The growing need for sustainable aquafeeds has driven the search for alternatives to marine-derived ingredients. This study evaluated the effects of novel diets including poultry by-product meal and Hermetia illucens (black soldier fly) larvae meal on growth performance, fillet yield, proximate composition, mineral profile, and fatty acid composition of gilthead sea bream (Sparus aurata) and European sea bass (Dicentrarchus labrax) reared under commercial sea-cage farming conditions. In gilthead sea bream, the test diet led to a significantly higher final body weight, specific growth rate, improved feed conversion ratio, and greater fillet yield, along with elevated levels of n-3 polyunsaturated fatty acids. In contrast, European sea bass exhibited similar growth performance across diets, but fish fed the test diet containing farmed salmon oil as the primary lipid source, had lower EPA and DHA content and higher saturated fat levels. Still, fillet yield was higher, and fatty acid profiles across both species remained within the recommended limits for human consumption. These findings demonstrate that alternative feeds based on terrestrial ingredients can sustain or enhance performance and fillet quality in Mediterranean aquaculture species, supporting broader efforts toward environmental sustainability and human nutrition through the maintenance of beneficial n-3 polyunsaturated fatty acids levels.
