The immunomodulatory effects of tuftsin on the non-specific immune system of Indian Major carp, Labeo rohita C.K. Misra a , B.K. Das a, * , S.C. Mukherjee b , P.K. Meher c a Aquatic Animal Health Division, Central Institute of Freshwater Aquaculture, Kausalyaganga, Bhubaneswar-2, Orissa 751 002, India b Fish Pathology Division, Central Institute of Fisheries Education, Fisheries University Road, Seven Bungalows, Versova, Andheri (W), Mumbai 400 061, India c Fish Genetics Division, Central Institute of Freshwater Aquaculture, Kausalyaganga, Bhubaneswar-2, Orissa 751 002, India Received 27 April 2005; revised 15 August 2005; accepted 5 September 2005 Available online 15 November 2005 Abstract The purpose of this study was to determine if injections of different dosages of tuftsin would enhance the immune response and disease resistance against the infections due to the opportunistic pathogens Aeromonas hydrophila and Edwardsiella tarda in Labeo rohita fingerlings. Hence, four different dosages of tuftsin in PBS suspension at the rate of 0, 5, 10, 15 mg kg ÿ1 body weight of fish were injected intraperitoneally to the fingerlings of L. rohita at 2-week intervals for four times. After every 2-week interval, dif- ferent serum biochemical, haematological and immunological parameters of fish were evaluated. Biochemical and haematological parameters including serum total protein content, albumin content, globulin content, albulin:globulin ratio, glucose content, leuco- cyte counts etc.; cellular immune parameters including superoxide anion production, phagocytic activities, lymphokine production index etc.; humoral immune parameters including lysozyme activity, complement activity, serum bactericidal activity etc., in the fish were evaluated after every 2-week interval. After 56 days, fish were divided into two subgroups under each major treatment group for challenge with two pathogens A. hydrophila and E. tarda. The mortality (%) and agglutinating antibody titre was recorded on 28th day post challenge. Most of the immune parameters including leucocyte count, phagocytic ratio, phagocytic index, lyso- zyme activity, complement activity, and serum bactericidal activity were significantly (p % 0.05) maximum on 42 days after three i.p. injections of 10 mg kg ÿ1 body weight of tuftsin. Challenge study indicated least mortality in the group of fish injected with 10 mg kg ÿ1 body weight of tuftsin for four times. Multiple injections of tuftsin might have maintained the activation of phagocytic cells for a long period, which in turn led to long-term protection in the fish. Thus, multiple injections of 10 mg kg ÿ1 body weight of tuftsin for three times can be advocated for enhancing the immune response of fish species under aquaculture. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: Tuftsin; Multiple injections; Immune response; Disease resistance; Labeo rohita Abbreviations: CFU, colony forming units; Con A, concanavalin A; DMSO, dimethyl sulphoxide; FCS, foetal calf serum; i.p., intraperitoneal; KOH, potassium hydroxide; NaCl, sodium chloride; NBT, nitroblue tetrazolium; PBS, phosphate-buffered saline; SAS, statistical analysis system; TSA, tryptic soya agar. * Corresponding author. Tel.: C91 674 465421; fax: C91 674 465407. E-mail addresses: ckmisra5@yahoo.co.in (C.K. Misra), basantadas@yahoo.com (B.K. Das), subhasmukherjee@yahoo.com (S.C. Mukherjee), premmeher@rediffmail.com (P.K. Meher). 1050-4648/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.fsi.2005.09.004 Fish & Shellfish Immunology 20 (2006) 728e738 www.elsevier.com/locate/fsi