Abstract

Otolith chemistry is widely used to address key questions relating to fish ecology and fisheries management; however, there is limited research on the relative contributions of water and diet to elements within otoliths. This study explicitly tested the proportional contributions of water and diet in 3 Australian freshwater fish—silver perch, golden perch and Murray cod—in a controlled laboratory experiment. We independently 'spiked' both tank water and diet with enriched stable isotopes of strontium ( 86 Sr) and barium ( 137 Ba), key elements used in otolith chem- istry. Hatchery-sourced fingerlings were used in the experiment and were independently exposed to a control, water-spiked or diet-spiked treatment for a period of 31 to 39 d. Otolith material laid down during the experiment was subsequently analysed for relevant isotopes using laser ablation inductively coupled plasma-mass spectrometry (LA ICP-MS), and water and diet samples were analysed using solution-based ICP-MS. An isotope mixing model was used to determine the rela- tive contributions of water and diet to Sr and Ba otolith chemistry. For all species, water was the dominant source of elements in the otoliths, contributing between 64 and 71% for Sr and 88 and 92% for Ba. Diet contributed to a far lesser degree, with contributions ranging from 4 to 6% for Sr and 10 to 26% for Ba. The results from this study improve interpretations of otolith chemistry data in freshwater fish, thereby allowing more accurate reconstructions of the environmental and movement histories of wild populations.

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