Dispersants transfer oil from the water surface into the water column and consequently modify hydrocarbons petroleum fish uptake. It appears that toxicity will depend on whether oil dispersion increases or decreases the exposure of aquatic species to the toxic components of oil. Lethal bioassays were conducted on Liza aurata. During 48 h, fish were exposed under several pathways of oil contamination: water soluble fraction of oil (WSF), a chemically dispersed crude oil and a mechanically dispersed crude oil. In addition, a control condition with dispersant was evaluated. Hydrocarbons concentrations were determined along the exposure period (on their soluble and particular fraction). Following this period, a 14 days recovery period was conducted. Because understanding changes in fish immune system is relevant for evaluating the health of the aquatic environment, our study deals with modification of its response by recognised biomarkers such as the haemolytic activity of alternative complement pathway (ACH50). In addition, we studied gill surface and hepatic morphological histology to better understand the innate immunity alteration. Furthermore, physiological parameters including condition factor and liver somatic index, biotransformation enzymes such as 7-ethoxyresorufin-O-deethylase (EROD) and glutathione-S-transferase, antioxidant enzymes including glutathione peroxidase and total glutathione (GSH) content and lipoperoxidation (as TBARS) were measured in these conditions. These responses were correlated to the exposure level by bioaccumulation measurements before and after the decontamination period.