The use of fish metabolic, pathological and parasitological indices in pollution monitoring - 1. North Sea

An integrated biological effect monitoring concept has been tested in floun der (Platichthys flesus L.) from four locations with different anthropogeni c impact in the German Eight. During 3 years of sampling, biomarkers at all levels of biological organisation from the molecular to the ecosystem leve l were applied and tested on 742 individual fish of body lengths between 18 and 25 cm. At the ecosystem level, the fish were taken as a habitat for th e parasite assemblage. The hypothesis was that changes in the environment m ight lead to changes in the species diversity of parasites and in the infec tion intensity of single species, as well as between heteroxenic and monoxe nic parasite species (H/M ratio). At the molecular level, activity of the C YP1A-dependent monooxygenase ethoxyresorufin O-deethylase (EROD) was used a s a biomarker of exposure. At the subcellular level, the integrity of lysos omal membranes in hepatocytes was taken as an indicator of non-specific acu te and chronic toxic effects. Both biomarkers are recommended by the ICES A dvisory Committee on the Marine Environment for the application in biologic al effects monitoring programmes. In addition, neutral lipid content in the liver was used as a marker for pathologically induced fat accumulation. In the same individual fish, a new method for the measurement of macrophage a ggregate activity in the liver was tested for its application and reliabili ty in reflecting immunosuppression. Tests were accompanied by chemical anal ysis of standard organochlorine and heavy metal residues in flounder tissue , A total of 33 parasite species were found. As an indicator species, the m ean abundance of Trichodina sp. reflected best the pollution gradient obser ved with highest infection intensity at the most polluted location. Species diversity was significantly higher in fish caught near the reference site and significantly lower in fish from the polluted Elbe estuary. The use of the heteroxenous/monoxenous species ratio as a marker was not useful at the locations investigated because of the dominance of heteroxenous species at all habitats. Since EROD activity and macrophage aggregate activity were d ependent on sex and maturity of female flounder, only male fish were taken into consideration for the integrated evaluation of data. All biochemical a nd histochemical tests were able to reflect accurately the site-specific di fferences, as well as an observed pollution event at the end of 1995 as det ermined by chemical analyses. The correlation analysis revealed a connectio n not only between the single parasitological and biochemical parameters bu t also within these groups. The non-specific immune response and TrichodinL 1 infection intensity were correlated with all other parameters, leading to the assumption that these may serve as links between the lowest and the hi ghest levels of biological organisation. The simultaneous use of metabolic and parasitological results facilitated the interpretation of the observed variations of the data and the distinction between natural variation and po llution-mediated effects.