13C and 15N analysis in muscle and liver of wild and reared young-of-the-year (YOY) Atlantic bluefin tuna

Stable isotope analysis (SIA) has become a useful tool in trophic ecology research, but experimental studies are essential for their correct application in field studies. Young-of-the-year (YOY) Atlantic bluefin tuna (ABFT) caught in the Mediterranean Spanish coast were reared on a common natural prey to determine prey-muscle and prey-liver discrimination factors. Significantly increased isotopic values were found in lipid-extracted tuna samples of muscle and liver versus bulk samples, while C:N values decreased following lipid extraction. Such isotopic differences were paralleled by differences in the discrimination factors estimated for δ13C (Δ13C) in muscle and liver, though Δ15N was apparently unaffected by lipid removal. Isotopic differences were observed between muscle and liver for wild ABFT, which was probably due to different turnover rates. The Δ13C estimates obtained from lipid-extracted samples of muscle and liver were 0.32 ± 0.04 and 0.39 ± 0.23, respectively. Δ15N values estimated from bulk samples were 1.46 ± 0.06 for muscle and 1.62 ± 0.22 for liver.

► Stable isotope analysis (SIA) proves useful in young tuna trophic biology studies.
► Removal of lipids results in depleted C:N, and enriched δ13C and δ15N values.
► Lipid extraction causes significantly increased Δ13C values but no change in Δ15N.
► The estimated discrimination factors for muscle are Δ13C = 0.32 and Δ15N = 1.46.
► The estimated discrimination factors for liver are Δ13C = 0.39 and Δ15N = 1.62.