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Field caging experiments were conducted on 0-group juvenile sea bass ( Dicentrarchus labrax ) and turbot ( Scophtalmus maximus ) in a polluted area. The fish were caged for 38 days in a northern French harbour (Boulogne sur Mer) at three locations with varying levels of contamination. Sediment from each location was analysed for PAHs, PCBs and metal contents, and their respective bioavailability. In the most heavily contaminated station, all the fish died during the two first weeks. At the two other stations, fish recovery was at least 75%. Growth and several health indices were individually measured on the tagged fish and metal bioaccumulation was measured in the fish gills. Juvenile sea bass physiological performance showed significantly higher growth rates, RNA:DNA ratio and Fulton's K condition index in the least contaminated station. The growth in weight and the condition index of the turbot caged in the less contaminated station were also higher. Similarly, for both species, lipid storage index based on the ratio of the quantity of triacylglycerols to sterols (TAG:ST), was significantly higher in the less contaminated station. This general decrease of growth and condition indices, associated with a metal accumulation in gills, reflected the adverse effects of contaminated sediment on the health of the fish. Species-specific responses to chemical contamination were recorded since a stronger relationship between physiological biomarkers and chemical contamination was observed in the sea bass. Therefore, this study supports the use of sea bass as model species and recommends measurements of physiological biomarkers for monitoring complex exposure.

International audience; The aim of the present study was to evaluate the effects of metal contamination on the biological responses of 0-group juvenile European flounder and to assess and compare the quality of four estuarine habitats located in the Eastern English Channel. Fish otolith growth and condition indices (RNA : DNA ratio, Fulton's K condition index) were measured and found to be significantly lower in individuals from the Seine estuary compared to those of the Canche, Authie and Somme estuaries. No obvious effects of hydrological condition or food availability on the flounder biological responses were observed. Sediments from the Seine showed the highest metal concentrations, bioavailable proportion and enrichment factors. Higher metal concentrations were observed in fish from the Seine compared to the other ones caught in less polluted estuaries. These results suggest that contaminants may have a negative impact on the early life history stage of flounder.

International audience; Juvenile turbot were exposed in laboratory conditions to a mixture of chemical contaminants associated with harbour and estuarine sediments for seven and 21 days. Several molecular biomarkers of exposure were then measured in fish liver: two biotransformation parameters [ethoxyresorufin-O-deethylase (EROD) and phase II glutathione S-transferase (GST) activities] and an antioxidant enzyme activity [catalase (CAT)]. Modifications at the histological level were analysed by the measurement of the number and size of melanomacrophage centres (MMCs) and disturbances to the immune function by the measurement of cytokine transforming growth factor-beta (TGF-β) and development of the thymus. The responses of these molecular and immunological biomarkers were correlated with metal and PAH concentrations measured in sediments and with the physiological performance of turbot analysed in a previous study on the same fish (growth rates, condition factor K, RNA:DNA ratio and lipid index). While no difference was found in thymus analysis, some molecular and immunological responses were observed in fish exposed to contaminated sediments. Weak relationships between molecular biomarkers' responses and PAH concentrations were recorded, while their responses were significantly correlated with some metals. MMC and aggregates were weakly related to chemical contaminants whereas some significant correlations were found between TGF-b1 responses and some metal concentrations. However, molecular and immunological biomarkers were weakly related to fish physiological damages since low responses were observed in the condition which led to the lowest growth and condition indices. These data suggest the complexity of cause-effect relationships between exposure to pollutants, metabolisms and health damages. Precautions should be considered in the use of molecular and immunological biomarkers alone in biomonitoring programs. Their complementary use with physiological biomarkers, such as fish growth and condition indices, could improve their utilisation.