Concentrations of organochlorine substances in relation to fish size and trophic position: A study on perch (Perca fluviatilis L.)

The aim of this study was to evaluate, the importance of; trophic position as a determinant of the concentrations of organochlorine substances (OCS) i n fish. Perch (Perca fluvatilis)was selected since the species increases in trophic level over the course of its lifetime. The trophic position was ch aracterized by stable isotope analysis of nitrogen and gut content. Perch ( 130 individuals) of different lengths and of both sexes were analyzed for p olychlorinated biphenyls and chlorinated pesticides. There were no pronounc ed differences in the OCS concentrations between the perch sexes. Perch up to a length of 20 cm did not show any increase in OCS concentrations with i ncreased length, despite a pronounced increase in trophic position. Thus, t he trophic position cannot explain the observed concentrations of OCS in sm aller perch. In perch >20 cm, the levels of all analytes increased with len gth or trophic position. The magnitude of the concentration increase was po sitively correlated with the lipophilicity of the substance. The increase o f OCS concentrations in the large perch is explained by physiological chang es leading to slower OCS clearance or by such changes in combination with h igher OCS intake due to higher trophic position.