Evaluation of a commercial mushroom-derived product as a dietary immunomodulator and its effects on disease resistance in European seabass (Dicentrarchus labrax) juveniles

The use of natural bioactive ingredients is a promising strategy to improve fish health and enhance disease resistance in sustainable aquaculture. The present study evaluated the effects of dietary supplementation with Hifas Aqua , a mushroom-derived product containing Pleurotus ostreatus , Lentinula edodes , and Herimax ® (fermented Hericium erinaceum mycelium), on the immune response and disease resistance in European seabass ( Dicentrarchus labrax ). Fish were fed experimental diets containing 0.2, 0.4, 1 and 2% Hifas Aqua (HA0.2, HA0.4, HA1.0 and HA2.0, respectively) for 110 days, after which a challenge with Photobacterium damselae subsp. piscicida was performed. Dietary supplementation significantly upregulated the expression of several cytokine genes and antimicrobial- and iron metabolism-related genes at 110 days post dietary treatment, particularly in fish fed the HA1.0 and HA2.0 diets ( p < 0.05). Furthermore, supplementation increased the expression of adaptive immunity-related markers ( mhcI, mhcII, cd4 , and cd8 ), particularly in fish fed HA0.4, HA1.0 and HA2.0 diets ( p < 0.05). These molecular changes were accompanied by increased plasma lysozyme, peroxidase, and bactericidal activities, indicating the activation of humoral innate defenses together with immune pathways associated with cellular responses. Following the experimental challenge with P. damselae subsp. piscicida , fish fed the highest inclusion levels of Hifas Aqua (HA1.0 and HA2.0) exhibited significantly higher survival rates than those in the control groups ( p < 0.05). The higher survival of fish fed HA1.0 and HA2.0 coincided with increased plasma lysozyme, peroxidase and bactericidal activities at 2 days post challenge, without additional upregulation of the measured inflammatory cytokine transcripts at that time point. Overall, the results indicate that Hifas Aqua modulated innate and adaptive immune-related pathways and was associated with improved survival following P. damselae subsp. piscicida challenge in European seabass. These findings support the application of mushroom-derived bioactive compounds as sustainable functional feed ingredients to improve fish health and increase resistance to bacterial pathogens in aquaculture.