2018 Volume 65 Issue 1 Pages 1-7
Carbon and nitrogen stable isotope ratios (δ13C and δ15N, respectively) have been widely used to estimate food habits of animals, based on constant differences in isotope ratios between such animals and their diets, namely, trophic (diet–tissue) discrimination factors (TDF). However, recent studies have found the latter to vary more between different tissues or species than recognized previously. An aquarium experiment, in which ayu (Plecoglossus altivelis altivelis), a representative Japanese freshwater fishery resource, were cultivated with isotopically identical food (well-mixed commercial fish food), thereby obtaining TDF specific to muscle tissue, ovarian tissue and epidermal mucus, enabled estimation of the effect of lipid content on δ13C values. That in muscle tissue was 0.8‰–5.6‰ higher in lipid-eliminated samples than in untreated ones and was dependent on bulk C:N ratios, whereas the lipid content and its effect were constant in ovarian tissue. Lipid correction equations specific to muscle tissue of ayu were obtained by regressions on bulk C:N ratio, according to previously reported models. Lipid-free TDF in δ13C values differed between muscle tissue (2.4‰), ovarian tissue (1.9‰) and epidermal mucus (1.0‰). TDF in δ15N values also differed between muscle tissue (2.5‰), ovarian tissue (1.6‰) and epidermal mucus (1.5‰). The TDF and lipid correction equations for ayu demonstrated in this study enable accurate estimation of food habits and migration ecology of the species.
