Effect of Excoecaria agallocha on non-specific immune responses and disease resistance of Oreochromis niloticus against Streptococcus agalactiae

The current study was designed to evaluate the effects of Excoecaria agallocha leaf extracts on immune mechanisms and resistance of tilapia, Oreochromis niloticus, after challenge with Streptococcus agalactiae. Fish were divided into 6 groups; groups 1-5 fed with E. agallocha leaf extracts at 10, 20, 30, 40 and 50 mg kg− 1 level, respectively. Group 6 were fed without extract addition and acted as control. E. agallocha extracts were administered as feed supplement in fish diet for 28 days and the hematological, immunological, and growth performance studies were conducted. Fish were infected with S. agalactiae at a dose of 15 × 105 CFU mL− 1 and the total white blood cell (WBC), phagocytosis and respiratory burst activities of leukocytes, serum bactericidal activity, lysozyme, total protein, albumin, and globulin levels were monitored and mortalities recorded for 15 days post infection. Results revealed that feeding O. niloticus with 50 mg kg− 1 of E. agallocha enhanced WBC, phagocytic, respiratory burst, serum bactericidal and lysozyme activities on day 28 pre-challenge and on 3rd, 6th, 9th, 12th and 15th day post-challenge as compared to control. Total protein and albumin were not enhanced by E. agallocha diet. E. agallocha increased the survival of fish after challenge with S. agalactiae. The highest mortality rate (97%) was observed in control fish and the lowest mortality (27%) was observed with group fed with 50 mg kg− 1 extract. The results indicate that dietary intake of E. agallocha methanolic leaf extract in O. niloticus enhances the non-specific immunity and disease resistance against S. agalactiae pathogen.