Diagnosis: Nothobranchius serengetiensis is distinguished from all other members of the Nothobranchius neumanni species group by the following combination of characters: in the male, a relatively straight dorsal profile and a marked angular transition between the head and body, which is concave in older males; the anal fin has two horizontal red bands of variable width that are, less commonly, irregular in shape; usually, a yellow or white band, also of variable width, separates the red bands; the proximal part of the fin is light blue-gray and the margin is white to blue; the caudal fin is red, less commonly with a dark red or black margin and, occasionally, with a narrow blue, gray or yellow submargin (Ref. 98818).

Description: Nothobranchius serengetiensis is a Nothobranchius species of relatively large size with a pointed snout, slightly upward-directed subterminal mouth, and a slightly protruding lower jaw (Ref. 98818). The head profile is slightly concave with a distinct transition to the dorsal profile; the dorsal profile is slightly convex to almost straight from the nape to the dorsal fin base; the caudal peduncle profile is slightly convex at the upper and lower sides (Ref. 98818). The dorsal fin rays number 14-18, the anal fin rays 14-18, 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 median longitudinal line number 29-35, plus 2-4 on caudal fin base, most with a shallow pit in the center and one neuromast; the transverse row of scales above the pelvic fins numbers 14-15, and the scale count around the caudal peduncle is 16-17 (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 gray-blue, the abdomen pale gray, the back brown-red; the posterior margins of the scales are red to red-brown, forming a reticulated pattern; the snout and lower lip are red to red-brown, the throat is pale blue-gray; the projecting part of the branchiostegal membrane is light gray with red markings and a white margin; the dorsal fin is blue-gray with irregular dark red spots and stripes that increase in frequency and size proximally; the caudal fin is red with a narrow dark red or black margin, and a narrow discontinuous light gray or blue to pale yellow submarginal band may also be present; the basal part of the anal fin is light blue to gray, usually plain but with sparse red spots in some populations; this basal component of the anal fin is most commonly followed distally by a narrow red band, a narrow pale yellow, cream-coloured or white band, a second, relatively broad red band and a blue margin of variable width; in some populations the cream-coloured or white band is very broad and the outer part of the fin is of the same colour, rather than blue; in rare cases the light coloured band separating the two red bands is absent and the outer part of the anal fin comprises a narrow submarginal blue band followed by a grey marginal zone; the pelvic fins are similar to the anal fin; pectoral fins are hyaline with pale blue to white 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).