Does the chronic chemical contamination of a European flounder population decrease its thermal tolerance

Abstract Juvenile flounders ( Platichthys flesus ) , collected in two estuaries with similar temperature regimes (the heavily polluted Seine and the moderately contaminated Vilaine), were submitted to a common garden experiment. After an acclimation period, both populations were challenged by a thermal stress (9–24 °C for 15 days, then maintenance at 24 °C for 19 days). The condition factor of the Vilaine fish increased in both conditions, while it decreased for the heated Seine flounders after 34 days. The expression of genes related to the energetic metabolism was measured in the liver. The expression levels for ATP-F0 and COII were significantly reduced for heated vs . standard fish from both estuaries, while a decrease of the 12S expression was detected only in heated vs . standard fish from the Seine estuary. Thus, it is suggested that highly contaminated fish from Seine could display a lower tolerance to thermal stress, compared to moderately contaminated fish from Vilaine.