Incremental analysis of vertebral centra can reconstruct the stable isotope chronology of teleost fishes

Isotope analysis has high potential for understanding fish ecology and food-web structure in aquatic ecosystems. The utility of isotope analysis will be greatly improved if we can reconstruct the chronology of several isotopes at multiple growth stages of individual fish. However, no practical methods exist for reconstructing the chronology of light-element isotopes (e.g. δ¹³C, δ¹⁵N, δ³⁴S, and Δ¹⁴C) in teleost fishes. Here, we present and test a new analytical approach for reconstructing the isotopic ratios of light isotopes at multiple life-stages in teleost fishes. We sampled an anadromous salmon species, masu salmon Oncorhynchus masou (n = 3), along with water from its natal stream and from the ocean. We subdivided the vertebral centra of the salmon equally into 10 sections and extracted bone collagen from each sample. We then measured the stable sulphur isotope ratios of each vertebral section and compared them with δ³⁴S values of the river water and sea water. We also measured the ⁸⁷Sr/⁸⁶Sr ratios of otoliths as a reference indicator of salmon migration between fresh water and the ocean. In all samples, the bone section closest to the centre of the centrum had the lowest δ³⁴S values, which were similar to those of fresh water. The δ³⁴S values gradually increased from the centre to marginal sections, finally reaching constant values similar to those of seawater. The ⁸⁷Sr/⁸⁶Sr ratios of sagittal otolith sections had significant inter-individual differences and were consistent with the patterns of variation of the δ³⁴S values of the vertebral sections. Our results show that the vertebral centra of teleost fishes record isotopic information from juvenile to adult life stages. We suggest that our method can provide reproducible isotopic chronology, even in teleost fishes smaller than 50 cm. This method can be used in isoscape studies and in studies of the ecology of marine teleost fishes.