Effects of dietary Yucca meal on growth,haematology, non‐specific immune responses and disease resistance of juvenile Nile tilapia,Oreochromis niloticus (Linnaeus, 1758)

A 10‐week feeding trial was conducted to determine the effects of dietary yucca meal supplementation on growth, haematology, non‐specific immune responses and disease resistance in juvenile Nile tilapia, Oreochromis niloticus. Six isonitrogenous and isoenergetic experimental diets were formulated to contain 0% (YMS₀), 0.1% (YMS_0.1), 0.3% (YMS_0.3), 0.5% (YMS_0.5), 1% (YMS_1.0) and 2% (YMS_2.0) dietary yucca meal on the dry weight basis. Results of this study showed a higher growth performance for YMS_0.1 group with significant differences with YMS_0.5, YMS_1.0 and YMS_2.0 groups. In addition, whole‐body protein content of fish fed the YMS_0.1 diet was significantly higher as compared to YMS₀. Plasma lysozyme activity significantly increased in YMS_0.1 group comparing to YMS₀ and YMS_0.5 groups. Respiratory burst activity of phagocytic blood cells was significantly enhanced when fish were fed the YMS_0.1 diet. Results also showed that yucca meal supplementation had moderate effects on glutamic oxaloacetic transaminase and cholesterol levels. After the 14‐day challenge test with Aeromonas hydrophila, cumulative survival of fish fed YMS_0.1 diet was significantly higher than that of fish fed diet YMS₀, YMS_1.0 and YMS_2.0. These results suggest that the optimum dietary yucca meal inclusion level in the diet of juvenile Nile tilapia could be between 0.1% and 0.14% (23.9~33.4 mg kg^?1 saponin) as a feed additive to promote growth, enhance the non‐specific immune responses and increase disease resistance.