Adjuvants for Fish Vaccines

The accelerated incidence of infectious diseases in the aquaculture system is usually associated with high mortality and morbidity rates with increased economic loss to the aqua farmers. This has led to the extensive application of a wide range of chemicals, antibiotics and drugs to mitigate these diseases in aquaculture system. However, unregulated use of these chemicals has become a serious issue to both the host and human health. In this prelude, suitable prophylactic measures like vaccination have become an important strategy in controlling diseases for sustainable aquaculture. Vaccines are of several types and administered in different ways; each has its pros and cons based on their action, persistence and efficacy considering the medium in which host thrives. Therefore, the combination of adjuvants with a potential antigen for vaccination will have several beneficial effects, including prolonging antigen release, aiding in activating and releasing co-stimulatory signals, enhancing local inflammation, and activating lymphocytes proliferation. The most widely used adjuvant is Freund's complete adjuvant (FCA) and others like Freund's incomplete adjuvant, oil emulsions, montanides, minerals, nano/microparticles adjuvants, immune-stimulating complexes lipopeptides and saponin, etc., which have also explored fish vaccination. However, further research is required for the advancement of these adjuvants for use in fish vaccination. This chapter deals with adjuvant types, their mechanism of action, and their role in heightening the immune responses of the vaccinated fish in the aquaculture system.