Diagnosis: The color pattern of males of Nothobranchius cardinalis and N. rubripinnis have some features that are quite similar: red snout; red pectoral, anal, and caudal fins; and narrow black marginal band to the caudal fin (Ref. 74420). There are, however, some consistent differences: the anal fin of N. rubripinnis has a blue-green background color with red rays and red spots that form irregular transverse bands, especially apparent in the outer, posterior part of the fin, while the anal fin of N. cardinalis is almost a solid red; the pectoral and ventral fins of N. cardinalis are a solid red, whereas in N. rubripinnis these fins are not as intensely coloured and have a translucent quality; the background iridescent blue-green body colour of N. rubripinnis is dominant and the red scale margins are relatively narrow, while in N. cardinalis the red scale margins are much wider, resulting, in some specimens in a dominantly red body; N. rubripinnis always shows a strongly developed, rearward-pointing, chevron pattern on the posterior part of the body, due to the arrangement and slightly increased width of the red scale margins, while in N. cardinalis it is very weakly developed and barely discernible (Ref. 74420). The principal difference in colour pattern of the females of N. cardinalis and N. rubripinnis is the strong and consistent presence of a rearward-pointing chevron pattern on the rear part of the body of N. rubripinnis, which is most strongly developed on the caudal peduncle and is due to enhanced, dark gray scale margins; on females of N. cardinalis the scale margins on the rear part of the body are pale gray and narrow, and may, in some specimens only, form an almost indiscernible chevron pattern on the caudal peduncle (Ref. 74420). The principal differences in colour pattern of males of N. annectens when compared to N. cardinalis are: the main body colour of N. annectens is iridescent blue with golden yellow scale margins; in the rear half of the body there is a strongly developed rearward-pointing chevron pattern caused by red scale margins to every second to fourth row of scales, while the scale margins on N. cardinalis are red, wide, and uniform across the body and, if a chevron pattern is present at all, it is barely discernible; the caudal fin of N. annectens is red with a broad black, vertical, marginal bar, quite different to the relative narrow marginal band shown by N. cardinalis; the pectoral ad ventral fins of N. annectens are pale yellow, whereas on N. cardinalis they are a bright solid red; the anal fin of N. annectens is pale blue, grading out into pale yellow in some populations, while the anal fin of N. cardinalis is almost completely red (Ref. 74420). In contrast to both N. cardinalis and N. rubripinnis, N. annectens lacks the light blue or white margin to the dorsal fin; in N. annectens the dorsal fin margin, if present at all, is always red (Ref. 74420). Although there is some small overlap in the ranges of some characters, males of N. cardinalis differ morphologically from those of N. rubripinnis by: a lesser snout length, 7.1-7.6% of standard length vs. 8.0-9.4%; a lesser snout to eye end length, 17.3% of standard length vs. 17.6-18.9%; a lesser head length, 28.6-32.4% of standard length vs. 31.4-38.3%; a lesser caudal peduncle depth, 13.1-14.3% of standard length vs. 14.2-15.4%; a lesser caudal peduncle length, 19.8-22.9% of standard length vs. 23.1-25.7%; a greater body width, 17.3-19.5% of standard length vs. 12.9-16.7%; a lesser body depth, 30.1-31.6% of standard length vs. 31.1-35.8%; and a greater body length, 67.5-71.4% of standard length vs. 63.5-68.6% (Ref. 74420). Morphological characteristics of the female of N. cardinalis compared to those of N. rubripinnis are less distinctive: a greater body width, 18.7% of standard length vs. 13.2-18.8%; a lesser interorbital width, 7.7% of standard length vs. 8.3-13.5%; a shorter snout to eye end length, 16.4% of standard length vs. 16.5-17.4%; a lesser caudal peduncle depth, 10.8% of standard length vs. 11.6-13.2%; and a shorter anal fin base, 12.6% of standard length vs. 14.1-15.1% (Ref. 74420). The males of N. cardinalis differ in morphology from those of N. annectens by: a greater body width, 17.3% of standard length vs. 14.1-15.0%; a lesser predorsal length, 55.3-57.9% of standard length vs. 56.0-66.7%; a lesser preanal length, 58.2-60.5% of standard length vs. 59.2-66.9%; a lesser number of anal fin rays, 13-14 vs. 15-16; a greater number of scales on the side of the body at the ventral fin position, 12 vs. 11; and a greater number of scales around the caudal peduncle, 16 vs. 14 (Ref. 74420). The morphological characteristics of the female of N. cardinalis compared to those of N. annectens are more distinctive than for the male: a greater body length, 69.0% of standard length vs. 65.3%; a lesser body depth, 28.3% of standard length vs. 28.5-32.3%; a lesser interorbital width, 7.7% of standard length vs. 11.1-12.7%; a lesser snout length, 5.1% of standard length vs. 5.7-7.9%; a greater preanal length, 67.0% of standard length vs. 59.6-67.3%; a greater prepelvic length, 53.7% of standard length vs. 46.8-53.1%; a lesser caudal peduncle depth, 10.8% of standard length vs. 12.1-14.4%; and a lesser number of anal fins rays, 14 vs. 15-16 (Ref. 74420).

