Abstract: Parallel analysis of heavy metals (Pb, Cd, Hg, As, Zn and Fe) in muscles and guts of fishes, seawater and fish parasites were detected by atomic absorption Spectrophotometry. The bioaccumulation potential of heavy toxic metals was assessed in the Echinocephalus sp. and Ascaris sp. which is, reported as natural bioremediator of heavy metals in Liza vaigiensis from Karachi coast. Investigation suggests that infected fish contain low concentration of heavy metals in their muscle as compared to non - infected one. The high level of toxic metals in Echinocephalus sp. and Ascaris sp. within its host suggests that these nematode parasites are sensitive indicator of heavy metals in aquatic ecosystem showing sharing of more burden of environmental pollution of sea and also act as bioremediator of heavy metals in fish.