LCA to evaluate the environmental opportunity cost of biological performances in finfish farming

Purpose Mortality and suboptimal biological performance are a widespread problem in finfish farming. The associated losses constitute an environmental opportunity cost that needs to be thoroughly assessed to prioritize actions aiming at reducing the environmental impacts of finfish aquaculture. We here propose and demonstrate the use of a new parameterized and consequential LCA model of sea-trout production designed to assess the environmental opportunity costs of suboptimal biological performances, considering distinct mortalities and biological feed conversion ratios (FCRs) along the rearing process. Methods Primary data was collected in Danish and Italian farms to reconstitute the whole production process for sea-reared trouts. The level of detail allowed us to divide this production into seven different growth stages for which mortality and biological FCR can be assessed and modified. Excretion and valorization of fish sludge were modeled with a calibrated mass-balance model. Together with fish sludge, dead fish was modeled as valorized by anaerobic digestion. The foreground system was linked to the consequential version of ecoinvent 3.8 for which the embedded uncertainty was considered in Monte Carlo simulations. The model was used to assess the current environmental opportunity costs and evaluate the effect of losses happening at different timings along the rearing process. Results and discussion Results showed a low environmental opportunity cost for the current mortality rate of 5% as suppressing this mortality decreased impacts by 3.5 to 5% across impact categories. Decreasing the biological FCR decreased the environmental impacts proportionally. The timing of the losses was shown to greatly influence the environmental opportunity cost, and the same mortality rate happening in the late stages had substantially more impact than in the first stages. The valorization of the dead fish showed a negligible contribution to the reduction of impacts in the current system but showed a substantial contribution in the case of higher mortalities, such as observed for other farms and foreseen in the future. Conclusion The model demonstrated that assessing an opportunity cost by multiplying the lost biomass by a unique impact factor constitutes an oversimplification neglecting the losses timing and the fact that fish biomass is not a marketable product. Even though the current environmental opportunity cost for losses appeared neglectable, suboptimal biological FCR should be tackled. The model and approach can be used to project trout farming within future disease regimes and assess the trade-offs regarding fish health issues and new treatments and practices.