Comparison of stable isotope composition and inorganic and organic contaminant levels in wild and farmed bluefin tuna, Thunnus thynnus, in the Mediterranean Sea.

Stable isotope composition (delta(13)C and delta(15)N) and persistent pollutants, including heavy metals (Hg, Cd, Pb, As, Cu, Zn) and organochlorine compounds (PCBs, HCB and p,p'-DDE), were measured in muscle and liver tissues of wild and farmed bluefin tuna to investigate the changes occurring during the farming period and to assess the quality, in terms of contaminants, of the final product. At the end of farming, the food supplied was clearly integrated into the tuna tissues as derived from stable isotope signatures, and, contrarily to the literature findings obtained for other species, farmed tuna showed slight variations in persistent elements and chemical compounds in comparison with wild fish. The low tissue turnover of long-lived adult tuna together with the short farming period appeared to act to preserve the initial low contamination levels in the absence of new, elevated contamination sources (feed and environment), determining an acceptable quality of the final aquaculture product.