Introduction
Aquaculture is rapidly emerging as a vital sector in global food production. However, one of its persistent challenges is effective health management. Increasing fish stocking densities often lead to heightened stress levels, which in turn contribute to the outbreak of serious diseases. While antibiotics have traditionally been used to address these issues, their application is now heavily regulated or even banned in many regions. As a result, there is a clear need for alternative strategies to enhance immune responses in fish. One promising approach involves the use of β-glucans, which have been studied for their immunostimulatory effects in fish for several decades.
This presentation will highlight key findings on the use of β-glucans in fish, demonstrating increased survival rates across various species when challenged with a broad range of bacterial pathogens. Data will be presented for both cold-water and tropical fish species. We will also discuss recent advances regarding the role of β-glucans in wound healing - an important factor in disease proliferation - as well as their capacity to enhance vaccine efficacy in salmon. Notably, pre-vaccination intake of β-glucans has shown to improve immune responses to both bacterial and viral infections.
Additionally, we will present findings on the dose-response relationship of β-glucans in tilapia at both optimal and suboptimal water temperatures. These results suggest that water temperature influences how different dosages modulate the immune system. Lastly, we will explore how β-glucans can significantly alter lipid metabolism in fish. Altogether, this presentation aims to provide a comprehensive overview of the multifaceted benefits of incorporating this important additive into fish nutrition, positioning them as a natural, sustainable strategy for improving aquaculture health and performance.
Glucan is a general term used to describe a group of polysaccharide polymers that are classified based on the type of glycosidic linkage they contain—either β - or α -linked. β-glucans derived from different biological sources often exhibit variations in their primary structures and conformations. The primary structure is defined by the type of glycosidic bonds, degree of polymerization, and branching patterns. In contrast, β-glucans conformations can appear as random coils, single helices, or triple helices, depending on factors such as the primary structure, intermolecular interactions, temperature, and solvent conditions .
β-glucans are found across a wide range of organisms, including bacteria, algae, fungi, and plants, each source producing structurally distinct types. Typically, their structure consists of a backbone made up of β -(1,3)- and/or β -(1,4)-linked D-glucopyranosyl units arranged in a non-repeating but non-random manner, with variable side chains branching off the main chain. Because of this structural diversity, the immunomodulatory activity and effectiveness of different β-glucans molecules can vary significantly , even among those with similar molecular weights, structures, and conformations.
Numerous studies have explored correlations between β-glucans biological activity and their molecular structure, size, branching frequency, degree of chemical modification, conformation, and solubility. However, due to often inconsistent or contradictory findings, broad generalizations should be approached with caution. A wide range of concentrations and administration routes , including oral delivery , have been tested, yet no consensus has been reached regarding the optimal source, molecular size, or physicochemical characteristics of β-glucans for immunomodulatory purposes.
Method
This presentation will summarize nine recently published scientific articles from leading international journals. These studies were carefully selected to highlight the diverse approaches and applications of β-glucans in fish nutrition. The articles written by Roberti Filho et al 2019, Do-Huu et al 2016, Koch et al 2021 and Fronte et al 2019 will be highlighted in the presentation.
Results
The use of beta-glucan for fish:
Conclusion
To date, more than 3,000 studies have investigated the effects of beta-glucans on immune responses in fish. Despite this extensive body of research, several key questions remain unresolved. In particular, there is still limited understanding of the receptors involved in beta-glucan recognition and the downstream signaling pathways in teleosts. As a result, it remains unclear whether the observed immunostimulatory effects are due to direct action on leukocytes or indirect mechanisms—such as alterations in the gut microbiota composition.
Most existing studies have focused on short-term immune responses, typically lasting from a few days to several weeks. However, emerging research in innate immunity suggests that beta-glucans may also exert longer-lasting effects, potentially through a mechanism known as "trained immunity," which may provide prolonged enhancement of immune function.
References
Do-Huu H., H.M. Sang and N.T. Thanh Thuy, 2016. Dietary β -glucan improved growth performance, Vibrio counts, haematological parameters and stress resistance of pompano fish, Trachinotus ovatus Linnaeus, 1758. Fish Shellfish Immunol., 54: 402-410.
Fronte, B., Kim, C.H., Bagliacca, M., Casini, L., Zoysa, M. 2019. ß-glucans enhance tissue regeneration in zebrafish (Danio rerio): potential advantages for aquaculture applications Aquac. Res., 50, pp. 3163-3170
Koch, J.F.A., Oliveira, C.A.F., Zanuzzo, F.S. 2021. Dietary β-glucan (MacroGard®) improves innate immune responses and disease resistance in Nile tilapia regardless of the administration period . Fish & Shellfish Immunology, 112, 56-63. 1,3-1-6
Roberti Filho, F. O., Koch, J.F.A., Wallace, C., Leal, M.C., 2019. Dietary β-1,3/1,6-glucans improve the effect of a multivalent vaccine in Atlantic salmon infected with Moritella viscosa or infectious salmon anemia virus. Aquacult Int 27, 1825–1834.