ABSTRACT
The use of immunostimulants in fish diets has accelerated in recent years as more production-grade diets are fortified with a variety of natural sub stances that promise to heighten innate immunity. Promotions on the use of such diets cite increased health and survival of fish fed enhanced diets, com pared to fish fed other production diets, but do not provide documentation of the claims. Laboratory research continues to focus on injection, immersion, intragastric or intestinal administration of immunostimulants, methods that are not practical for large-scale production applications (Raa 1996; Sakai 1999). Investigations of the effects of orally administered immunostimu lants have occurred only in the past decade, and caution must be used in drawing conclusions from the studies. Production level studies have not been conducted, and beyond anecdotal evidence, few published reports sup port claims of uniform benefits from immunostimulants in aquaculture applications. Fish farmers have experienced variable results, although labora tory trials have produced positive immunostimulatory effects at the molecu lar and cellular level. The effects measured in vitro or in vivo in controlled laboratory experiments cannot be assured under less uniform production conditions.
