Diagnosis: caudal peduncle relatively long, with minimal depth as large as horizontal distance between adipose and caudal fin bases, or in a few cases almost twice as large as the horizontal distance between the adipose and caudal fin base (never twice as large); pectoral spine almost completely smooth on its anterior margin; preorbital head length less than maximum head depth; colouration pattern on flanks faint and not clearly demarcated, often with 1 horizontal row of round spots on flanks; adipose fin mostly very well-developed (height 5-8% SL), dorsal fin high (19-30% SL), head deep (head depth 79-97% head width)(Ref. 81642).

Description: body and head relatively elevated, head depth greater than (rarely equal to) preorbital length; barbels relatively short, maxillary barbell at most just reaching pectoral spine base, external mandibular barbel never reaching tip of spine; humeral process of cleithrum (visible through the skin behind the opercle) thin and pointed, with the width of its base shorter than the length of the process; in certain very large specimens this process is robust and more or less triangular; dorsal fin may be very high; in adults, adipose fin relatively solid and high (Ref. 81642).

Coloration: preserved specimens vary from grey to dark brown or almost black; the only marking, not always present, is a horizontal series of 1-6 large black spots, less clearly marked posteriorly on the flanks; ventrum brown or creamy white; occasionally a pale reticulation of the dorsum, adipose and caudal fins is perceptible; other fins always uniformly coloured (Ref. 81642).