Abstract: In this study, the differences of branchial epithelium of Amur ide (Leuciscus waleckii) originated in Dali Nor Lake (alkal-adapled species) and Songhua River (freshwater species) were observed, which compared under the same bicarbonate stress of 0 (C_A0, pH 7.56), 30 mmol/L (C_A30, pH 9.44) and 50 mmol/L (C_A50, pH 9.55) by histological method. Furthermore, the adaptive relationship between high alkali-tolerance and the micro-adjustment of gill tissue structure was explored. The results showed that the gill structure of the alkaline species changed correspondingly, with the increase of alkalinity, which the gill filament became more full, the gill lamella became longer as well as the interval between lamellae became larger compared to the control (C_A0, P<0.05). The freshwater species also changed, which the gill filament became more full and the interval between lamellae became larger (P<0.05) than the control, although the gill lamella became longer at C_A30 (P<0.05), there was no significant difference between C_A50 and C_A0 (P>0.05). Chloride cells were found in the base of lamellae which increased higher in both of species than that of the control, pavement cells were observed in the secondary gill lamella which became larger and thicker in alkal-adapled species than the control, whereas due to the fusion and cell detachment of pavement cells, pillar cell, and blood cells, the secondary gill lamella of fresh water species was damaged severely. In addition, a large number of mucous cells were found in the epithelium of gill raker of alkal-adapled and freshwater species. With the increase of alkalinity, the mucous cells changed from large and sparse to small and dense. Among them, the mucus cells of alkal-adapled species were more than that of freshwater species, and arranged more orderly and tightly. To sum up, the alkal-adapled species could adapt to the high alkali environment for a long time by keeping the integrity of gill structure and physiological function, while the freshwater species vice versa, because of the loss of physiological function caused by the fusion and exfoliation of gill cells. The results of this study can provide basis and guidance for transplantation and acclimation of freshwater fish in saline and alkaline water in the future.