Semotilus atromaculatus is distinguished by having the following characters: body barely compressed at front, compressed at caudal peduncle; mouth pointed; 47-65 scales on lateral line; dorsal fin with 8 rays; large black spot at front of dorsal fin base, black caudal spot (not distinct in large individuals); large terminal mouth reaching past front of eye. Coloration consists of gray-brown above, dark stripe along back; herringbone lines on upper side in young; dusky black stripe (darkest on young) along olive-silver side, around snout and onto upper lip; black bar along back of gill cover; and orange at dorsal base, orange lower fins, blue on side of head, pink on lower half of head and body, and 6-12 large tubercles on head in breeding males (Ref. 86798).