Diagnosed from all congeners except Tetragonopterus anostomus by the number of gill rakers on the upper and lower limbs of the first gill arch (18-20/10-12 vs. 12-14/8-10, respectively). Differs from T. anostomus byhaving terminal position of the mouth (vs. subsuperior). Can be futher distinguished from T. anostomus and T. denticulatus in the number of principal teeth in the dentary (four vs. five or six) and also by having relatively robust teeth with blunted cusps (vs. relatively smaller teeth with somewhat sharper cusps); from T. argenteus by the number of predorsal scales (7-9 vs. 12-16); from T. carvalhoi by having a rounded spot on the caudal peduncle (v. a lozenge-shaped spot); and from T. rarus by the lack of dark stripes on the lateral surface of the body (vs. the presence of such stripes) (Ref. 93280).

Description: Dorsal-fin rays ii,9; anal-fin rays v, 32-35; pectoral fin with i,12-14; pelvic-fin rays i, 7; scales in longitudinal series 30-33; and scale rows between lateral line and pelvic-fin origin 3·5 (Ref. 93280).