Variability in δ13C and δ15N trophic discrimination factors for teleost fishes: a meta-analysis of temperature and dietary effects

Stable isotope analysis (SIA) is widely used to assess animal diet and movements, requiring accurate estimates of trophic discrimination factors (TDFs). Since TDFs are only available for a limited number of species, SIA applications typically rely on universal across-taxa averages, disregarding potential sources of variability such as phylogeny, temperature, and diet. We compiled 20 published articles reporting experimental TDF measurements for carbon (Δ13C) and nitrogen (Δ15N) in 22 teleost fishes, which together provided sufficient information to assess the effects of temperature, prey delta baseline (PDB), tissue-, prey-, and habitat-type on TDF. Overall adjusted means (± SE) of 3.1 ± 1.6‰ for Δ15N and 2.1±1.4‰ for Δ13C were close to previously published values for fishes. However, our results showed that Δ15N was affected by temperature, δ15NPDB, prey-type and tissue-type: Δ15N decreased by 1.6‰ as temperature increased from 4 to 27 °C, and by 4.3‰ when δ15NPDB increased from 1 to 15.5‰. Δ15N differences of 0.8 were found between tissue-type and 2.5‰ between prey-types. Δ13C was affected by both δ13CPDB and tissue-type: Δ13C decreased by 1.6‰ as δ13CPDB increased from − 26.9 to − 14.1‰, while Δ13C differed between tissue-types by 2.4‰. Evidence of prey-type and temperature effects upon Δ13C was unclear. Our results indicate that TDF variability caused by water temperature, PDB, and prey-type effects is sufficient to recommend not using universal mean TDF values for SIA applications for fish inhabiting particularly cold or warm habitats and/or consuming isotopically distinct prey. This review also highlighted the continued need for new, purposely-designed and properly reported experimental studies.