Muscle and scale isotopic offset of three fish species in the Mediterranean Sea: Dentex dentex , Argyrosomus regius and Xyrichtys novacula

Diet information of organisms was traditionally acquired by the use of lethal techniques (gut content or muscle delta(13)C and delta(15)N isotopic ratios). An increase in the number of isotopic ratio studies and the vulnerability of some species have led to increased use of non-lethal methodologies for conservation purposes. In the present work we have compared the delta(13)C and delta(15)N isotopic signals of muscle and scales of three different fish species in order to test fish-scale sampling as a non-lethal technique in fish trophodynamics. A positive correlation was found between muscle and scales in Argyrosomus regius and Xyrichtys novacula, while Dentex dentex showed no correlation due to the small length range of this species. The isotopic offset (Delta(13)C and Delta(15)N) between muscle and scales was significantly different among species (analysis of variance (ANOVA), p < 0.001) with Tukey's post-hoc HSD indicating a tissue offset difference (p < 0.001) for both stable isotopes in all species, except for Delta(13)C between A. regius and X. novacula and for Delta(15)N between D. dentex and X. novacula (p > 0.05). Mean delta(13)C and delta(15)N values between species showed significant differences (paired t-test, p < 0.01) between muscle and scale with an enrichment for delta(13)C and a depletion for delta(15)N. Spatial differences were found in the Delta(13)C of X. novacula between the studied locations, while no differences were found for Delta(15)N, indicating that non-geographical differences should be considered in the application of scales instead of muscle for (15)N, while for (13)C differences in the geographical isotopic offset should be considered.