Life cycle assessment of Hermetia illucens meal inclusion in diets for trout reared in aquaponics

This study analysed the effect on global warming potential (life cycle assessment method, LCA) of the inclusion of a partially defatted Hermetia illucens larvae meal (HI) in diets for rainbow trout (Oncorhynchus mykiss) reared in a low-tech aquaponic system. Three inclusion levels were tested: 0%, 6% and 12% (HI0, HI6, HI12, respectively), for a fishmeal replacement of 0%, 25% and 50%, respectively. A total of 173 rainbow trout (initial live weight: 156±39.8 g) were distributed among nine experimental aquaponic units and fed the experimental diets for 76 days. At the end of the trial, no differences among fish fed the different diets were found in terms of mortality (3% on average), final weight (303 g) and feed conversion ratio (1.53). The LCA reference unit was the aquaponic unit and the system boundaries were set to include the impact due to aquafeed production; 1 kg increase of rainbow trout was used as functional unit (FU). Impact categories were global warming potential, without (GWP) and with (GWP_LUC) emissions due to land-use change. Emission factors related to HI production (EFHI) were derived from literature (9 studies; 20 values). Considering the control diet (HI0), the mean GWP and GWP_LUC generated to produce 1 FU were 1.32±0.08 and 3.36±0.21 kg CO2-eq, respectively. Mean GWP per 1 FU (calculated using the different EFHIs) increased by 32% and 48% with HI6 and H12 diets compared to HI0 diet; mean GWP_LUC increased by 10% and 13%, respectively. The GWP values obtained in HI12 compared to HI0 diet changed according to EFIH from -1% to 31% (GWP) and from -10% to +55% (GWP_LUC). In HI12 diet, only 5 of 20 (GWP) and 8 of 20 (GWP_LUC) EFHI determined GWP equal or lower than that associated with HI0 diet. In conclusion, based on literature EFHI, a reduction in GWP in rainbow trout fed HI still need to be confirmed and likely requires the identification of technical hotspots in HI production.