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We conducted this study to determine the chronic effects of Azadirachtin on growth parameters, survival and gill morphology of grass carp [Ctenopharyngodon idella (C. idella)] with an average weight of 11.09±2.3g. We equally distributed 120 fish between three treatments and a control group, with three replicates each. Sublethal concentrations of poison, 0.073 (10% LC50), 0.15 (20% LC50), 0.22 ppm (30% LC50) were selected. Fish were exposed to these doses for 28 days. Increasing doses of Azadirachtin did not affect growth parameters and survival (P>0.05). During the test, we observed fish behavior patterns of irregular swimming, rotation, reaction increased response versus stimulus exterior, solitary and imbalance, histology, epithelial uplifting (swelling), hyperplasia, fusion of gill lamellae and necrosis of gill epithelial cells. The results showed that although the sublethal dose of Azadirachtin over a short time did not affect growth and survival of C. idella but brought about abnormal behavior in fish. There was increased gill tissue destruction with increased poison levels which showed that it could be effective on long duration of exposure.