Comparison of the stable carbon and nitrogen isotopic values of gill and white muscle tissue of fish

The potential use of stable carbon and nitrogen isotope ratios (δ13C, δ15N) of fish gills for studies on fish feeding ecology was evaluated by comparing the δ13C and δ15N of gill tissue with the more commonly used white muscle tissue. To account for the effect of lipid content on the δ13C signatures, a study-specific lipid correction model based on C:N ratios was developed and applied to the bulk δ13C data. For the majority of species in the study, we found no significant difference in δ13C values between gill and muscle tissue after correction, but several species showed a small (0.3-1.4‰) depletion of 13C in white muscle compared to gill tissue. The average species difference in δ15N between muscle and gill tissue ranged from − 0.2 to 1.6‰ for the different fish species with muscle tissue generally more enriched in 15N. The δ13C values of muscle and gill were strongly linearly correlated (R2 = 0.85) over a large isotopic range (13‰), suggesting that both tissues can be used to determine long-term feeding or migratory habits of fish. Muscle and gill tissue bulk δ15N values were also strongly positively correlated (R2 = 0.76) but with a small difference between muscle and gill tissue. This difference indicates that the bulk δ15N of the two tissue types may be influenced by different isotopic turnover rates or a different composition of amino acids.