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

Sulphur isotope analysis (delta(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 delta(34)S data. To investigate the effects of temperature, ration, body size and age on sulphur trophic fractionation (Deltadelta(34)S) in fish, we reared European sea bass (Dicentrarchus labrax) on identical diets at 11 and 16 degrees C at three ration levels for over 600 days. Deltadelta(34)S was between 0 and -1 per thousand. The effect of temperature on Deltadelta(34)S was small and inconsistent, varying over the course of the experiment and depending on ration. This contrasts with temperature effects on bass Deltadelta(13)C and Deltadelta(15)N, where Deltadelta(13)C increases at warm temperatures while Deltadelta(15)N falls. Body size and age had a positive relationship with Deltadelta(34)S but the relationship with size was not significant for bass that weighed >20 g. As Deltadelta(34)S is small and the range in delta(34)S of potential diet items can be much greater than the range in delta(13)C or delta(15)N, our results show that sulphur stable isotopes are particularly useful for source differentiation in fish.