Dietary 1.3-1.6 yeast β-glucans enhance immune response and disease resilience in European seabass challenged with Tenacibaculum maritimum.

INTRODUCTION

Nutritional strategies have emerged as promising tools to modulate immune responses in marine fish, particularly at mucosal surfaces involved in host-pathogen interactions. Dietary immunomodulators such as yeast-derived β-glucans (BG) have gained attention for their capacity to enhance innate immune defenses, however their role in coordinating these mechanisms during bacterial infections remains incompletely understood.

METHODS

This study evaluated the effects of two dietary inclusion levels (0.06 and 0.12%) of purified yeast β-1,3/1,6-glucans on the immune responses of European seabass (Dicentrarchus labrax) following a bath challenge with Tenacibaculum maritimum specifically. After four weeks of feeding with experimental diets, fish were exposed to a sub-lethal infection, and immune parameters were accessed in the skin, intestinal mucosa and at systemic level.

RESULTS

Growth performance and feed efficiency were not affected by BG supplementation. At 24 h post-infection, fish fed with the 0.12% BG diet maintained circulating leukocyte counts and displayed increased plasma lysozyme activity, indicating enhanced early immune readiness. Moreover skin immune responses showed an early upregulation of pro-inflammatory and antimicrobial related genes, followed by increased expression of regulatory cytokines at 7 days post-infection, suggesting an efficient transition from immune activation to resolution. In contrast, intestinal immune responses remained largely unchanged, indicating a compartmentalized modulation focused on the primary site of infection.

CONCLUSION

Overall, dietary BG supplementation exerted a dose dependent immunostimulatory effect in European seabass, with 0.12% BG eliciting the most significant chances in disease resilience.