Distinguishing hatchery from wild produced fish based on elemental chemistry of otoliths.
Stocking of hatchery-produced fish is an integral component of fisheries management with applications for recreational and commercial fisheries, as well as conservation of threatened species. Once stocked, it is often difficult to distinguish hatchery-produced from wild-produced fish. We aimed to determine if natural elemental signatures can be used to distinguish hatchery from wild fish in rivers where stocked fish were marked with alizarin complexone; hence, the accuracy of otolith chemistry to correctly classify fish could be assessed. We predicted that the edge of the otoliths of the two groups (alizarin marked hatchery fish and wild fish) would be similar since the fish were caught at the same time from the same place, and that the centre of the otolith would differ given that the two groups of fish would have spent their early life in different waters (hatchery vs river). In addition, we also predict that the centre otolith chemistry of stocked fish would match that of Narrandera hatchery fish, since this was their origin. Results showed that the edge otolith chemistry was similar between the two groups of fish, and that the centre otolith chemistry differed. As expected, the centre otolith chemistry of stocked fish matched that of Narrandera fish. We then analysed the edge and centre of otoliths of fish collected from Billabong Creek, where around 100,000 un-marked fish had been stocked to determine which fish were stocked fish. Results showed that virtually all fish were from Narrandera hatchery. Information on the proportion of hatchery produced versus wild produced fish is essential for assessment of fish populations.