Indian Journal of Experimental Biology Vol. 44, September 2006, pp 726-732 Immunostimulatory effect of Tinospora cordifolia Miers leaf extract in Oreochromis mossambicus D Samuel Sudhakaran 1 , P Srirekha 1 , L D Devasree 2 , S Premsingh 3 & R Dinakaran Michael 4 * 1 Nagarjuna Fertilizers and Chemicals Limited, ICICI Knowledge Park, Hyderabad 500 078, India 2 Department of Biotechnology, Sourashtra College, Madurai 625 004, India 3 P.G. Department of Chemistry, The American College, Madurai 625 002, India, 4 Centre for Fish Immunology, P.G. and Research Department of Zoology, Lady Doak College, Madurai 625 002, India Received 17 March 2005; revised 5 May 2006 Immunostimulatory effect of leaf extract of T. cordifolia on (i) specific immunity (antibody response), (ii) non-specific immunity (neutrophil activity) and (iii) disease resistance against Aeromonas hydrophila was investigated in O. mossambicus. Ethanol and petroleum ether extracts of the leaves were used. Both ethanol and petroleum ether extracts administered at doses of 0.8, 8 or 80 mg/kg body weight, prolonged the peak primary antibody titres upto one to three weeks. Ethanol extract at the dose of 8 mg/kg and petroleum ether extract at the doses of 0.8 or 8 mg/kg enhanced the sec- ondary antibody response. All the doses of ethanol extract significantly enhanced neutrophil activity. Fish injected with pe- troleum ether or ethanol extract at a dose of 8 mg/kg were protected against experimental infection with virulent A. hydrophila. The results indicates the potential of T. cordifolia leaf extracts for use as an immunoprophylactic to prevent diseases in finfish aquaculture. Keywords: Immunostimulants, Oreochromis mossambicus, Tilapia, Tinospora cordifolia Fish culture is an age-old practice in India, which is the second largest culture fish producer in the world 1 . One of the major bacterial fish pathogens in India is Aeromonas hydrophila which causes a variety of dis- eases such as haemorrhagic septicaemia, infectious dropsy, tropical ulcerative disease and finrot leading to heavy mortality in aquaculture farms 2-4 . Fish dis- eases can be controlled with the help of antibiotics and other drugs. However, the emergence of antibiotic resistant microorganisms is an important obstacle to their extensive use. Recently the use of immunostimu- lants was introduced as a prophylactic measure 5,6 . An immunostimulant is a substance that elevates non- specific defense mechanisms and specific immune response if the treatment is followed by vaccination or infection 5 . So far, a number of immunostimulants that include a very heterogeneous group of substances like levamisole, lipopolysaccharides, glucans, pepti- doglycans, and muramyl dipeptide have been tested in a variety of fish species 5,7 . Though many synthetic and natural substances have been tested for their immunostimulating abilities, traditional medicinal herbs seem to have the potential to be a rich source of active substances for immunomodulation 8,9 . Indian medicinal plants are a rich source of substances that are claimed to induce paraimmunity, the nonspecific immunomodulation of granulocytes, macrophages, natural killer cells and complement functions in mammalian models. Indian medicinal plants that have immunomodulatory properties have been reviewed in mammalian models 10 . Indian medicinal plants with antioxidant and immunomodulatory activities have been identified and their antioxidant and immunomodulatory effects in mammalian species reviewed 11 . Traditional use of medicinal herbs in India and China to control fish diseases has been reviewed 3,12,13 . Immunostimulatory properties of the leaf extracts of Ocimum sanctum 14,15 and Azadirachtin, a seed kernel compound in Azadirachta indica 16,17 have been re- ported in the tilapia, Oreochromis mossambicus. The immunomodulatory effects of plant products in mammals 18 and fish 19-25 have also been extensively reviewed. —————— *Correspondent author Tel: +91-452-2530527 Fax +91-452-2521333 E-mail: rdmichael2000@yahoo.co.in