Diagnosis: Morphology similar to Nothobranchius rachovii and N. krysanovi but distinguished from those by a slightly deeper body in males (Ref. 85866). Nothobranchius pienaari is distinguished from other species of the genus by the following combination og characters: male with colouration consisting of alternating blue-green to grey-green and dark red-brown to almost black scale margins and oblique bars on body and dorsal and anal fins, dark brown spotted basal half of caudal fin, and orange subterminal and black terminal band (Ref. 85866). It can be distinguished from the other species of the subgenus Nothobranchius as follows: from N. furzeri by male colouration and a slightly higher number of dorsal fin rays, 14-16 vs. 14-15; from N. orthonotus by male colouration, lower number of scales on the mid-longitudinal series, 26-31 vs. 28-33; and from N. kadleci by male colouration and shape of the frontal region, higher number of dorsal and anal fin rays, 14-16 vs. 13-14 and 15-17 vs. 13-14 (Ref. 85866). Female distinguished by faint brown oblique bars on posterior part of flanks (Ref. 85866). Nothobranchius pienaari can also be distinguished from N. rachovii and N. krysanovi by a much higher number of diploid chromosomes, 2n=34 vs. 2n=16 for N. rachovii and 2n=18 for N. krysanovi; it can also be distinguished from the karyotypes of N. furzeri and N. orthonotus that both have with 2n=38 a higher number of chromosomes (Ref. 85866).

Description: Robust Nothobranchius species of medium size; snout slightly pointed, mouth terminal, slightly upward directed; body laterally compressed and deep; dorsal profile concave on head and convex from nape to end of dorsal fin, especially in older males; upper and lower profile of caudal peduncle straight (Ref. 85866). Dorsal fin rays 14-16; anal fin rays 15-17; pelvic fins short, not reaching first anal fin ray; pectoral fin reaching past first pelvic fin ray (Ref. 85866). Scales on median longitudinal line 26-31 + 2-3 on caudal fin base, most with shallow pit in centre with one neuromast; transverse row of scales above pelvic fin 11-12; circumpeduncular scales 12-13 (Ref. 85866). Supraorbital squamation G-type; anterior scales partly covered with epidermal tissue; frontal and central supraorbital neuromast systems fused, forming two distinct, shallow grooves, both lined with three shallow lobes on both sides; posterior cephalic neuromast system in two curved grooves (Ref. 85866).

Colouration: Live male: body colour light to dark blue-green to green scale centres; scales with cherry-red to dark red-brown, sometimes almost black margins; these margins form narrow oblique bars, lower end forward; bars on every second row of scales; males of some populations appear very dark to almost black; head grey-brown; abdomen lighter grey-brown to pale pink, back olive-brown; operculum with 3-4 dark red-brown oblique stripes; throat pink to silver-grey depending on population; projecting part of branchiostegal membrane brick-red or red-brown; may have narrow light blue edge; iris bronze or golden with incomplete vertical dark bar; proximal part of caudal fin silver-grey, with bronze sheen in some cases, and small dark brown markings between rays; in some populations these markings can merge and form irregular cross bars; caudal fin margin black with, in most populations, a red to orange submarginal band; width of this band varies between populations from broad to narrow or barely discernable; dorsal fin light blue-grey with bronze hue and numerous dark red-brown or brown spots and stripes which may merge to form irregular bands across the fin rays; submarginal part of dorsal fin green-grey or blue-grey with small dark spots; dorsal fin with narrow white-blue margin; anal fin blue-grey with irregular red-brown spots that may merge to bands; markings are larger in proximal part of fins; submarginal parts darker; may have narrow blue-white margin; ventral fins blue-grey with red-brown markings in basal third; pectoral fins colourless with blue-white margin; iris bronze to golden with dark cross-bar (Ref. 85866). Nothobranchius pienaari is polymorphic in the colouration of its caudal fin; the orange submarginal band ranges from wide and very distinct to almost absent, depending on the population (Ref. 85866). Live female: body colour mainly grey-brown, darker on the back and lighter on abdomen; posterior part of flanks with several darker but faintly developed bars, inclined to the rear; fins colourless; iris bronze or golden with incomplete vertical dark bar (Ref. 85866).