This species is distinguished from its congeners by the shape of the andropodium in males: sickle-shape spiculus is curved dorsally, the proximal and middle segments in contact with the distal tip of the third anal-fin ray; the spiculus' distal segments are curved ventrally, no contact to third anal-fin ray; in males, the second anal-fin ray with 3 or 4 segments proximal to paired spines, third or fourth segment with a dorsal and a ventral row of 'subsegments' forming squares and rectangles of different sizes, the third or fourth segment appears to be subdivided into two separate rays, from the half of its length up to the spines, with a varying number of subsegments (?5 subsegments per row); first segment of the first anal-fin ray slightly constricted longitudinally, giving the appearance of 2 distinct rays; third anal-fin ray composed of 2 elongate segments, each approximately half the length of the entire ray, followed by a few short segments at the distal tip, which contact the spiculus; the fourth anal-fin ray divided into 3 rows from approximately the third of its length, forming a kind of a covering for the third anal fin ray with one dorsal and two lateral rows beneath (Ref. 91778). Nomorhamphus rex have a relatively longer lower jaw, LJLB 5.7-11.3 times in SL vs. 13.4-15.9 in N. ebrardtii and 8.8-22.2 in N. kolonodalensis (Ref. 44897).