Biomagnification of organochlorine compounds (pesticides and polychlorinated biphenyls) through the marine aquaculture food chain is investigated. From first-feeding, specimens of sea bass were exposed to commercial fish feed (that contained DDTs and PCBs residues) for ca. 24 months, and selected tissues (white and red muscle, liver, and visceral fat) were analyzed after 6 and 24 months of diet exposure. Data obtained showed that experimental fish tissues presented a similar contamination pattern to that of fish feed, and biomagnification processes of these compounds were proved. Additionally, commercial sea bass cultured in farms from the western Mediterranean were analyzed, their organochlorine concentrations being significantly lower than those of the 24 month old experimental fish. Thus, the exposition of human population to OCs through consumption of cultured fish would be lower than expected from experimental biomagnification studies, although red muscle presented similar OC levels in both cases, which were much higher than those of white muscle. Although levels of organochlorine compounds were found to be low, the persistence, ubiquity, and toxicity of these compounds, together with their presence in fish feed, make it necessary to monitor OC residues in the routine quality assurance programs of aquaculture activities, as this food chain is a source of these toxic compounds for human consumers. The development of sensitive analytical methodology based on GC-MS/MS has allowed for the reaching of low detection limits required to carry out the present study.