Abstract
We sampled and analyzed European flounder (Platichthys flesus) from two highly contaminated estuaries (Seine and Loire, France) and one moderately contaminated estuary (reference site: Ster, France). Significant and convergent modifications of the allelic frequencies for the loci phosphoglucomutase (PGM), glucose phosphate isomerase 2 (GPIβ2), mannose phosphate isomerase (MPI), and aspartate aminotransferase (AATβ2) were evident for fish in the contaminated sites versus fish from the reference site. Backβcalculation from otoliths showed that the average growth rate of fish between the first and the second winter was greater at the reference site (β150 mm/year) than at the contaminated sites (β100 mm/year). Flounder from the reference site also had a higher condition factor (somatic wt/(fish length)^3^) compared to fish from the two contaminated sites. However, the observed pattern of growth rate and condition factor might be biased by particular environmental conditions other than contaminants and must be confirmed by more extensive study. Flow cytometry analysis of fish blood revealed a significant difference in the frequency of abnormal profiles for fish from the Seine (20%) versus from the Ster (3%). We interpret this result as a marked genotoxic effect of contaminants on fish in the Seine system. Some genotypes, such as PGM 85/85, appeared to be linked to the measured components of fitness, particularly to DNA integrity. Thus, these genotypes might be considered to be more tolerant to pollutants. The frequency of the PGM 85 allele was clearly elevated in flounder from the more contaminated sites, compared to flounder from the reference site.