Diagnosis: Nothobranchius nikiforovi is distinguished from all other congeners, except N. eggersi, by males presenting two phenotypes; the blue phenotype having a bright iridescent light blue to blue-green body, with narrow red-brown scale margins creating irregular reticulated pattern forming chevron-shaped crossbars on posteroventral portion of body and median fins light blue with red-brown dotted pattern; the red phenotype has a dark red head, light blue dorsal and anal fins proximally and medially, dark red distally, with dark red stripes parallel to the fin rays, and plain dark red caudal fin (Ref. 123990). It differs from N. eggersi by male colour pattern: the blue phenotypes having median fins with dark grey distal portion, some of the rays of dorsal and anal fins with white tips only, vs. median fins light blue with distinct slender white distal band; the caudal fin lacking a spotted pattern, vs. dots arranged into irregular curved stripes; the red phenotype has a golden stripe between the nape and dorsal-fin origin, vs. light blue stripe; the dorsal and anal fin distal portion plain red and without light distal band, vs. with distinct narrow white distal band; the pelvic fin without distal band, vs. with distinct slender light blue to white distal band; furthermore, it differs from N. eggersi by the morphometric characters of having greater postorbital length of 49-55% of head length, vs. 42-48%, and greater head width of 64-71% of its depth, vs. 56-62% (Ref. 123990).

Description: Relatively small-sized Nothobranchius species, specimens were observed to attain 30 mm standard length (Ref. 123990). General body shape robust, laterally compressed and deep; greatest body depth at vertical passing through pelvic-fin origin, 25.3-31.6% of standard length; greatest body width at pectoral-fin base with body progressively narrowing towards caudal-fin base; dorsal profile convex from tip of snout to base of last dorsal-fin ray; postdorsal profile slightly concave on caudal peduncle; ventral profile convex from lower jaw to base of last anal-fin ray; postanal profile slightly concave on caudal peduncle from insertion of posteriormost anal-fin ray to caudal-fin base; caudal peduncle deep, length 124-132% of its depth; anus slightly anterior to anal-fin origin (Ref. 123990). Head moderately long, 27.5-32.7% of standard length, laterally compressed, deeper than wide, head width 64-71% of its depth; snout slightly pointed, smaller than eye diameter; mouth supraterminal, slightly oblique in profile; jaws subequal, lower jaw longer than upper, posterior end of rictus at same level or slightly ventral of centre of eye; premaxilla and dentary with many irregularly distributed conical, slightly curved teeth at outer row; orbit large, 33-39% of head length, mainly in anterior half of head, snout to eye end length 45-51% of head length, at median portion of head side; branchiostegal membrane projecting posteriorly from opercle (Ref. 123990). Dorsal-fin origin anterior to anal-fin origin, both fins originating posterior to mid-length of body; distal border of dorsal and anal fins rounded, with small contact organs in form of papillae on fin rays and distal margin with short filamentous rays; posterior extremity of dorsal fin reaching caudal-fin base; dorsal fin with 14-16 rays; anal fin with 13-16 rays; pectoral fin subtriangular; insertion slightly posterior to margin of opercular opening; base slightly oblique, upper fin rays placed slightly anteriorly to lower fin rays, tip reaching or slightly surpassing base of pelvic fin; pelvic fin subabdominal, its origin at about mid-length of body, short, bases medially separated, tip reaching urogenital papilla; caudal fin subtruncate, with 13-14 branched rays, plus two to five procurrent rays at dorsal and ventral origins (Ref. 123990). Scales cycloid, body and head entirely scaled, except for ventral surface of head; no scales on the base of dorsal and anal fins; scales in mid-longitudinal series, 26-28 plus two or three small scales on caudal-fin base; transverse rows of scales in front of dorsal-fin origin 10-11; scale rows around caudal peduncle 12 (Ref. 123990). Frontal squamation pattern variable; anterior nostril at anterior tip of snout, tubular opening lateral to upper lip; posterior nostril in front of orbit, with oblique oval aperture; frontal sensory system with one neuromast in shallow groove; cephalic sensory system at supraorbital level fragmented into two discontinuous portions, with one neuromast at anterior level in shallow groove, continued over orbit at posterior supraorbital level with two exposed neuromasts, whereas at supratemporal level in slightly curved shallow groove, with three or four exposed neuromasts; preorbital canal in shallow groove with three exposed neuromasts; postorbital canal in deep groove with one exposed neuromast; infraorbital level with about dozen small buttons at ventral and posterior margin of orbit; preopercular system with six to seven exposed neuromasts in deep groove on preopercle portion, whereas in shallow groove with small buttons on ventral portion; mandibular canal in shallow groove with about ten small buttons; one neuromast on each scale along trunk mid-longitudinal series (Ref. 123990).

Colouration: Colouration of live males, blue phenotype: scales on trunk bright iridescent blue-green, with narrow red-brown scale margins creating irregular reticulated pattern; scales on abdomen light blue to white; scales on dorsum anterior to dorsal fin golden green; lower jaw, snout, and frontal prtions of head blue-green; posterior scale margins on post-orbital portion of opercle creating three red-brown oblique bars; exposed branchiostegal membrane light blue-green; iris light blue to golden; median fins light blue sparsely spotted with red-brown dots, and with dark grey distal portion, some raysof dorsal and anal fins with white tips; pelvic fin yellow-green; pectoral fin hyaline with light blue tip (Ref. 123990). Colouration of live males, red phenotype: scales on trunk bright iridescent light blue, with narrow dark red scale margins creating intense reticulated pattern, forming chevron-shaped crossbars on posteroventral portion of body; scales on abdomen light blue to silver; dorsum with golden scales on dorsal region, creating stripe between nape and dorsal-fin origin; lower jaw, snout and frontal portions of head dark red; posterior scale margins on post-orbital portion of opercle creating three dark red oblique bars or reticulations; exposed branchiostegal membrane dark red; iris light blue to golden; dorsal and anal fins light blue proximally and medially, with dark red stripes parallel to fin rays, and plain dark red distally; caudal fin plain dark red; pelvic fin plain red; pectoral fin dark red (Ref. 123990). Colouration of live female: scales on trunk and head pale grey-brown, darker on dorsum and lighter to silver on venter; scales with dark grey-brown margin, creating reticulation on trunk; light blue iridescence on trunk and opercular region; iris silver; all fins hyaline (Ref. 123990).