APPLICATION OF IMMUNOSTIMULANTS IN AQUACULTURE: A REVIEW

Abstract

Immunostimulants enhance the humoral and cellular response in both specific and non-specific ways. These agents are widely used for impaired immune function and to stabilize the improved immune status. The use of immunostimulants in fish culture or in aquaculture of other species for prevention of diseases is a promising new development. In general, immunostimulants comprise a group of biological and synthetic compounds that enhance the non-specific defense mechanisms in animals, thereby imparting generalized protection. This protection may be particularly important for fish that are raised in or released into environments where the nature of pathogen is unknown and immunization by specific vaccine may be futile. Several immunostimulants have been evaluated in fin fishes. Many occasions arise in the course of fish culture that calls for enhancement of immune response. These include strengthening of the normal immune response in order to enhance protection and reduce immunosuppressive conditions. The use of immunostimulants can protect fish from several infectious diseases and decrease mortality rates, however fish cannot be protected against all infectious diseases by immunostimulants. Fish receiving immunostimulants show increased resistance against infection by bacteria such as Vibrio anguillarum, V. salmonicida, Aeromonas salmonicida and Streptococcus sp., viral infections such as IHN (Infectious Hematopoetic Necrosis) and yellow head (YHV) disease, and parasitic infections such as microsporidia (Loma morhua) and Sea-lice. Positive effects of immunostimulants against many bacterial infections such as Cytophaga (Flexibacter) infections have not been reported. Immunostimulants do not increase resistance against Renibacterium salmoninarum, Pseudomonas piscicida or Edward siellaictaluri infection