This species can be distinguished from all Sundaic congeners (except for G. decussatus) in having brown or brownish gray body with prominent dark vertical bars at the level of the adipose-fin base and the base of the caudal fin (vs. without distinct vertical markings on body). It differs from G. decussatus in lacking (vs. having) anteromedial striae in the thoracic adhesive apparatus and the pelvic fins not reaching (vs. reaching) the base of the first anal-fin ray when adpressed. G. pictus further distinguishes from Sundaic congeners by the following unique set of characters: absence of anteromedial striae in thoracic adhesive apparatus; pectoral-fin spine length 17.3-22.9% SL; dorsal-fin spine length 15.4-20.9% SL; margin of dorsal fin concave; straight dorsoposterior margin of adipose fin; caudal peduncle depth 8.4-10.9% SL; absence of prominent dark longitudinal stripes running through each lobe in caudal fin; and absence of prominent pale midlateral stripe on body (Ref. 128699).