Circular and sustainable aquaculture: the use of next-generation protein sources in fish feed

The challenge of obtaining high-quality protein is increasing because of socio-economic factors and environmental concerns surrounding protein production, including greenhouse gas emissions and biodiversity loss. Consequently, there's a growing demand for sustainably produced proteins. Aquaculture plays a crucial role in meeting this demand, but it faces challenges related to the depletion of fish meal (FM) stocks, leading to sustainability and economic concerns. During this doctoral research Hermetia illucens (HI) larvae meal and single-cell proteins (SCPs) from Torula yeast (TY) and Paecilomyces variotii (PV) were tested on gilthead sea bream. In the case of HI larvae meal, inclusion levels of up to 15% showed no negative effects on growth or feed efficiency. HI also positively impacted liver health and increased the abundance of beneficial gut microbiota. Additionally, it did not compromise the sensory, technological, or nutritional quality of sea bream fillets. For TY, inclusion levels of 5% and 7.5% resulted in optimal growth performance, improved blood enzyme function under challenging conditions, and promoted beneficial gut microbiota. Similarly, inclusion of SCPs from PV did not affect growth performance and improved gut microbiota diversity and metabolic activity. Both TY and PV SCPs showed potential as alternatives to fish meal, with PV SCPs also demonstrating probiotic qualities. In conclusion, HI larvae meal can effectively replace up to 15% of fish meal without compromising growth or feed efficiency, while also providing gut health benefits. TY and PV SCPs show promise as sustainable protein sources, with TY particularly beneficial at a 7.5% inclusion level. These findings underscore the potential of alternative protein sources to address sustainability challenges in aquaculture and warrant further investigation in this field.