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Dorsal spines (total): 0-0; Dorsal soft rays (total): 15-17; Anal spines: 0-0; Anal soft rays: 15-17; Vertebrae: 27-27. Diagnosis: Nothobranchius derhami belongs to the N. ugandensis species group presenting the following combination of characters in males: body colouration light blue with red to red-brown scale margins; frontal part of headred-brown and throat light blue or red, caudal fin uniform red; anal fin light blue or yellow with red-brown spotted pattern (Ref. 123150). It differs from all members of the N. ugandensis species group by a dorsal fin with a slender light blue subdistal band and a narrow black distal band; an anal fin with broad subdistal zone cream to yellow, with narrow red-brown to black distal band; and a smaller suborbital depth, 16-18% of head length vs. 19-28% (Ref. 123150). Males from Nothobranchius derhami are distinguished from the similar N. ugandensis by lower jaw light blue vs. lower jaw red in red morph or grey brown in yellow morph of N. ugandensis, upper lip and snout red vs. grey brown on yellow morph, the body sides with red irregular vertical stripes vs. without red pattern in yellow morph, by dorsal fin with subdistal blue stripe and broad black rim vs. without defined subdistal stripe and rim, by anal fin with spots vs. without spots or if present reduced to a few dots, and caudal fin plain red vs. yellowish with a black marginal stripe and with or without dark dots in the yellow morph, red anteriorly, orange posteriorly and with a black margin in some of the red morph (Ref. 123202). Males of N. derhami are distinguished from the congener, nearest in distribution, N. robustus, by light blue with posterior margin of the scale red creating a banded pattern on flank vs. intense plain red colouration on whole flank, or at least on posterior half portion, by light blue proximal portion with a pattern of red spots on dorsal, anal and pelvic fin vs. fins completely red (Ref. 123202).
Description: Body relatively deep, compressed; greatest body depth at vertical through pelvic-fin insertion (Ref. 123202). Dorsal profile straight to slightly concave on head and convex from nape to posterior extremity of dorsal fin base, slightly concave on caudal peduncle; ventral profile convex, slightly convex to anal-fin origin, slightly concave on caudal peduncle (Ref. 123202). Head narrow, sub-triangular in lateral view; orbit at anterior half of head, at median portion of head side; snout slightly pointed, mouth supraterminal, slightly oblique in profile; 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, unicuspid, slightly curved teeth of variable size, a small number of larger teeth on the outer rowin both jaws; teeth on middle portion of vomer (Ref. 123202). Gill-rakers on first branchial arch 3+7; six branchiostegal rays; basihyal pentagonal; single antero-dorsal process of urohyal present; branchiostegal membrane projecting posteriorly from opercle in males but not in females (Ref. 123202). Dorsal and anal fins rounded, with small papillate contact organs on fin rays and distal margin with short filamentous rays in males; dorsal fin origin anterior to anal fin origin, anal fin origin at vertical through dorsal fin rays 1-2, tip of dorsal fin reaching middle caudal fin in males; anal fin triangular with rounded tip in females, anal fin origin at vertical through dorsal fin rays 2-3, anal and pelvic fin origin positioned relatively more posteriorly than in males, 59.6-69.8% of standard length vs. 57.0-64.0% and 49.1-56.8% of standard length vs. 45.9-51.3% (Ref. 123202). Pectoral fin subtriangular, insertion slightly posterior to margin of opercular opening, base slightly oblique, tip slightly overlapping pelvic fin base in males, not reaching pelvic fin in females; pelvic fin origin at about mid-length of body, short, bases medially separated, tip reaching urogenital papilla; urogenital papilla short and cylindrical in males, surrounded by an expanded membrane forming a pocket shaped structure overlapping anterior portion of anal fin in females; caudal fin subtruncate (Ref. 123202). Dorsal-fin rays 15-17; anal-fin rays 15-17; caudal-fin rays 29-32; pectoral-fin rays 18-21; pelvic-fin rays 6; second proximal radial of dorsal fin between neural spines of 11th and 12th vertebrae in males; first proximal radial of anal fin between pleural ribs of 8th and 9th vertebrae in males; total vertebrae 27 (Ref. 123202). Scales cycloid, body and head entirely scaled; cephalic squamation pattern irregular, holotype presenting G-type; scales in median lateral series 27-29 + 4 on caudal-fin base; transverse scale rows 10-12; scale rows around caudal peduncle 14-16 (Ref. 123202). One neuromast on each scale of midlateral longitudinal series; some neuromasts above and below medial lateral series, starting at median portion of the trunk; frontal neuromast pattern 'open' type; cephalic sensory system at anterior supraorbital neuromast series with 5 neuromasts; posterior supraorbital neuromasts series curved with 3 neuromasts; cephalic neuromasts, rostal separate in two rows of one neuromast each, supraorbital formula 2+3+3; preopercular neuromast series in an open groove, distal ridge slightly overlapping opercle (Ref. 123202).
Colouration: Colour in life for male: scales on trunk and head light blue to very light greenish with red posterior margin, forming irregular vertical stripes on body, becoming dense and plain red on dorsal portion of the body; scales on abdomen light blue to whitish; dorsal portion of head red, lower jaw light blue to light grey, throat light blue to whitish; posterior scale margins on post-orbital portion of opercle creating three to four red-brown oblique bars; exposed part of branchiostegal membrane whitish; iris with yellowish reflection, a faint black vertical bar through centre of eye; dorsal fin light blue with vermiculate red blotches on sub-proximal portion, red bars following fin rays on middle portion, and subdistal light blue stripe; anal fin light blue on proximal portion, creamy white on distal half, with dense pattern of red dots; margin of dorsal fin black, anal fin margin dark red to grey-black; caudal fin red; pectoral fin hyaline; pelvic fin light blue to whitish with red dots (Ref. 123202). Colour in life for females: body and head scales light brown-grey, whitish ventrally; posterior scale margins darker than remainder, forming a reticulated pattern; opercular region with light blue reflection and scales on middle flank of the body with golden reflection; fins hyaline; iris silvery (Ref. 123202). |