Evaluating the suitability of fin clips as a tool for dietary biochemical analyses in pelagic teleosts

Muscle and liver tissues are widely used in trophic ecology studies of fish but often require lethal sampling, raising logistical, ethical, and conservation concerns. We investigated the use of pectoral fin clips as a non-lethal, minimally invasive alternative for studying the trophic ecology of southern bluefin tuna ( Thunnus maccoyii ), an endangered species of economic and ecological value. Muscle, liver, and fin clips were analysed for stable isotope composition (δ¹³C, δ¹⁵N, C:N), lipid content, and fatty acid profiles across their migratory range of southern Australia, accounting for variation by region and year. This approach assessed whether the trends in spatiotemporal variation in biochemical markers from muscle and liver were detectable with fin clips. We found significant regional and temporal variation in isotopic composition, lipid content, and fatty acid profile, with muscle tissue most effective at capturing these trends, while liver tissue showed more variability. Fin clips did not capture spatiotemporal variation in isotopes and lipid content as effectively as other tissues, limiting their value for detailed dietary or environmental analyses. However, they were useful for detecting variation in fatty acids, particularly polyunsaturated fatty acids EPA and DHA, important for human nutrition. Although fin clips may not fully capture spatiotemporal variation in isotopes and lipid content, they provide a less invasive option for robust fatty acid analysis, supporting nutritional monitoring in aquaculture and conservation of endangered pelagic teleosts. This study highlights the value of evaluating multiple biochemical approaches to assess the efficacy and limitations of different tissue types in trophic ecology.