Nomorhamphus lanceolatus can be distinguished from all congeners by the combination of the following characters: lower jaw short; no fleshy lower jaw appendage in males; presence of black pigmentation in anal and dorsal fin; life coloration with yellow and orange colored anal, dorsal, and caudal fin, ventral surface of lower jaw orange and yellow belly; a lanceolate, dorsally slightly curved spiculus in the male andropodium, with the middle segments of the spiculus in contact with the distal tip of the third anal-fin ray; nine to ten segments proximal to spinae (mode nine segments); segments three or four to six or seven (mode four to seven) of second anal-fin ray in males with a dorsal and a ventral row of 'subsegments' forming small squares and rectangles of different sizes, so that these segments seem to be subdivided; third anal-fin ray slightly constricted longitudinally, giving the appearance of two distinct rays, distal part of this ray is slightly curved ventrally to contact spiculus (Ref. 97329).