Diagnosis: Nothobranchius sainthousei is distinguished from the other Nothobranchius species from the drainages of the Upper Congo in northern Zambia and Katanga province of DRC, except N. rosenstocki, by having broad orange-brown posterior scale margins on the trunk, vs. red, and an anal fin with orange-brown margin, vs. light blue or yellow or red-brown or black (Ref. 116789). It is distinguished from N. rosenstocki by having dorsal and anal fins with orange-brown spots, vs. irregular orange-brown bars; furthermore, N. sainthousei is distinguished from all members of the N. brieni group by head length, 25.1-29.3% of standard length vs. 29.6-38.7%, and head width, 71-79% of head length vs. 52-62% (Ref. 116789).

Description: General body shape robust, laterally compressed and deep; maximum observed length in males 40.8 mm standard length; greatest body depth at vertical in front of pelvic-fin origin; 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, straight to slightly concave on caudal peduncle; ventral profile convex from lower jaw to base of last anal-fin ray, straight to slightly concave on caudal peduncle; caudal peduncle shallow, depth 1.4-1.5 times in its length (Ref. 116789). Head short, laterally compressed, deeper than wide; 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 to centre of eye; premaxilla and dentary with many irregularly distributed conical, slightly curved teeth at outer row of lower and upper jaws; orbit large, in anterior half of head, pupil round; branchiostegal membrane projecting posteriorly from opercle (Ref. 116789). Dorsal-fin origin anterior to anal-fin origin, both fins originating posterior to mid-length of body; extremity 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 in some specimens; dorsal fin 15-19 rays; anal fin 15-17 rays; pectoral fin sub-triangular, 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 overlapping base of pelvic fin; pelvic fin subabdominal, origin at about mid-length of body, short, bases medially separated, tip reaching urogenital papilla; caudal fin rounded (Ref. 116789). Scales cycloid, body and head entirely scaled, except for ventral surface of head; scales in mid-longitudinal series 28-31 plus 2-3 small scales on caudal-fin base; transverse rows of scales in front of dorsal-fin origin 10-11; scale rows around caudal peduncle 10-12 (Ref. 116789). Cephalic squamation pattern variable, holotype with E-type, and with E-scales and F-scales overlapping each other at median lateral margin; nostril in front of eye, with single oblique aperture; anterior neuromasts separate in two grooves; cephalic sensory system at preorbital level in a continuous shallow groove, with four exposed neuromasts, whereas at supraorbital level in a curved groove, with four exposed neuromasts; one neuromast on each scale along trunk mid-longitudinal series (Ref. 116789). Total number of vertebrae 29 (Ref. 116789).

Colouration: Live male: scales on trunk and head light blue with broad orange-brown posterior margin, forming irregular reticulated pattern on body; scales on abdomen light blue to silver, with narrow orange-brown margin; snout, frontal and dorsal portions of head orange, throat blue; exposed part of branchiostegal membrane orange; iris golden to green, with dark grey vertical bar through the centre of eye; dorsal fin light blue with irregular orange-brown spots, more distinct at base of fin and merging into striped pattern toward distal edge, parallel to fin rays, with black markings between the first and second and second and third fin rays at anterior margin; anal fin light blue with irregular orange-brown spots, forming short stripes at base of fin, denser at distal part and merged into plain orange-brown margin; caudal fin orange-brown with faint orange-brown spots proximally and a faint light blue, irregular narrow distal margin; pelvic fin orange-brown with faint blue spots; pectoral fin pale hyaline, faint orange at base, with light blue posterior margin (Ref. 116789). Live female: scales on trunk and head pale grey-brown, darker on dorsum and lighter to silver on venter; dark grey reticulation on dorsal and posteroventral portions of flank; blue iridescence on trunk and opercular region; iris golden; all fins hyaline (Ref. 116789).