Towards circularity in aquaculture systems: Environmental impact of Hermetia illucens meal inclusion in diets for rainbow trout reared in aquaponics

In advancing towards more sustainable aquaculture, the inclusion of insect meals in aquafeeds has significant potential to increase circularity and reduce environmental impacts, especially in aquaponics. Nevertheless, there is a lack of information regarding the environmental performance of these innovative feeding and management solutions. This study assessed the environmental impact associated with the dietary inclusion of Hermetia illucens (HI) meal (0%, 6% and 12%) in diets for rainbow trout (Oncorhynchus mykiss) reared in a low-tech aquaponic system characterised by nine independent experimental units (6.06 kg/m3 of fish and 14 strawberry plants per unit). A cradle-to-gate attributional life cycle assessment model was used to consider the impacts related to the whole aquaponic system (AQ-FISH) and those only related to the production and use of the aquafeed (AQ-FEED). The impact categories were 100-year global warming (kg CO2-eq) – with (GWP_LUC) and without (GWP) the emissions associated with land-use change (LUC), acidification (AP, g SO2-eq) and eutrophication (EP, g PO4-eq) potentials, cumulative energy demand (CED, MJ), land occupation (LO, m2 /y) and water scarcity (WS, m3 -eq). The functional unit was a 1 kg live weight increase of rainbow trout. Data originated from a previous 76-d fish performance trial. Data regarding HI meal were derived from an interview with the manufacturer. An economic method was used to partition the impacts between HI meal, HI fat and the frass (exhausted substrate). The effect of the HI meal inclusion level on the AQ-FISH and AQ-FEED impact values was tested using one-way analysis of variance. A 1 kg live weight increase of rainbow trout reared in the aquaponic system (AQ-FISH) produced 15.6 kg CO2-eq (GWP), 18.3 kg CO2-eq (GWP_LUC), 67 SO2-eq and 55 g PO4-eq and used 354 MJ, 3.5 m2 /y and 311 m3 -eq. The dietary inclusion of HI meal did not affect the AQ-FISH results, except for CED (+2%–5%). When considering the impact resulting from feed production (AQ-FEED), the inclusion of HI meal did not affect GWP_LUC, AP, EP and LO, but it negatively affected GWP (+13%–26%) and CED (+34%–68%). Results from AQ-FISH and AQFEED scenarios showed low sensitivity to the methodological choices. Overall, our findings suggest that general improvements to reduce the environmental impact associated with rainbow trout production in aquaponics should be concurrently directed towards both the system setting and management, as well as towards the HI meal production process, with a particular emphasis on enhancing energy efficiency. To minimise potential trade-offs, especially from an environmental perspective, future studies should prioritise the investigation of energy use and greenhouse gas emission associated with feed production. This requires a thorough evaluation of all changes in the diet formulation resulting from the inclusion of a new ingredient.