Introduction
Aquaculture is one of the fastest-growing food-producing sectors worldwide, but its expansion is heavily constrained by infectious diseases. Preventive approaches that strengthen host defenses are essential, and particularly against Tenacibaculum maritimum infection, a major threat to marine finfish aquaculture. Functional feeds incorporating bioactive additives such as ���-glucans have shown interesting results in terms of fish immunity modulation and pathogen resilience. However, the capacity of β-glucans to coordinate mucosal and systemic responses during a T. maritimum infection remains underexplored. This study aims to investigate the immunomodulatory effects of dietary ���-glucans in European seabass and following a T. maritimum challenge, assessing both mucosal and systemic immune responses.
Materials and Methods
European seabass (Dicentrarchus labrax) juveniles, having an initial mean body weight of 11.3 g were randomly distributed among 24 tanks (8 tanks per dietary treatment) and were fed with a diet containing 0, 0.06 or 0.12% of purified 1.3-1.6 yeast ���-glucans (BG). After 4 weeks of feeding, 4 replicated tanks per dietary treatment were subjected to a Tenacibaculum maritimum infection by bath inoculation while the other 4 tanks per treatment were used as non-infected control. Zootechnical parameters were monitored during the first 4 weeks of feeding. Mortality was recorded throughout the experiment. At 24h and 7 days post-infection, fish immune response was evaluated through mRNA expression levels of immune-related genes in skin and posterior intestine. Those analyses were complemented by measurement of some plasma immune-related parameters, including specific IgM against T. maritimum at 3 weeks following infection.
Results and Discussion
Growth performance and feed utilization were not affected by dietary BG supplementation. However, BG modulated systemic and mucosal immune responses following T. maritimum infection. At 24 h post-infection, the 0.12% BG diet maintained circulating white blood cell levels (p < 0.05) and increased plasma lysozyme activity in infected fish (p < 0.05), indicating enhanced early immune readiness. Specific IgM against T. maritimum also increased in both BG-fed fish groups 3 weeks after challenge (p < 0.05), suggesting enhanced adaptive immunity. In the skin, the 0.12% BG diet promoted an early upregulation of pro-inflammatory and antimicrobial-related genes at 24h post-infection (p < 0.05), followed by an increased expression of regulatory cytokines (il10 and tgfb) at 7 days post-infection (p < 0.05), indicating a balanced immune response. Multivariate analysis highlighted the skin as the primary responsive interface. In contrast, intestinal immune regulation was more controlled, with il10 expression reduced in infected fish fed the 0.12% BG diet at 7 days post-infection (p < 0.05).
Conclusion
These results demonstrate that dietary yeast BG can enhance localized (in skin) and systemic immunity in European seabass, in the context of a T. maritimum challenge, without compromising growth. The highest dose tested, 0.12% BG, was the one inducing the most significant enhancements in disease resilience.
Acknowledgment
This work received funding by national funds through FCT – Funda����o para a Ci��ncia e a Tecnologia, I.P., and by the European Commission's Recovery and Resilience Facility, within the scope of UID/04326/2025 and UID/04423/2025, UID/PRR/0423/2025 and UID/PRR/04326/2025, UID/PRR/04423/2025 and LA/p/0101/2020. MC also received funding from FCT through 2021.06497.BD.