The standard length is 5.5- 10.0 times of body height, 3.3-5.5 times of head length, 4.4-5. 1 times of tail stalk length and 9.0- 13.5 times of tail stalk height. The head length is 2. 1-4.6 times of the kiss length, 4.0-7.8 times of the eye diameter and 3.2-4.1times of the eye spacing. The length of the tail handle is 2.0-2.6 times the height of the tail handle. Long body, flat head, and gradually flat body after dorsal fin. Kiss the flat circle. The mouth is inferior and the mouth is wide. The upper jaw is slightly longer than the lower jaw, and the upper jaw, lower jaw and palatal bone all have villous fine teeth. The lip is thick, the upper and lower lips are combined at the mouth corner, and the posterior groove of the lip is discontinuous. Must be 4 pairs, all longer. The end of maxillary whisker exceeds pectoral fin. The lateral chin must reach the base of pectoral fin. The eyes are the same size, located on the back of the head, and the width between the eyes is flat. The nostrils are separated, and the posterior nostril is farther away from the front edge than the anterior nostril. The branchial foramen is large, and the left and right branchial membranes are combined but not connected with the isthmus. The dorsal fin spines are weak, and the trailing edge is smooth and serrated. Thoracic fin spines are developed, longer than dorsal fin spines, and the leading edge has small serrations. The trailing edge is coarsely serrated. The ventral fin is fan-shaped, and the end is far less than the starting point of the anal fin. Lipid fin is very long, about 3 times as long as the base of gluteal fin, its starting point is close to dorsal fin, and its end is not free, and the joint with the base of caudal fin is notched. The caudal fin is concave and the upper leaf is slightly longer than the lower leaf. The anus is near the base of the ventral fin, but far from the starting point of the anal fin. The body is bare and scaleless. The lateral line is straight. The body side is gray-black, and the body color is darker above the lateral line. The abdomen is white. Some individuals have dark brown spots on their sides. Dactylis japonicus is a common primary ornamental fish of Dactylis japonicus.