Stable isotope otolith fingerprint signatures: A mass marking technique for farmed salmon

Understanding the ecological and genetic effects of fish escapees from aquaculture facilities on wild fish stocks requires the ability to trace escapees. This is currently difficult due to the lack of a cost effective, mass... [ view full abstract ]

Understanding the ecological and genetic effects of fish escapees from aquaculture facilities on wild fish stocks requires the ability to trace escapees. This is currently difficult due to the lack of a cost effective, mass marking technique that differentiates wild from farmed fish and traces escaped fish back to the farm of origin. We investigated three stable isotope otolith fingerprint mark delivery techniques for mass marking farmed Atlantic salmon (Salmo salar) to determine if they could achieve unambiguous marks with 100% accuracy. Otolith fingerprint signatures created with enriched barium and strontium isotopes were delivered via: 1) Maternal transfer: where an isotope marker is injected into broodstock, and thus in turn passed on to the offspring; 2) Egg immersion: where fertilised eggs are left to swell in a solution containing an isotope marker; and 3) Vaccination: where the isotope marker is combined with a vaccine and injected into fish. Analyses of otolith signatures were carried out on a Varian Inductively Coupled Plasma Mass Spectrometer (ICP-MS) fitted with a HelEx (Laurin Technic and the Australian National University) laser ablation (LA) system constructed around a Compex 110 (Lambda Physik) excimer laser. 100% marking success was achieved with all three techniques at specific marker concentrations and all techniques are capable of creating marks that cannot be confused with marks in wild fish. Mark success was dependent on type, concentration, and combination of isotope markers used. In addition, no measurable side effects of stable isotope marking on fish growth, condition, or mortality were observed. Each technique can produce multiple fingerprint signatures for as little as 0.2 US cents per fish. We conclude that mass marking farmed Atlantic salmon with stable isotope otolith fingerprint signatures is a viable method to identify and trace farmed fish escapees.