Responses of fish populations to chemical stress in estuaries : molecular, biochemical and immunotoxicologic approach
Coastal and estuarine environments are mainly impacted by anthropogenic activities that lead to several stress (chemical and/or thermal stress, hypoxia…). Presence of complex mixtures of contaminants could create serious damages in aquatic ecosystems and also in human populations.During this work, two studies were carried out in France and Québec, on two species: the European flounder (Platichthys flesus) and the Atlantic tomcod (Microgadus tomcod), these fishes being considered as sentinel species of the water estuarine quality. A multi-parameter approach was conducted considering the fish responses to the chemical stress, from molecular to individual levels (gene expression, detoxification process, functioning of the immune system, energetic metabolism and condition index). The main objective of this study was to identify the more pertinent biomarkers to evaluate the estuarine water quality.Firstly, the flounder responses were studied in controlled conditions after 29 days of contamination with environmentally relevant concentrations of PAHs and PCBs in food, followed by a 14 days recovery period. The contaminated diet impacted the immune system and showed an increase of the detoxification process and of the DNA damages. Up-regulation of the complement C3 and TNF-receptor gene expressions could be explain by an inflammatory response in liver. The lysozyme level was also impacted and appeared to be the more sensitive immune parameter to the chemical stress. This study underlined a significant correlation between the Cytochrome P450 1A1 expression level and the DNA damage.Secondly, the previous markers were explored on the flounder and the tomcod, considering the fish population responses to contaminants in the field. These two studies underlined the complexity of the immune responses to contamination, some functions being inhibited (capacity of phagocytosis) whereas others being enhanced (expression of C3 and TNF-R, proliferation of lymphocytes). Moreover, this multiparameter approach confirmed the pertinence of several markers in experimental conditions as in the field. This study carried out on flounder and tomcod populations showed differential responses of populations in contaminated vs in pristine sites (particularly considering: energetic metabolism, detoxification process, immune response and condition index), linked to fish aging (0+ vs 1+ cohorts).