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

The isotope ratios of zinc (⁶⁶Zn/⁶⁴Zn expressed as δ⁶⁶Zn), a vital nutrient, increasingly demonstrate trophic discrimination among vertebrates, making δ⁶⁶Zn 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 δ⁶⁶Zn 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 δ⁶⁶Zn 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 δ⁶⁶Zn 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 δ⁶⁶Zn variability with values distinct from the pisciculture S. aurata, documenting a much more isotopically heterogeneous diet consumed by the wild individuals. Still, tissue–tissue δ⁶⁶Zn differences in wild-caught individuals are close to those observed in the pisciculture ones with progressively lower δ⁶⁶Zn values in the order bone > enameloid > white muscle. Our results demonstrate predictable tissue-diet and tissue-tissue δ⁶⁶Zn differences among fish hard and soft tissues and can be applied to identify the δ⁶⁶Zn values of dietary input, thereby informing trophic (palaeo)ecological reconstructions.