Description: Males with body laterally compressed and relatively deep (Ref. 74420). Snout rounded, mouth terminal, directed upward (Ref. 74420). Dorsal profile slightly curved (Ref. 74420). Dorsal fin origin anterior to the anal fin origin and behind the mid-length of the body; dorsal fin 15 rays; anal fin 13-14 rays; unpaired fins rounded; dorsal and anal fin ray tips project only very slightly from the membrane, both fins covered with epidermal tissue; small contact organs in the form of papillae on the dorsal and anal fins (Ref. 74420). Scales on mid-longitudinal series 26 plus 3 on caudal fin base; transverse rows of scales above pelvic fin 12; scale rows around caudal peduncle 16; ctenii on the scales on the posterior half of the body; three rows of scales behind the eye; supra-orbital squamation in a G-type pattern; frontal part of supra-orbital squamation partly covered with epidermal tissue (Ref. 74420). The branchiostegal membrane projects slightly from the operculum; distal end wrinkled (Ref. 74420).

Colouration: Body and head scales of male are iridescent light blue with distinct red margins which are widest on the operculum; the red scale margins form a strong reticulated pattern; scales on the frontal parts of the back are iridescent golden green with less distinct red margins; the colour of the scale centers is iridescent blue, grading to pink on the abdomen, although still with distinct red margins; on the caudal peduncle of some specimens the reticulation on the body forms a barely discernible rearward-pointing chevron pattern; the snout, throat, and projecting part of the branchiostegal membrane are deep red, the latter with a white edging (Ref. 74420). The background colour of the basal parts of the dorsal fin is bright blue-green, grading outwards to golden green, with a transition into a narrow submarginal zone of darker green to black, followed by a narrow pale blue or white margin; fin rays in the dorsal fin are red and most prominent in the frontal half of the fin; red spots are present in the outer and posterior parts of the dorsal fin and these merge to form irregular transverse bands, most prominent in the posterior part of the fin; the anal fin displays a narrow light blue zone at the base grading outward to a solid red; rays in the basal zone are also red and there is a small but prominent blue-green patch on the posterior, basal part of the fin; the caudal fin is solid red except for a narrow, black marginal band; pelvic fins are solid red; pectoral fins are solid red except for a discontinuous, narrow light blue edge in some specimens (Ref. 74420). The iris is a reflective blue-green (Ref. 74420). The background body colour of females is light gray-brown, darker on the back, grading to white or pink on the abdomen; scale centers have small, iridescent pale blue patches, most prominent on the gill covers and the mid-section of the body; the branchiostegal membrane projects only slightly from the gill cover; scale margins are a gray-brown and narrow, producing a vague reticulated pattern that is most obviously developed on the caudal peduncle (Ref. 74420). The dorsal and anal fins are translucent; the caudal fin is hyaline (Ref. 74420). The iris is silver (Ref. 74420).