Use of bacterial subcellular components as immunostimulants in fish aquaculture

Aquaculture and fisheries products are expected to play a leading part in addressing the food necessities of the increasing human population. However, in intensive aquaculture, fish are exposed to stress conditions that deteriorate their immune systems, leading to increased disease vulnerability. These disease outbreaks have resulted in production losses and represent one of the key constraints in fish farming. Accordingly, aquaculture disease management efforts have concentrated on the establishment of environmental friendly and lasting methods. Recently, several studies have revealed that various bacteria (especially probiotics)-derived cellular components might be used as promising immunostimulants in fish aquaculture. Such components curtail the risk concomitant with the use of antibiotics, chemotherapeutics, vaccines and probiotics. Among the various health advantages ascribed to bacterial cellular components, the modulation of specific and nonspecific immune responses, cytokine gene expression and anti-pathogenic activities are most anticipated benefits. Their potential as vaccine adjuvants for fish culture has also been demonstrated. However, as an emerging practice, limited knowledge is available regarding the detailed interactions with fish immune systems. Therefore, the underlying mechanisms involved in fish immune cell activation need to be explored further. In this context, the present article aspires to review the available studies on the use of bacterial cellular components in fish culture and their biological effects on fish such as growth promotion, immunostimulation and anti-pathogenic activities as well as to evaluate the factors that control the optimal induction of immune responses in fish. In addition, future issues that merit further investigation are suggested.