clarius fuscus dorsal fin rays 55-67; ​​anal fin rays I-43-51; pectoral fin rays I-6-9; pelvic fin rays I-5. Gill rakers 15-18. Free vertebrae 53-61.
The body length of clarius fuscus is 5.3-5.9 times the body height, 4.3-6.1 times the head length, and 2.8-3.5 times the front back length. The head length is 2.3 to 3.6 times the length of the snout, 7.2 to 11.4 times the diameter of the eye, and 1.6 to 2.1 times the distance between the eyes.

The body is elongated, the origin of the dorsal fin gradually flattened forward, and gradually flattened later. The head is flat and broad, wedge-shaped. There are bony plates on the top and sides of the head, covered by skin, and the upper occipital spine is far behind the origin of the dorsal fin. The snout is broad and blunt. Mouth large, subordinate, arcuate. The upper jaw slightly protrudes from the lower jaw, and there is a rupture in the center of the mandibular dentition. Eyes small, laterally superior, located in the anterior quarter of the head. Eyes are wide and flat. The anterior and posterior nostrils of clarius fuscus are far apart, and the anterior nostrils are short tubular; the posterior nostrils are round holes, located in front of the eyes. The nose whiskers are located at the front edge of the posterior nostrils, and the ends extend back slightly beyond the gill openings; the jaw whiskers are close to or beyond the origin of the pectoral fins; the lateral chin whiskers are slightly longer than the medial chin whiskers, and none of them reach the origin of the pectoral fins. Gill openings large. The opercular membrane is not connected to the isthmus. Gill rakers elongated.
The dorsal fin base is long, without bony spines, the fin rays are hidden in the epidermis, the starting point is about the vertical above the rear end of the pectoral fin, and the distance from the snout is smaller than the distance from the caudal fin base. The anal fin base is longer, shorter than the dorsal fin base, and the distance from the origin to the caudal fin base is greater than to the rear end of the pectoral fin base. The pectoral fins are small, laterally inferior, the front edge of the spines is rough, the rear edge is weakly serrated, and the end of the fin rays extends backwards up to the vertical below the origin of the dorsal fin. The pelvic fins are small, the origin is located vertically below the origin of the dorsal fin, the rear end of the pectoral fin base is greater than the origin of the anal fin, and the end reaches or extends beyond the origin of the anal fin. The anus is closer to the origin of the anal fin than to the rear end of the base of the pelvic fin. The caudal fin is not connected to the dorsal and anal fins, and is round.
The living body of clarius fuscus is generally brownish-yellow, and some individuals have a brownish-black back and a light belly. There are some small irregular white spots on the side of the body.