Effects of size and diet on stable hydrogen isotope values (δD) in fish: implications for tracing origins of individuals and their food sources

Recent studies suggest that stable hydrogen isotope ratios (delta D) of fish can be used to track their watershed origin and the relative contributions of source material. Both applications assume that there is no metabolic or trophic effect on tissue delta D. We studied the local variation of delta D values in four fish species of contrasting size and feeding habits in an isotopically homogenous reservoir (Flix, Spain). Other isotopic values (delta N-15, delta C-13) and trace metal content were measured as indicators of trophic and bioaccumulation patterns. In addition, isotopic values (delta D, delta N-15, delta C-13) of other food web components were measured for comparison. Muscle delta D values differed greatly among fish species: European catfish, Silurus glanis (-131 parts per thousand); common carp, Cyprinus carpio (-141 parts per thousand); rudd, Scardinius erythrophthalmus (-158 parts per thousand); and roach, Rutilus rutilus (-163 parts per thousand). The influence of fish size and trophic position affected the fish delta D values. Possible mechanisms that drive delta D variation among fish might be a metabolic effect and (or) the compounding effect of ambient water delta D on exchangeable H at each trophic stage. Our findings showed that size and feeding habits are factors that should be controlled when tracing origins of fish or their dependence on nutrient inputs using delta D measurements.