Biochemical and behavioral responses in gilthead seabream (Sparus aurata) to phenanthrene

Most toxicological studies with PAHs investigate their impact on aquatic organisms only at very specific levels of organization, either at molecular and cellular levels via biomarkers, or at higher integral endpoints such as reproduction and behavior. The link between both has received less attention in science. The aim of this multi-response study was to investigate the relationship between specific molecular processes (induction of biotransfon-nation enzymes and oxidative stress) and the behavioral performance of fish. We performed two concentration-effect studies with juvenile gilthead seabream (Sparus aurata), at which fish were exposed for 4 days to phenanthrene (PHE) (0.11 to 0.56 mu M). Groups of five fish per aquarium were recorded for changes in the patterns of their movement and social interactions. Biomarkers analyzed were ethoxyresoru fin-O-deethlylase (EROD), total glutathione-S-transferase (GST), phenanthrene-type metabolites in bile, lipid peroxidation (LP), superoxide dismutase (SOD) and catalase (CAT). The physiological status of the fish was determined by the liver somatic index. In general, PHE changed the overall behavioral performance of fish, all behavior activities were affected in a dose-response way. The incidence of lethargic fish was strongly increased (Lip to 39%). as the fish activities were reduced. The changes in the individual swimming activity had influenced negatively the social behavior of fish groups, i.e. the more fish in the group were lethargic, the less the social interactions were marked. The biornarkers responded to PHE differently, with an increase of EROD activity at low exposures (72.25 pmol min(-1) prot(-1)), but an inhibition at high concentrations (42.60 pmol min(-1) prot(-1)). For GST, we observed the reverse pattern. Together with the strong increase of PHE-type metabolites in bile, we conclude that both biotransfort nation enzymes are involved in the metabolism of PHE in liver. We found indications for oxidative stress already at low PHE concentrations, as LP levels were increased in the liver. However, higher exposures provoked less pronounced levels, but elevated activities of the antioxidants CAT and SOD (up to 37% and 17%, respectively). We conclude that especially the enzymatic activations at high-PHE exposures might have required additional energetic costs for the chemical detoxication that lead to the marked changes in the fish behaviors, i.e. demonstrating a "trade-off'' between detoxication processes via the biliary-hepatic system and the fish activity. Thus, the strong increases in lethargy might be the consequence of higher energetic demands for the PHE detoxication. This illustrates how an integrated use of biomarkers can contribute to our understanding of the impact of PAHs at increasing levels of biological complexity. (c) 2007 Elsevier B.V. All rights reserved.