Effect of temperature on 13C and 15N incorporation rates and discrimination factors in two North American fishes

Abstract

The biological parameters needed to interpret isotopic field data on food webs — namely isotopic incorporation and discrimination (Δ13C and Δ15N) — are unknown for many animals. We investigated the effects of temperature on carbon and nitrogen incorporation and discrimination in creek chub (Semotilus atromaculatus) and white sucker (Catostomus commersonii) by rearing wild-caught fish on a distinct diet at 12 and 20 °C for 160 days. Mass specific growth rates were higher at 20 °C. Isotopic turnover was mainly influenced by metabolic processes as opposed to growth in both species, especially white sucker. Cold-reared fish had slower rates of isotopic incorporation and higher isotopic residence times than warm-reared fish. Discrimination factors were generally smaller for Δ15N (range = 1.9 to 3.0) and larger for Δ13C (range = 1.4 to 2.3) than values reported for other fishes. Variable temperature effects on discrimination suggests unmeasured effects of the experimental diet which will require additional experimentation to tease apart. These results support the hypothesis that metabolic rates are correlated with isotopic incorporation rates in animals dependent on environmental temperature.