Immunostimulants for aquaculture health management

Abstract

The production of fish and shellfish by aquaculture has become the fastest growing animal food sector in the world. The advances in culture techniques and the introduction of new species have contributed to the rapid growth of the aquaculture industry. The practice of intensification has become common in both finfish and shellfish culture to optimize the returns. High stocking densities, artificial feeding and fertilization have become common husbandry practices in both carp and shrimp culture systems. Due to intensification of culture practices, various diseases of microbial etiology have surfaced in rearing and grow out ponds, being a major threat to the sustainability of the aquaculture industry. Use of synthetic chemicals and antibiotics to prevent or treat various diseases has achieved some success. However, the use of antibiotic therapy in aquaculture inevitably leads to the emergence of resistance in the target bacteria. Vaccination is a useful prophylaxis for infectious diseases of fish, but the development of vaccines against intracellular pathogens has not so far been successful. An alternative approach has been the application of various compounds to boost or stimulate the innate immune system of farmed fish and shrimp. These compounds, termed Immunostimulants are considered an attractive and promising agent for the prevention of diseases in fish and shellfish. Immunostimulants comprise a group of biological and synthetic compounds that enhance the innate or non-specific cellular and humoral defence mechanism. Immunostimulants mainly facilitate the function of phagocytic cells and increase their bactericidal activities. Several immunostimulants also stimulate lysosomes and the antibody responses of fish.