Abstract <p>Vaccine development for aquaculture is an urgent but difficultproblem, due to the diversity of fish and their pathogens, as wellas the specific features of fish immunity. The cultivation of valuablefish species in aquaculture conditions makes it possible to obtaina high-quality product free from infections all year round. Increasingthe efficiency of fish production in aquaculture through the useof antibiotics can lead to microbial resistance not only in fish,but also in the entire hydrobiocenosis. The development of immunobiologicalmedicines, including vaccines of various types, will reduce theuse of antimicrobial agents, but provide protection. Mammalian vaccinationprotocols are well developed and highly effective, but they arepoorly applicable for fish immunization due to significant differencesin the structure of the immune system. The immune system of bonyfish has a full-fledged innate immunity, in some ways even strongerthan that of mammals, and most of the elements of adaptive immunity. However,fish lack the lymph, corresponding lymphatic vessels, and lymphnodes that provide an effective adaptive mammalian response. Theaim of this review was to summarise and critically analyse literaturedata concerning the peculiarities of fish immune system structurein comparison with that of mammals. In addition, the review discussedvarious approaches to fish immunization and the mechanisms of actionof effective vaccines used in aquaculture.</p>