Estimation of mercury uptake efficiency and the development of feed input models for the evaluation of baitfish regimes in determining mercury concentration of farmed southern bluefin tuna (Thunnus maccoyii)

A model is presented for the prediction of mercury (Hg) concentrations in the edible tissues of farmed southern bluefin tuna, Thunnus maccoyii (SBT) during commercial culture. The predictive model was developed using the initial Hg concentration of wild-caught SBT (mg kg− 1), Hg concentration of feed (mg kg− 1), SBT feeding rate (kg kg− 1 day− 1), SBT tissue growth rate (kg day− 1) and least squares minimisation estimation of Hg uptake efficiency, η. Model development and validation was based on experimental data collected from commercially cultured SBT which are farmed in in-sea pontoons (sea-pontoons). Model predictions indicate that over a typical farming season SBT from each of three commercially operated sea-pontoons experienced a 0.1 mg kg− 1, 0.14 mg kg− 1 and > 0.2 mg kg− 1 reduction in the Hg concentration of muscular tissues respectively. This is the first study to attempt to estimate Hg uptake efficiency in a tuna species. Estimation of Hg uptake efficiency and development of a working model for prediction of Hg concentration in SBT under varying culture diets, represent the first steps towards taking the guesswork out of managing Hg residues in cultured tuna.

► A model for prediction of Hg concentration in farmed SBT is presented and validated. ► Hg uptake efficiency (more closely resembling Hg uptake and retention) was estimated. ► Hg concentration was predicted to decrease by 0.1 to 0.2 mg kg–1 over a farming season. ► Mercury concentration is thought to reduce due to tissue growth dilution.