Species-specific trophic enrichment factor of stable nitrogen and carbon isotopes in fish otolith organic matter

Abstract

Context Although stable carbon (δ13C) and nitrogen (δ15N) isotopes are widely used to study feeding ecology, the use of these isotopes in otolith organic matter to assess the diet of fishes is rarely investigated. Aim This study evaluated the relationship of δ13C and δ15N values among muscle, otolith organic matter and diet. The samples were analysed using an elemental analyzer connected to isotope-ratio mass spectrometry. Key results The δ15N values were highest in muscle followed by otoliths, diet and plankton, although no significant difference in δ15N values was found between the otolith and diet for most of the samples. The fish collected from water reservoirs showed similar δ13C values between otolith and muscle, both of which were higher than the isotopic values of the fish diet. However, the farmed fishes showed small but significant difference in the δ13C values between muscle and otolith, which reflects diet change or commercial diet containing a mixture of different food items. Conclusion Otolith δ15N value can provide information about fish diet and the otolith δ13C value can act as a good proxy of muscle δ13C composition in fish species. Implications Otolith δ15N and δ13C values can faithfully reflect the trophic position and feeding behaviours of fish.