Diagnosis: Nothobranchius attenboroughi belongs to the N. ugandensis species group presenting the following combination of characters in males: body colouration light blue with red or red-brown scale margins; frontal part of head red-brown, throat light blue or red; caudal fin uniform red; and anal fin light blue or yellow with red-brown spotted pattern (Ref. 123150). Nothobranchius attenboroughi differs from all other members of the N. ugandensis species group by a light blue anal fin with red-brown dots proximally and medially; becoming yellow distally with red-brown narrow stripes parallel to fin rays; and caudal peduncle length 122-129% of its depth vs. 96-121% or 130-157% (Ref. 123150). Furthermore, it differs from N. moameensis, by a smaller body depth, 25.7-31.0% of standard length vs. 31.6-33.2%; a smaller head depth, 80.1-86.2% of head length vs. 87.1-94.3%; and a dorsal fin that is positioned posterior to anal fin, preanal length mean 59.8% of standard length and predorsal length mean 60.6% of standard length vs. anteriorly positioned with mean values of 62.2% and 60.9% respectively, in N. moameensis (Ref. 123150).

Description: Medium size Nothobranchius species; general body shape robust, laterally compressed and moderately deep; greatest body depth at vertical in front of pelvic-fin origin, 25.7-31.0% of standard length; greatest body width at pectoral-fin base with body progressively narrowing towards caudal-fin base (Ref. 123150). Dorsal profile slightly concave from tip of snout to nape and convex from nape 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 moderately deep, length 122-129% of its depth; anus situated directly in front of anal-fin origin (Ref. 123150). Head moderately long, 26.7-32.2% of standard length, laterally compressed, deeper than wide, head width 73-78% 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 to centre of eye; premaxilla and dentary with many irregularly distributed conical teeth on inner rows and slightly curved teeth on outer row; eye diameter 27-32% of head length, mainly in anterior half of head, snout to eye end length 47-53% of head length; branchiostegal membrane projecting posteriorly from opercle (Ref. 123150). Dorsal-fin origin posterior to anal-fin origin, both fins originating posterior to mid-length of body, predorsal length 59.1-63.1% of standard length and preanal length 57.9-61.5% of standard length; 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; dorsal fin with 14-17 rays; anal fin with 16-17 rays; pectoral fin subtriangular, insertion slightly posterior to margin of opercular opening, base slightly oblique, upper fin rays positioned slightly anteriorly to lower fin rays, its tip reaching or slightly overlapping base of pelvic fin; pelvic fin subabdominal, origin at about mid-length of body, short, base medially separated, its tip reaching urogenital papilla; caudal fin subtruncate, with 20-22 branched rays, plus 2 or 3 dorsal and ventral procurrent rays (Ref. 123150). Scales cycloid, body and head entirely scaled, except for ventral surface of head; no scales on base of dorsal and anal fins; scales in mid-longitudinal series 28-32 plus two or three small scales on caudal fin base; transverse rows of scales in front of dorsal-fin origin 11-12; scale rows around caudal peduncle 12-14 (Ref. 123150). Cephalic squamation pattern variable; frontal neuromasts separate in two rows of shallow grooves behind the upper lip, with one neuromast in each groove; cephalic sensory system at supraorbital level fragmented in two discontinuous shallow grooves with two exposed neuromasts in each, whereas at supratemporal level with three or four exposed neuromasts in undivided, slightly curved shallow groove; preorbital canal in deep groove with two or three exposed neuromasts; infraorbital level with series of about 12 small buttons at ventral and posterior margin of orbit; postorbital canal in deep groove with two or three exposed neuromasts; preopercular system with exposed neuromasts in deep groove on preopercular portion, whereas in shallow groove with exposed neuromasts and small buttons on ventral portion; mandibular canal in shallow groove with about six small neuromasts; one neuromast on each scale along trunk mid-longitudinal series (Ref. 123150).

Colouration: Colouration of live male: scales on trunk and head light iridescent blue with red-brown margins, forming a reticulation pattern and irregular oblique bars anterodorsally on trunk; scales on abdomen faint blue with less pronounced margins; frontal portions of head red-brown; lips light blue; throat light blue; posterior scale margins on post-orbital portion of opercle forming two to three red-brown oblique bars; iris golden; exposed branchiostegal membrane light blue; dorsal-fin base light blue, almost completely covered by a pattern of irregular red-brown patches proximally and wide red-brown stripes parallel to fin rays medially, for some specimens gradually turning into light blue distally; anal fin light blue with irregular red-brown dots proximally and medially, becoming yellow distally with red-brown narrow stripes parallel to fin rays; caudal fin uniform red; pelvic fin light blue proximally, with yellow with red-brown dots in medial and distal zones; pectoral fin hyaline with narrow light blue distal margin (Ref. 123150). Colouration of live female: trunk and head light grey-brown, darker on dorsum and lighter ventrally; scales with a very narrow grey margin; scale centres iridescent silver to very pale blue; all fins hyaline; iris golden (Ref. 123150).