Diagnosis: Nothobranchius usanguensis is distinguished from all other members of the Nothobranchius neumanni species group by the following combination of characters: in the male, the dorsal profile is convex with almost no transition between the head and body; the anal fin is yellow with a dark red marbled pattern, a distinct dark red, or less commonly black, margin and a light blue-gray proximal part; the caudal fin is red or partially red with a darker red or red-gray terminal band that may be preceded by a narrow relatively light red band (Ref. 98818).

Description: Nothobranchius usanguensis is a Nothobranchius species of relatively large size with a rounded snout and a subterminal mouth that is directed slightly upward (Ref. 98818). The head profile is slightly concave with almost no transition to the dorsal profile; the dorsal profile is convex from the nape to the dorsal fin base; the caudal peduncle profile is straight at the upper and lower sides (Ref. 98818). The dorsal fin rays number 14-17, the anal fin rays 14-17, and the relative position of the base of the first anal fin ray is under the base of dorsal fin ray 1 or 2; the pelvic fins are short, not reaching the first anal fin ray; the pectoral fins reach the first pelvic fin ray (Ref. 98818). Scales on the median longitudinal line number 28-33, plus 1-2 on the caudal fin base, most with a shallow pit in the center and one neuromast; the transverse row of scales above the pelvic fin number 13-14, and the scale count around the caudal peduncle is 16 (Ref. 98818). The supra-orbital squamation is variable, but most specimens have G-type, the anterior part being partly covered with epidermal tissue; the central supra-orbital neuromast systems are in two distinct shallow grooves, both sides of each lined with three shallow lobes; the posterior cephalic neuromast systems are in two curved pits (Ref. 98818).

Colouration: Live males: the body is light blue-gray, the abdomen white to pale gray, and the back is gray-brown; the posterior margins of the scales are gray, forming a reticulated pattern; the throat is pale blue-gray; the projecting part of the branchiostegal membrane is light gray with a white margin; the caudal fin is red with a narrow darker red margin, and a very narrow light gray to pale yellow submarginal band may also be present; the dorsal fin is blue-gray with irregular dark gray-brown to dark gray stripes and spots which become denser and smaller distally; the proximal part of the anal fin is pale blue-gray to yellow-gray, the distal two-thirds is yellow or yellow-white with an irregular, crudely banded pattern of dark red spots and stripes, and dark red margin; an intermittent blue submarginal colouration may also be present; the pelvic fins are similar to the anal fin; the pectoral fins are hyaline with pale white-blue posterior margins; the iris is silver (Ref. 98818). Live females: the body colour is pale olive-gray, being darker on the back and lighter on the abdomen; scales on the back and upper parts of the sides have reflective light blue centers; paired and unpaired fins are colourless; the iris is silver (Ref. 98818).