Environmental impact of aquafeed for rainbow trout containing alternative protein meals

The study analysed the effect on global warming potential (Life Cycle Assessment) of the partial replacement of fishmeal (from by-products) by alternative protein meals in diets for rainbow trout. A total of 1020 trout (17±7.5 g) were fed four diets (three tanks per diet) with fishmeal being partially substituted by alternative protein meals: a control diet (FM) with 307 g/kg fishmeal and three alternative diets where about 40% of fishmeal was replaced with poultry by-product meal (diet PBM), feather meal (diet FeM), or feather + rapeseed meals (diet FeM+RM). All diets contained also rapeseed oil, soybean protein concentrate and bacterial protein meal, among other ingredients. Final weight (191 g) and feed conversion ratio (1.05) did not differ among diets. The system boundaries included the impact of aquafeed production; 1 kg increase of fish was used as functional unit. Global warming potential, without (GWP) and with (GWP_LUC) emissions due to land-use change were calculated. Impact values were analysed by ANOVA with diet as a fixed effect. No differences among diets were found in term of GWP (1.74±0.07 kg CO2-eq, on average) and GWP_LUC (2.75±0.10 kg CO2-eq). In all diets, the major contribution to global warming was due to ingredients different from the four protein meals tested, i.e. rapeseed oil (25% and 31% of the total impact for GWP and GWP_LUC), followed by soybean protein concentrate (10% and 23%) and bacterial protein meal (20% and 12%). Among the protein meals tested, fishmeal provided the highest contribution (14% GWP and 9% GWP_LUC), while the contribution of the three alternative protein meals was limited (0.3% and 0.3% for poultry by-product meal; 2.8% and 1.8% for feather meal; 1.7% and 1.4% for rapeseed meal). In conclusion, the tested alternative protein meals are promising and sustainable ingredients for trout aquafeeds guaranteeing good growth rates and, compared to fishmeal from by-products, a lower contribution to global warming.