C. serralabium can be distinguished from the other species of Callichthys by having the lower lip serrated (it is smooth in all other species). It also has 8–9 branched rays in the pectoral fin (instead of 6–7) and an irregular color pattern of dark, diffuse blotches on flanks of adults.[3] The fish will grow in length up to 15.8 centimetres (6.2 in) SL.[3]
The body is elongated and moderately depressed anteriorly; the trunk and caudal peduncle are progressively more compressed towards the caudal fin. The body profile between snout and dorsal-fin origin straight to slightly convex. The snout is rounded or roughly triangular in dorsal view. The mouth is slightly inferior (pointed downwards).[3]
The dorsal fin and pectoral fins have one spine. The pectoral fin spine has stronger
odontodes anteriorly and small retrorse hooks posteriorly. The pectoral spine of fully developed nuptial males is elongated and thick. The pelvic fins and caudal fin are rounded. The adipose fin has a pointed, depressible spine.[3]
