Consequences of exposure to polyaromatic hydrocarbons (PAH), toxic components of crude oil, on fish has been widely documented due to their ecological and economical importance. However, although forming a valuable and consistent body of knowledge, use of these data in spill response is limited. Objective of the present study was thus to facilitate the translation of published data into information of operational value. For this, we investigated the dose‐response relationship between dispersant‐treated oil exposure and ecologically‐relevant consequences by combining laboratory and field experiments. Effects were examined over almost a year using juveniles of the slow growing, commercially important European sea bass (Dicentrarchus labrax). Moreover, a reliable interpretation of biomarkers response requires a complete knowledge of the factors likely to affect their response. Inter‐populational variability is of particular importance in environmental impact assessment since biomarkers' response from population collected in an impacted area are classically compared to those collected in a clean site. Our study revealed no effect of the exposure to dispersant‐treated oil on fish hypoxia tolerance and temperature susceptibility 1 and 11 months post‐exposure. Similarly, no effect of the exposure was observed on fish coping ability with environmental contingencies in the field, regardless of the dose tested. Thus, we are confident in suggesting that a 48‐h exposure to chemically treated oil do not affect the ability of sea bass to cope with mild environmental contingencies. Finally, investigation of interpopulation variability revealed large differences in both hypoxia tolerance and temperature susceptibility among the 2 populations tested, suggesting that this variability may blur the interpretation of populations comparisons as classically practiced in impact assessment.