Benefits of using an exogenous protease on performance, digestibility, and nitrogen excretion in European seabass (Dicentrarchus labrax) farming

Animal Feed Science and Technology

Ester Santigosa, Rui Rocha, Andreia Raposo and Jorge Dias.

https://doi.org/10.1016/j.anifeedsci.2026.117117

The trial evaluated the effects of three protease supplementation levels on growth performance, nutrient digestibility, and nitrogen excretion in European seabass (Dicentrarchus labrax). Four isonitrogenous, isolipidic, and isoenergetic diets, all based on a single basal formulation were tested: a control (CTRL) and three diets supplemented with protease at 100, 200, and 300 mg/kg (PRO100, PRO200, PRO300). Fish (initial weight 26.6 ± 1.7 g) were fed these diets for 90 days at 20.3 ± 0.4°C. Protease supplementation at 200 and 300 mg/kg significantly improved final body weight and specific growth rate compared to CTRL and PRO100 (p<0.05). These diets also led to lower feed conversion ratio (FCR) and higher protein efficiency ratio (PER) (p<0.05). Fish fed PRO200 and PRO300 showed significantly greater whole-body protein, fat, and energy retention (p<0.05). Regardless of dose, protease supplementation enhanced digestibility of protein, energy, and several amino acids (Arg, Lys, Thr, Val, Met, Asx, Ala, Pro) (p<0.05). Fish on PRO200 and PRO300 diets had significantly reduced non-ionised ammonia (NH₃) excretion, while all protease-supplemented diets lowered ionised ammonia (NH₄⁺) and total ammonia nitrogen (TAN) excretion (p<0.05). Overall, supplementation at 200 and 300 mg/kg improved growth and feed utilization and reduced measured nitrogen excretion under the conditions of this study. These outcomes indicate potential for improved production efficiency and lower nitrogen waste.