Carbonic anhydrase (CA) family is discovered in various species including mammals, avians and even plants, but it is rarely reported in fishes. Ten Pond Loaches were used in this study. The results indicated that no evidence of distribution of CA in esophagus. Nonetheless CA was found in the mucosal epithelium of stomach and in the villous epithelium of intestine demonstrated histochemically by the numerous black sedimentation of cobaltous sulfide (CoS) in these areas. In addition, black sedimentations of CoS were also found in all the vascular endothelium examined and red blood cells of digestive tract. The distribution of CA in Pond loach was more closely resemble amphibians than to other species, suggesting evolutional adaptation for Pond loach in aquatic environments.