Effect of temperature, ration, body size and age on sulphur isotope fractionation in fish

Sulphur isotope analysis ( δ 34 S) is increasingly identified as a valuable tool for source differentiation and the determination of trophic level in food webs, but there are still many uncertainties associated with the interpretation of δ 34 S data. To investigate the effects of temperature, ration, body size and age on sulphur trophic fractionation (Δ δ 34 S) in fish, we reared European sea bass ( Dicentrarchus labrax ) on identical diets at 11 and 16°C at three ration levels for over 600 days. Δ δ 34 S was between 0 and −1‰. The effect of temperature on Δδ 34 S was small and inconsistent, varying over the course of the experiment and depending on ration. This contrasts with temperature effects on bass Δ δ 13 C and Δ δ 15 N, where Δ δ 13 C increases at warm temperatures while Δ δ 15 N falls. Body size and age had a positive relationship with Δ δ 34 S but the relationship with size was not significant for bass that weighed >20 g. As Δ δ 34 S is small and the range in δ 34 S of potential diet items can be much greater than the range in δ 13 C or δ 15 N, our results show that sulphur stable isotopes are particularly useful for source differentiation in fish. Copyright © 2007 John Wiley & Sons, Ltd.