Design of sustainable aquafeed for freshwater and marine Recirculating Aquaculture Systems

This PhD thesis investigates the potential of different ingredients to optimise aquafeed formulations tailored for marine and freshwater recirculating aquaculture systems (RAS). Through a comprehensive approach, the study assesses raw material characteristics, diet digestibility, feed and waste properties, fish growth performance and health, fillet quality, and the economic viability of formulations. A general discussion integrates findings through a SWOT analysis, critically evaluating the strengths, weaknesses, opportunities, and threats of the tested dietary ingredients. The first study evaluates the digestibility, pellet characteristics, and nitrogen excretion of ten raw materials in greater amberjack (Seriola dumerili) reared in RAS. Diets including ingredients such as fishmeal, porcine haemoglobin, and soybean protein concentrate demonstrated the highest digestibility. Porcine haemoglobin and fishmeal achieved the highest protein ADCs, while potato protein and beet pulp exhibited the lowest. Pellet oil leakage, turbidity, and faecal properties varied significantly among diets, with fermented soybean, beer yeast with fat, and fishmeal producing less water turbidity and more stable faeces. These findings provide insights into sustainable aquafeed formulations for Mediterranean aquaculture species. The second study focuses on waste management strategies in rainbow trout (Oncorhynchus mykiss) fed diets incorporating fishmeal alternatives such as poultry by-product meal and hydrolysed feather meal. Results indicate that replacing fishmeal with poultry by-product meal improves nutrient digestibility and faecal retention but increases water turbidity when hydrolysed feather meal and rapeseed meal are used. Diets did not affect growth rates but influenced digestibility and faecal particle size, highlighting the potential of alternative proteins in waste management. The third study examines dietary inclusion levels of fishmeal and poultry protein blends in African catfish (Clarias gariepinus). Diets with reduced fishmeal and high poultry protein inclusion impaired protein and lipid digestibility, growth performance, and feed conversion. Conversely, a balanced inclusion of fishmeal (45 g kg⁻¹) and poultry processed proteins (280 g kg⁻¹) supported optimal growth and economic feasibility, underlining the potential of alternative proteins for sustainable RAS aquaculture. A bibliometric-informed SWOT analysis developed a prioritisation framework for ingredient selection in RAS aquafeeds. It highlights shifts in priorities over the last decade, including increased emphasis on water quality management and sustainable ingredient sourcing, while regulatory and processing concerns have stabilised. This framework guides manufacturers in developing resource-efficient, environmentally sustainable aquafeeds. Future research should explore raw material profiles and their effects on pellet stability, faecal properties, and nitrogen waste. Evaluations of low-fishmeal diets, particularly for salmonids, and the role of poultry proteins in omnivorous species could further advance cost-efficient and sustainable RAS feed formulations, ensuring scalability and ecological alignment.