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The efficacy of supplementing diets with ethanolic extracts from three medicinal plants (Arabic gum; Acacia arabica, Water lily; Nymphaea lotus, Iron weed; Vernonia ambigua) on the innate immune response and diseases resistance in Heterobranchus longifilis challenged with Pseudomonas aeruginosa were studied. H. longifilis juvenilles (20.4 ±3.8g) were fed diets containing 0% (control diet C), 1.5% extracts of; Acacia Arabica (diet 1), Nymphea lotus(diet2) and Vernonia ambigua (diet 3) 100g-1 of feed at 5% biomass daily and the innate immune response parameters were examined after the end of the experimental period (42days). The blood leukocyte phagocytic activity was enhanced in fishes fed diet 2 and diet 3 from the 14th day while those fed diet 1 showed no significant(P>0.05) increase until the 28th day. Serum lysozyme activities were stimulated in fish fed diet 2 from the 14th day while significant increase were recorded from the 28th day in those fed diet 1 and diet 3. Significantly (P<0.05) increased leukocytes respiratory burst activity were only observed from the 42nd day in all the experimental diets but there was no significant change (P>0.05) in any of these parameters in the control group. A challenge test with virulent strain of Pseudomonas aeruginosa following 42days of feeding showed 100% mortality in the bacterial infected H. longifilis in the control group by the 15th day, while mortalities recorded for the fishes fed the diet supplemented groups; diet 1, diet 2 and diet 3 were 52% (relative percent survival (RPS) 48%), 44% (RPS=56%) and 68% (RPS=32%) respectively at the end of the challenge experiment (24days). The cumulative mortality index for the control group was 130.8 which was equated to 1%, while the lowest mortality of 0.26% was obtained in the D3 diet fed group and were significantly different (P<0.05) in all the treatment groups. These results suggests that the dietary inclusion of these plants extracts may elevate the innate immune response and enhanced disease resistance in H. longifilis.
Keywords: Heterobranchus longifilis, innate immune response, plant extract, Pseudomonas aeruginosa.