Adjuvants for vaccines aid in boosting the immunogenicity of weak antigens. When the adjuvant action of some compounds was discovered in the 1940s of the previous century, a great deal of adjuvants from various chemical groups were researched. The most often utilized adjuvants in aquatic vaccinations are oil ones. Oil adjuvants such as aluminum salts and granules are considered as Antigen-recurrent adjuvants which, to stimulate an immune response to antigens, are often delivered to the immune system by membrane fusion, endocytosis, and pinocytosis. Oil adjuvants can enhance vaccine effectiveness by stimulating antibody production and T-cell immune response. They can reduce immunization doses, lowering vaccine costs. They extend immunity duration, providing longer-lasting protection against diseases. However, they can cause reactogenicity, causing pain and inflammation at the injection site, and may not stimulate adequate T-cell response, potentially compromising vaccine effectiveness. The SEPPIC-developed MONATINE series of mineral oil-based adjuvants is a popular choice for fisheries vaccines due to its low viscosity, easy emulsification, stability, and safety during absorption. Therefore, careful consideration and use of oil adjuvants are crucial for effective vaccines. The particular efficiency of oil adjuvants in this context varies based on the vaccination and the target aquatic species, although adjuvant effectiveness in aquatic vaccines is still a topic of current study
