Application of phytochemicals as immunostimulant, antipathogenic and antistress agents in finfish culture

Phytochemicals such as alkaloids, flavonoids, pigments, phenolics, terpenoids, steroids and essential oils are a large group of plant-derived compounds commonly found in diets high in fruits, vegetables, beans and cereals. Plant remedies are closely linked to the maintenance of good health in the cultural heritage of many countries. Despite the potential benefits to health and performance as noted in various terrestrial animals, the use of phytochemicals in fish farming has rarely been investigated. Fish culture is under pressure to decrease the use of synthetic antibiotics and chemotherapeutics because of the risk caused to humans by chemical residues in food and by antibiotic resistance being passed on to human pathogens. Consequently, efforts are being made to exploit plants, plant extracts or natural plant compounds as potential alternatives to synthetic chemicals for the stimulation of immune responses and disease resistance in fish. The phytochemicals contained in herbs may enhance the innate immune system and possess antimicrobial capabilities that may be of immense use in fish culture without causing any environmental and/or hazardous problems. Most phytochemicals are redox active molecules that have anti-oxidant characteristics that may improve the general physiological condition of fish. This review discusses the results emanating from different studies related to the in vivo application of plants and/or phytochemicals in fish in relation to immunostimulation, antipathogenic and antistress activities. Special emphasis is given to the use of Chinese and Indian herbs as immunostimulants in different finfish species during culture and as antibacterial agents against Aeromonas hydrophila.