Effects of body size and environment on diet-tissue δ13C fractionation in fishes

δ13C data are often used in trophodynamic research where diet-tissue fractionation (Δδ13C) is assumed to be 0-1‰ per trophic level and unaffected by the size of animals or their environment. Variation in Δδ13C will influence conclusions about food sources, energy pathways and trophic level. To assess the effects of body size, age and environmental conditions on Δδ13C, European sea bass (Dicentrarchus labrax) were reared on constant diets of dab (Limanda limanda) or (Ammodytes marinus) for 2years under natural environmental regimes. Bass were sampled approximately monthly to determine Δδ13C for muscle, heart and liver tissue and were 1.66‰, − 0.18‰, − 1.77‰ (sandeel diet) and 1.34‰, − 1.18‰, − 1.75‰ (dab diet) respectively. Arithmetic lipid correction increased Δδ13C to > 2‰ for muscle and liver. Δδ13C was dependent on body mass and experimental duration (age) and generally declined with weight or time even after correction for lipid content. For liver, increasing temperature increased Δδ13C. The Δδ13C estimates from this study were compared with all available published Δδ13C estimates for fish. Bass muscle Δδ13C was similar to previous estimates for fish white muscle Δδ13C (1.56 ± 1.10‰) and whole body Δδ13C (1.52 ± 1.13‰). Fractionations derived in this study, combined with those from the literature, support the use of diet-tissue fractionation values of between 1‰-2‰ for δ13C, rather than the commonly used 0‰ − 1‰. For muscle Δδ13C, 1.5‰ is appropriate.