Tracing of aquaculture-escaped meagre Argyrosomus regius through otolith microchemistry

Escape incidents of farmed fish involve economic losses to fish farms, interactions with local fisheries and environmental impacts to coastal ecosystems. In order to ensure a sustainable aquaculture activity it is advisable to gather any kind of information about the escapees for further management strategies. In this study, we aimed to trace the life history of escaped meagre (Argyrosomus regius) through otoliths microchemistry, based on the assumption that escaped fish experience different environmental conditions once they are outside the net-pen compared to their farmed conspecifics. Strontium (Sr88) and barium (Ba138) composition was analyzed using laser-ablation ICP-MS along core-to-edge transects of right sagittal otoliths on escaped and farmed meagre from the same coastal area in the W-Mediterranean Sea. Overall, results showed similar patterns of Sr concentrations throughout the otolith transects between farmed and escaped meagre, although some differences can be observed at specific periods of fish life for Ba concentrations. Consequently, temporal variations regarding otolith Sr:Ba ratios differed between farmed and escaped meagre, suggesting that farmed and escaped fish shared the same origin (rearing at coastal farms) but inhabited in different conditions from a certain time of their life. However, core-to-edge Sr:Ba values also differed among escaped individuals, which might indicate that each individual escaped in different periods. Consequently, the otolith Sr:Ba ratio seemed to be a good indicator of differences between fish groups, showing different temporal patterns. Nevertheless, the limitation of the low number of sampled individuals prevented to draw clearer conclusions. Further research is necessary in order to investigate the potential use of otolith microchemistry as a practical tool to trace of escaped fish, and consequently, to help solving potential conflicts among coastal users improving management of potential negative socioeconomic and ecological impacts.