Nutritional enhancement of lupin meal (Lupinus albus), through fermentation with Saccharomyces cerevisiae, as plant protein ingredient in aquafeeds for the European sea bass (Dicentrarchus labrax).

Legumes contain antinutritional factors that restrict their use in fish nutrition, however, biotechnological methods such as solid-state fermentation can improve their nutritional profile, positioning them as a sustainable alternative for aquafeed formulation. This research evaluated the feasibility of replacing soybean meal with Saccharomyces cerevisiae -fermented lupin meal ( Lupinus albus ) in feed formulations for European sea bass ( Dicentrarchus labrax ). Four diets were produced; one commercial type diet (FRL0) and three diets with partial (FRL10, FRL12.5) or complete (FRL15) replacement of soybean meal by fermented lupin meal. European sea bass juveniles, with an initial average weight: 18.9 g, were fed the experimental diets for 71 days in triplicate groups. Results indicated no adverse effects on key production indices when soybean meal was replaced partially or totally. Fermented lupin meal linearly improved feed utilization. Apparent digestibility coefficient of protein significantly increased in groups fed 12.5 % and 15 % fermented lupin, as did apparent digestibility coefficient of fat, compared to the FRL0 group. Trypsin activity in pyloric caeca was statistically elevated in the fermented lupin groups compare to FRL0 group. Whole-body composition, amino acid content, and deposition showed no significant differences among groups. Fermented lupin did not suppress the immune system, and a slight immunostimulatory effect was observed at a 12.5 % inclusion level. No histopathological alterations were detected. Overall, the results demonstrated the efficacy of solid-state fermentation process in enhancing lupin meal, highlighting its potential as a sustainable replacement for soybean meal in feed formulations for Mediterranean marine aquaculture species such us D. labrax . • First successful use of fermented lupin to replace soybean in sea bass diets • Linear improvement in FCR with inclusion of fermented lupin meal. • High and moderate levels of fermented lupin meal increased nutrient digestibility. • Increased trypsin activity in all groups treated with fermented lupin meal. • Fermented lupin meal at 12.5 % inclusion provided immunostimulatory effects.