Comparisons of heavy metal concentration of grass carp (Ctenopharyngodon idella Cuv. et Val.) in a shallow eutrophic lake and a fish pond (possible effects of food contamination).

Nickel, Cu, Zn, Cd, Pb and Hg concentrations were determined in gills, liver, kidney, muscle and gut of grass carp (Ctenopharyngodon idella Cuv. et Val.) collected from Lake Balaton (Hungary) and from a fish pond of a fish farm nearby. The body weight normalised heavy metal concentrations in different organs/tissues were compared and ordered for both Lake Balaton and the fish farm. Metal concentrations, in most cases were highest in kidney or in liver, and lowest in muscle or in gut. Nickel concentration was lower in liver, muscle and gills of fish from Lake Balaton. We suppose that an earlier sewage water load resulted in the higher Ni levels in grass carp from the fish pond. Mercury concentration was also lower in the gut of grass carp from Lake Balaton, but the other organs showed higher concentrations at this location. Our results suggest that the accumulation mechanism of Hg may be different from other metals in non-predatory fish species. Mercury uptake from food may be dominant for all fish species, but 'biomagnification' becomes obvious only in the case of predatory species.