Eutropiichthys cetosus is distinguished from all congeners, with the exception of E. burmannicus by the possession of more rakers 25-35 (vs. 15-20) on the first gill arch. It can be diagnosed from E. burmannicus by having moderately rounded snout in lateral view (vs. distinctly pointed in E. burmannicus) and slightly trilobed in dorsal view (vs. acutely angular in E. burmannicus), a deeper head relative to its length (68.7-77.1% HL vs. 65.4-67.5% HL), fewer branched rays on pectoral fin (13-15 vs. 15-17, rarely 15), and a more slender body (depth at dorsal-fin origin 19.2-23.5% SL vs. 23.7-25.3% SL; depth at anal-fin origin 17.5-23.5% SL vs. 23.2-26.3% SL). It further differs from congeners by the following unique combination of characters: 49-52 total vertebrae, fleshy narial flap not extending medially much past medial margin of naris, mouth rictus reaching vertical through middle of orbit, rough anterior edge of pectoral spine, 43-49 branched anal-fin rays, and caudal peduncle depth 7.8-8.6 % SL (Ref. 96851).