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 (Delta C-13) and nitrogen (Delta N-15) 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 parts per thousand for Delta N-15 and 2.1 +/- 1.4 parts per thousand for Delta C-13 were close to previously published values for fishes. However, our results showed that Delta N-15 was affected by temperature, delta N-15(PDB), prey-type and tissue-type: Delta N-15 decreased by 1.6 parts per thousand as temperature increased from 4 to 27 degrees C, and by 4.3 parts per thousand when delta N-15(PDB) increased from 1 to 15.5 parts per thousand. Delta N-15 differences of 0.8 were found between tissue-type and 2.5 parts per thousand between prey-types. Delta C-13 was affected by both delta C-13(PDB) and tissue-type: Delta C-13 decreased by 1.6 parts per thousand as delta C-13(PDB) increased from - 26.9 to - 14.1 parts per thousand, while Delta C-13 differed between tissue-types by 2.4 parts per thousand. Evidence of prey-type and temperature effects upon Delta C-13 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.

Automated summary

Stable isotope analysis is widely utilized for assessing animal diet and movements, but relying on universal TDF values may overlook important factors such as temperature, prey type, and tissue type. This study compiled experimental TDF measurements for 22 teleost fishes, revealing significant effects of temperature, prey type, and tissue type on TDF values, indicating the necessity of considering these factors in future SIA applications for fish.