Effect of Withania somnifera (L. Dunal) root as a feed additive on immunological parameters and disease resistance to Aeromonas hydrophila in Labeo rohita (Hamilton) fingerlings
Introduction
The use of antibiotics and chemotherapeutics for prophylaxis and treatment in intensive aquaculture has been widely criticized for its negative impact [1]. Problems including solubility, palatability, toxicity, cost, delivery, and governmental restrictions have limited the available antibiotics to a select few, especially in food fish culture. Further the traditional application of antibiotics and chemotherapy has been characterized by partial success in the management of diseases like motile aeromonad septicaemia (MAS) and aeromonad-associated diseases like epizootic ulcerative syndrome (EUS). A good example of disease resistance was observed in Cyprinus carpio [2] the isolates of Aeromonas hydrophila from the skin, organs and intestinal tract were resistant to 50 mg l−1 Ampicillin, 30 mg l−1 Teramycin, and 20 mg l−1 chlorotetracycline. Enhancement of the immune system seems to be the most promising method of preventing fish diseases. This modulation can be achieved with vaccines, which enhance the acquired (or specific) immune response of the fish and are considered to be the most effective agents, but a single vaccine is effective against only one type of pathogen, and in the case of many pathogens (like the bacterium A. hydrophila) no effective vaccines available due to the complex antigenic structure [3]. Also commercial vaccines are expensive for fish producers and may not be available for all species and against emerging diseases [4]. Fish, like other vertebrates, respond to infectious agents in both nonspecific and specific ways, although they depend to a much greater extent on the nonspecific mechanisms. Immunostimulants of herbal origin have the ability to increase resistance to disease by enhancing nonspecific and specific defence mechanism in fish [5]. The Indian medicinal plant Withania somnifera has been reported to posses several medicinal properties. W. somnifera (L. Dunal) belongs to the family Solanaceae and which is commonly found or scientifically cultivated in Tripura state of the north east region of India. Research reveals W. somnifera possesses anti-inflammatory [6], anti-tumor [7], anti-stress [8], anti-oxidant [9], immunomodulatory [10], hemopoietic [11] and rejuvenating [12] properties. W. somnifera root is used as a Rasayana in the Indian ayurvedic tradition as a dietary supplement promoting rejuvenation, mental and physical health, as well as providing a defence against aging and challenging environmental factors [13]. Studies conducted in fishes with the extract of W. somnifera are scanty and scattered. Feed containing W. somnifera plant extract at the rate of 200 mg kg−1 significantly reduced the mortalities of juvenile greasy grouper (Epinephelus tauvina) against the Vibrio harveyi infection [14]. Post larvae of Penaeus monodon fed with W. somnifera herbal medicinal diets exhibited stress resistance [15].
In this backdrop, it was planned to systematically evaluate the dietary administration of the root of W. Somnifera effect on immunological parameters and disease resistance against A. hydrophila infection of L. rohita fingerlings, which is considered to be the major aqua-crop species contributing about 40% of the total fresh water aquaculture production in India [1]. Hence an approach is made by using an appropriate method of application relevant to farm conditions.
Section snippets
Fish and management
650 nos. of clinically healthy fishes (L. rohita) average weight 18.43 ± 0.5 g and average length of 10.27 ± 0.75 cm were collected from the College Fish Farm and were acclimatized in the laboratory condition in 1000L FRP tanks for 15 days at 27–28 °C before the commencement of the experiment. Fishes were provided with adequate aeration and fed with normal feed (Rice bran and oil cake 1:1) at the rate of 3% of body weight twice a day.
W. somnifera
The plant of W. somnifera was collected from the local farmers of
NBT assay
NBT level in all the groups of fishes fed with diet containing W. somnifera root powder was insignificant on 14th day of sampling. The groups T1 and T2 showed increasing trend from 14th to 42nd days of sampling then decreased notably but were significantly (p < 0.05) higher. T3 groups were insignificant on all the days of sampling in comparison with control (Fig. 1).
Phagocytic activity
Phagocytic activity in T1 and T2 groups of fishes fed with diet containing W. somnifera root powder showed increasing trend from
Discussion
The increasing interest in the use of immunostimulants for boosting the defence mechanisms and protection against diseases in fish is of recent origin. The effect of W. somnifera on the immune systems at various levels in mammalian models is well established and it has been an official drug mentioned in the Indian Pharmacopoeia. The present study on fish L. rohita revealed increase in NBT value in the group T1 and T2 on the 14th to 42nd and than decrease on 56th day post challenge supports the
Acknowledgements
The authors are thankful to Dr. J.R. Dhanze, Dean, College Of Fisheries, Lembucherra for providing all the infrastructure facilities needed for the conduct of the work. Authors also thankful to Dr. Ratan Kumar Saha, Associate Professor and Dr. Anil Datt Upadhyay,Assistant Professor both from College of Fisheries,Tripura for their timely help, guidance and valuable suggestions.
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