Zinc isotope composition of enameloid, bone and muscle of gilt-head seabreams (Sparus aurata) raised in pisciculture and their relation to diet

Abstract

The isotope ratios of zinc ( 66 Zn/ 64 Zn expressed as δ 66 Zn), a vital nutrient, increasingly demonstrate trophic discrimination among vertebrates, making δ 66 Zn a valuable dietary proxy for ecological, archaeological, and palaeontological studies. Given the novelty of the methodology, tissue-diet and tissue-tissue zinc isotope fractionation factors remain poorly understood and have so far only been studied in a few terrestrial mammals. Here, we investigate δ 66 Zn compositions of enameloid, bone, and white muscle of seven artificially-fed pisciculture gilt-head seabreams ( Sparus aurata ) from offshore Israel, in comparison to the Zn isotope composition of their diet. In addition, we also analysed δ 66 Zn values in the same tissues of wild-caught S. aurata , bluespotted seabream ( Pagrus caeruleostictus ) and grey triggerfish ( Balistes capriscus ) caught off the coast of Israel. We determine a tissue-diet δ 66 Zn offset for Sparus aurata of − 0.04 ± 0.09 ‰ (2SD) for bone, − 0.29 ± 0.06 ‰ (2SD) for enameloid, and − 0.45 ± 0.07 ‰ (2SD) for white muscle. Wild-caught fish have much higher among-individual δ 66 Zn variability with values distinct from the pisciculture S. aurata , documenting a much more isotopically heterogeneous diet consumed by the wild individuals. Still, tissue–tissue δ 66 Zn differences in wild-caught individuals are close to those observed in the pisciculture ones with progressively lower δ 66 Zn values in the order bone > enameloid > white muscle. Our results demonstrate predictable tissue-diet and tissue-tissue δ 66 Zn differences among fish hard and soft tissues and can be applied to identify the δ 66 Zn values of dietary input, thereby informing trophic (palaeo)ecological reconstructions.

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