Immunomodulatory activity of -glucans in fish: Relationship between -glucan administration parameters and immune response induced

Diseases outbreak caused by pathogenic organisms is known to be one of the significant constraints faced by fish farmers and consequently pose great damage to the economy of the aquaculture sector. Vaccines and antibiotics are used to prevent the spreading of infectious diseases. However, these practices are cost-ineffective and may increase the resistance of pathogens towards antibiotics. Therefore, the use of immunostimulants in aquaculture as an alternative to antibiotics and vaccines is becoming popular nowadays. The selection of a suitable and effective immunostimulant for fish is essential to protect them against the pathogens. beta-glucan, a potent immunostimulant, is widely used in aquaculture to improve the immune system of fish. beta-glucan is a highly conserved carbohydrate that can be found in the cell wall of yeast, fungi, plant and even some bacteria species. The immunomodulatory role of beta-glucans on fish immunity are well identified in aquaculture research, whereby it was mainly investigated through the regulation of cellular and humoural immune parameters, immune-related genes and proteins expression, and resistance towards various infectious diseases. This review summarizes the recent literature on the mode of action of beta-glucans in fish immunity via a different route of administration. The suitable dose, duration and frequency of beta-glucans administration for optimal stimulation in different species of fish, as well as the combinational used of beta-glucans with one or more immunostimulants, were also highlighted.