Immunostimulants are valuable for the control of fish diseases. At present, it has already been a main tendency to discover and develop novel immunostimulants with characteristics of low toxicity, high efficacy, immediate efficacy and long-term efficacy. In this review, the definition, defense mechanism, categories and application of fish immunostimulants are introduced and fish immunostimulants are classified systematically according to their sources. Moreover, the latest literature about fish immunostimulants in detail were presented and reviewed and three methods for control of fish disease were compared: vaccination, chemotherapy and immunostimulants. Fish immunostimulants were thought to be safer than chemotherapeutics and their range of efficacy was wider than vaccination. They may be able to compensate for these limitations of chemotherapeutics and vaccines, thus they hold tremendous potential for use in fish culture to reduce losses from fish diseases. Meanwhile, concepts of use of fish immunostimulants were presented and principles for use were also noted. For aquaculture, this review provided a scientific reference for control of fish disease by immunostimulants.
