Stable isotope turnover rates and fractionation in captive California yellowtail (Seriola dorsalis): insights for application to field studies.

Stable isotope analysis (SIA) measurements from long-term captivity studies provide required parameters for interpretation of consumer SIA data. We raised young-of-the-year (14-19 cm) California yellowtail (Seriola dorsalis) on a low δN and δC diet (pellet aquaculture feed) for 525 days, then switched to a high δN and δC diet (mackerel and squid) for 753 days. Yellowtail muscle was sequentially sampled from each individual after the diet switch (0 to 753 days) and analyzed for δN and δC, allowing for calculation of diet-tissue discrimination factors (DTDFs) from two isotopically different diets (low δN and δC: pellets; high δN and δC: fish/squid) and turnover rates of N and C. DTDFs were diet dependent: ΔN = 5.1‰, ΔC = 3.6‰ for pellets and ΔN = 2.6‰, ΔC = 1.3‰ for fish/squid. Half-life estimates from N and C turnover rates for pooled yellowtail were 181 days and 341 days, respectively, but varied considerably by individual (N: 99-239 d; C: 158-899 d). Quantifying DTDFs supports isotopic approaches to field data that assume isotopic steady-state conditions (e.g., mixing models for diet reconstruction). Characterizing and quantifying turnover rates allow for estimates of diet/habitat shifts and "isotopic clock" approaches, and observed inter-individual variability suggests the need for large datasets in field studies. We provide diet-dependent DTDFs and growth effects on turnover rates, and associated error around these parameters, for application to field-collected SIA data from other large teleosts.