author(s)
Prasanta Jana, Sutanu Karmakar, Utsa Roy, Mritunjoy Paul, Ashutosh Kumar Singh and Kuntal Krishna Bera

abstract
Use of phytobiotics or herbal extracts for increasing growth and health status is one of the major focuses in fish nutrition research. Intensification of aquaculture causes stress in fishes leading to immunosuppression which ultimately results in reduced growth and diseases. Uses of most antibiotics are banned in aquaculture as they have residual effects and can develop drug-resistant bacterial strain. Hence, stimulation of non-specific immune system is a smart choice available for enhancing the immunity as well as growth performance of cultured species. Phytobiotics are rich in various bioactive compounds that act as immunostimulants. Those compounds mainly enhance the activity of phagocytic cells and increase their bactericidal activities, stimulate the natural killer cells, complement activity, proliferate lymphocytes, lysozyme and antibody responses of fish. Use of diets containing dietary herb or plant extracts to improve growth and disease resistance in fish and shrimp are generally based upon tradition and folklore transferred through generations without knowing any biochemical properties. However, phytobiotics are a new frontier area of aquaculture and there is an underlying need to obtain a clear and direct dose-dependent stimulatory effect upon the growth, immune status and physiology of fish.