Abstract:
Use of some fish parasites as bioindicators of heavy metal pollution has been demonstrated as a promising approach because of their capacity to bioconcentrate such elements. This study evaluated the effects of a cestode parasite, Ligula intestinalis, on the accumulation of lead (Pb), cadmium (Cd), chromium (Cr) and copper (Cu) in the cyprinid fish, Rastreneobola argentea, in Lake Victoria, Kenya. This L. intestinalis/R. argentea model also was assessed as a bioindicator system for heavy metal contamination in the lake. Samples of 125 fish, 63 parasites, water and sediments were collected at four sites in the Kenya portion of the Lake Victoria basin characterized by variable heavy metal concentrations, for ICP-OES element analysis. The concentration of all four heavy metals in the fish and parasite samples exhibited site-specific variations relative to the metal concentrations in the water. The Pb, Cr and Cd concentrations in the L. intestinalis were higher than in the fish samples by a factor 11, 18 and 14 respectively, whereas the Cu concentration in L. intestinalis was increased by a factor of 2.5, relative to the Cu concentration in fish. The Pb, Cd and Cr concentrations in the parasite body increased, relative to their concentrations in fish samples, suggesting in the bioaccumulation of these metals by the parasite. The Cu concentration in the fish parasite decreased, relative to increased Cu levels in the fish. This finding was interpreted as being a competition for these elements between the parasite and its fish host. Moreover, the increased Cd and Cr levels in the fish were significantly influenced by the increased abundance of the parasites in the abdominal cavity of the fish samples. Based on the results of this study, the L. intestinalis/R. argentea system is proposed as a promising bioindicator model for evaluating environmental Pb, Cd and Cr concentrations where these species occur.