Reclamation of wastewater for polyculture of freshwater fish: Bioaccumulation of trace metals in fish

To investigate the bioaccumulation of trace metals (Zn, Cu, Cd, Cr, Pb, Ni) in the polycultured fish, a series of eight ponds (Au Tau pond system) were constructed at Au Tau Fisheries Office, Hong Kong Agriculture and Fisheries Department. Polluted river water was pre-treated in the first four ponds by providing sedimentation (S1, S2) and aeration (A1, A2), the effluent from A2 was introduced into the remaining four ponds (C1-C4) for fish culture. Fries of six species of freshwater fish including silver carp, big head, grass carp, tilapia, common carp and black bass were stocked in ponds. Bimonthly sampling of fish enabled to determine trace metal concentrations. The distribution of trace metals in different components of the fish pond ecosystem was also determined.