Fish models of intestinal inflammation are still fairly scarce though dozens of such models have been established in other animals.In this study, we aimed to develop a TNBS-induced enteritis model in grass carp.To induce the intestinal inflammation, 0.25 mL TNBS/ethanol solution(at a concentration of 2.5% TNBS in 50% ethanol) was instilled into the intestine of each fish(70±5 g) via the anus at a water temperature of 28°C.An equal volume of 0.7% physiological saline was instilled as control.After TNBS enema, the intestinal inflammation was assessed by examining the degree of body injury, and the intestinal histopathological characteristics, and by analyzing myeloperoxidase(MPO) activities and gene expression patterns of inflammatory cytokines, IL-1β, IL-8 and TNF-α, in different intestinal segments.The pathological results indicated that all fish survived during the whole observation period following TNBS treatment, and one day after TNBS enema, serious congestion and fester in intestinal mucosa were observed, and abundant inflammatory cells infiltrated into intestinal tissues.On the third day, severe abdominal dropsy occurred, large amounts of inflammatory cells were recruited at the damaged site, and healing of intestinal ulcers appeared.On the seventh day, the number of inflammatory cells decreased gradually, while that of goblet cells increased.Afterwards the abdominal dropsy reduced, the goblet cells densely arranged in the intestinal mucus layer.On the twenty-first day after TNBS enema, the fish recovered nearly into normal conditions, and only a few inflammatory cells could be found.In addition, our results showed that TNBS administration induced similar changes in MPO activities between different intestinal segments.MPO activities in the intestine remarkably increased after TNBS treatment, peaked on the first day.Subsequently, the activities decreased rapidly.On the seventh day, there was no significant difference between the TNBS-induced and the control groups.This pattern in MPO activity appeared to be consistent with those results obtained from the histopathological observations.Moreover, we also found that, after TNBS enema, the mRNA expression patterns of inflammatory cytokine genes, IL-1β, IL-8 and TNF-α, showed roughly the same trend as those of MPO activities.Our results also showed that different intestinal segments exhibited significant differences in inflammatory response, and TNBS induced more severe inflammatory signs in the 3^rd and 4^th segments than the 1^st and 2^nd ones.Overall, these results suggest that we have developed a reliable and reproducible TNBS-induced enteritis model in grass carp.This grass carp model will not only extend our understanding in pathological mechanisms involved in intestinal inflammation of teleost fish, but also provide a tool to screen novel drugs for the treatment of inflammatory diseases in grass carp and other aquacultural animals.