Impact of plant products on innate and adaptive immune system of cultured finfish and shellfish

Aquaculture is one of the fastest growing food-producing sectors around the world. Among various kinds of cultivated organisms many marine and freshwater finfish and shellfish species constitute an important industry with their production increasing every year. Recently due to intensive farming practices infectious diseases pose a major problem in aquaculture industry, causing heavy loss to farmers. A number of approaches have been made to control diseases including sanitary prophylaxis, disinfection, and chemotherapy with particular emphasis on the use of antibiotics. However, the application of antibiotics and chemicals in culture is often expensive and undesirable since it leads to antibiotic and chemical resistance and consumer reluctance. Therefore immunostimulants such as glucan, chitin, lactoferrin, levamisole, and some medicinal plant extracts or products have been used to control fish and shellfish diseases. In this regard the medicinal plant extracts and their products act as immunostimulants modulating the immune response to prevent and control fish and shellfish diseases. The immunostimulants mainly facilitate the function of phagocytic cells, increase their bactericidal activities, and stimulate the natural killer cells, complement, lysozyme activity, and antibody responses in fish and shellfish which confer enhanced protection from infectious diseases. Currently increased consumer demand for perfection in fish and shellfish farms has put new dimensions to the quality, safety, elimination of concomitant pollutants, antibiotics, and carcinogens during the production process. In this context plants or their byproducts are preferred since they contain several phenolic, polyphenolic, alkaloid, quinone, terpenoid, lectine, and polypeptide compounds many of which have been shown to be very effective alternatives to antibiotics, chemicals, vaccines, and other synthetic compounds. In aquaculture the herbal medicines are also known to exhibit anti-microbial activity, facilitate growth, and maturation of cultured species; besides under intensive farming the anti-stress characteristics of herbs will be of immense use without posing any environmental hazard. Administration of herbal extracts or their products at various concentrations through oral (diet) or injection route enhance the innate and adaptive immune response of different freshwater and marine fish and shellfish against bacterial, viral, and parasitic diseases. Even an overdose of immunostimulants may induce immunosuppression without side effects but helps to reduce the losses caused by disease in aquaculture. The present review describes the role of medicinal herbs and their products on innate and adaptive immune response of finfish and shellfish.