishes, Etroplus suratensis and Arius arius from the Cochin backwaters were investigated during February 2017 to January 2018. Trace metals were analysed using an Atomic Absorption Spectrophotometer (AAS). The omnivorous species, E. suratensis showed a higher concentration of trace metals in tissues than the carnivorous species, A. arius. Bioaccumulation of metals in fish tissues showed higher levels in the liver, which was followed by gill and flesh maybe due to the different physiological roles of these organs in fish metabolism. Bioaccumulation factors (B AF) of metals calculated for the species, E. suratensis follows an order Fe > Zn > Ni > Cu > Cr > Pb > Cd whereas that for the species, A. arius follows an another order Fe > Zn > Cr > Cu > Ni > Pb > Cd. Comparatively higher BAF values in organs of fishes indicate the increased concentration of the soluble metal in the medium in which the fishes inhabit. Metal selectivity index (MSI) and tissue selectivity index (TSI) are better tool for explaining bioaccumulation of trace metals in fishes. The results of the present study suggest the potential use of fishes, E. suratensis and A. arius as bioindicators for tracing metal pollution in the estuarine environment of Cochin.