Stable isotope determination in wild and farmed gilthead sea bream (Sparus aurata) tissues from the western Mediterranean

Stable isotopes of carbon and nitrogen (δ13C and δ15N) have been determined in wild and farmed gilthead sea bream (Sparus aurata) samples of white and red muscle, liver, gills and gonads. First, δ13C and δ15N values were determined in samples with and without lipid removal to check the possible effect of lipid content on the stable isotope values of the different tissues studied. Differences were found for δ13C in all tissues studied apart from white muscle of wild fish, the tissue with the lowest lipid content. For δ15N values no differences were found in wild fish tissues. Liver from farmed fish showed lower δ15N value after lipid removing. Further conclusions were based on results obtained from lipid-free samples. δ13C of cultured fish tissues showed a mean depletion of 2.9 ± 0.4‰ compared to wild specimens, suggesting different sources of carbon in the diet, probably due to the feed used during sea-cage culture. Cultured gilthead sea bream tissues were significantly more enriched in nitrogen than wild specimens by an average of 1.5 ± 0.2‰ in white muscle, indicating a slight increase in the trophic level. Determination of stable isotope signatures of gilthead sea bream tissues allows clear discrimination between wild and cultured sea bream, and characterisation of differences in diet and feeding conditions in any tissue studied.