Osmotic induction improves batch marking of larval fish otoliths with enriched stable isotopes

Otolith marking with enriched stable isotopes via immersion is a recent method of batch marking larval fish for a range of research and industrial applications. However, current immersion times and isotope concentrations required to successfully mark an otolith limit the utility of this technique.Osmotic induction improves incorporation and reduces immersion time for some chemicalmarkers, but its effects on isotope incorporation intootoliths areunknown.Here,we tested the effects of osmotic inductionovera rangeof different isotope concentrations and immersion timeson relative mark success and strength for Mg:Mg, Sr:Sr and Ba:Ba on Atlantic salmon (Salmo salar) larvae. 71% and 100% mark success were achieved after 1 h of immersion for Sr (75 mg L) and Ba (30 mg L) isotopes, respectively. Compared with conventional immersion, osmotic induction improved overall mark strength for Sr and Ba isotopes by 26–116%, although this effect was only observed after 12 h of immersion and predominately for Sr. The results demonstrate that osmotic induction reduces immersion times and the concentrations of isotope required to achieve successful marks. Osmotically induced isotope labels via larval immersion may prove a rapid and cost-effective way of batch marking fish larvae across a range of potential applications.