Nothobranchius cooperi Nagy, Watters & Bellstedt, 2017

Family:  Nothobranchiidae (African rivulines)
Max. size:  2.58 cm SL (male/unsexed)
Environment:  pelagic; freshwater; pH range: 6.18 - 6.35
Distribution:  Africa: upper reaches of Mansa River, tributary of Luapula River, and seasonal Lufimba system, flowing into Lake Bangeulu, in Zambia (Ref. 117281).
Diagnosis:  Dorsal spines (total): 0-0; Dorsal soft rays (total): 14-16; Anal spines: 0-0; Anal soft rays: 14-16; Vertebrae: 26-27. Diagnosis: Nothobranchius cooperi belongs to the Nothobranchius brieni species group (Ref. 117281). With the exception of N. rosenstocki and N. sainthousei, it is distinguished from all other species of that group by having broad orange, vs. red brown, posterior scale margins on the trunk and anal fin, with a uniform orange-red margin, vs. light blue, yellow, red-brown or black margin (Ref. 117281). It is distinguished from N. sainthousei by having an anal fin that is uniform orange-red with an irregular to regular, light blue-green zone close to the base, vs. orange-brown spots and orange-brown margin, and a wider, more prominent light blue marginal band to the caudal fin; head length 32.5-36.2% of standard length vs. 25.1-29.3%; prepectoral length 32.5-36.2% of standard length vs. 25.1-29.4%; and head width 70-77% of its depth vs. 79-86% (Ref. 117281). It is distinguished from N. rosenstocki by having a prepelvic length 48.8-51.9% of standard length vs. 45.1-49.0%; and a head depth 75-77% of head length vs. 78-84% (Ref. 117281). Furthermore, the species is characterised by a caudal peduncle length 1.2-1.3 times its depth, compared to 1.4-1.5 times in N. sainthousei, and 1.6 times in N. rosenstocki (Ref. 117281).

Description: A relatively small Nothobranchius species; general body shape robust, laterally compressed and deep; greatest body depth in front of pelvic fin origin, 27.9-31.4% of standard length; greatest body width at pectoral-fin base with body progressively narrowing towards caudal fin base (Ref. 117281). Dorsal profile convex from tip of snout to base of last dorsal fin ray, straigth 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, length 1.2-1.3 times its depth; anus situated directly in front of anal fin origin (Ref. 117281). Head short, laterally compressed, deeper than wide; head width 70-77% of its depth; snout slightly pointed, about the size of 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 relatively small, 21-25% of head length, in anterior half of head, in dorsal portion of head side; branchiostegal membrane projecting posteriorly from opercle (Ref. 117281). 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; dorsal fin 14-16 rays; anal fin 14-15 rays; dorsal fin origin between neural spines of vertebrae 10 and 12; anal fin origin between pleural ribs of vertebrae 10 and 12; pectoral fin subtriangular, 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 subtruncate, with 14-16 branched rays, plus 3 to 4 unbranched smaller rays at dorsal and ventral origins (Ref. 117281). Scales cycloid, body and head entirely scales, except for ventral surface of head; no scales on dorsal and anal fins; scales in mid-longitudinal series 25-28 plus two or three small scales on caudal-fin base; transverse rows of scales in front of dorsal-fin origin 10-11; scale rows around caudal peduncle 12 (Ref. 117281). Cephalic squamation pattern variable, holotype presenting E-type, with E-scales overlapping each other at median lateral margin (Ref. 117281). Nostril in front of orbit, with single oblique aperture; frontal neuromasts separate in two rows of shallow grooves, one neuromast in each groove; cephalic sensory system at supraorbital level in two discontinuous shallow grooves, with one and two exposed neuromasts, whereas at supratemporal level in a curved groove, with four exposed neuromasts; preorbital canal in shallow groove with three exposed neuromasts; postorbital canal in a very short groove with on exposed neuromast; infra-orbital series with about a dozen neuromasts at ventral and posterior margin of orbit, plus one neuromast just posteriorly from postorbital canal; preopercular canal in an open groove with around a dozen exposed neuromasts; mandibular canal in shallow groove with about ten very small neuromasts; one neuromast on each scale along trunk mid-longitudinal series (Ref. 117281). Total vertebrae 26-27 (Ref. 117281).

Colouration: Colouration of live males: scales on trunk and head light iridescent blue with broad orange-red posterior margins, forming an irregular reticulated and coarse, highly irregular cross-bar pattern; scales on abdomen faint blue to silver, most with narrow orange-red margins; snout, frontal and dorsal portions of head orange-red; throat pale blue to yellow; exposed part of branchiostegal membrane orange to orange-red; iris golden, with a poorly developed black vertical bar through centre of eye; background colour of dorsal fin light blue-green with a golden hue, grading to grey overlain by iridescent blue-green in distal zone; irregular orange-red spots present, larger and more distinct at base of fin, grading into a striped pattern, parallel to fin rays, towards distal edge; some irregular dark grey spots occasionally present in submarginal zone; prominent black markings present on membrane between first 3-4 anterior fin rays; a thin blue margin, usually discontinuous, occasionally present on dorsal fin; whereas in other specimens either absent or very sparsely developed; anal fin fairly uniform orange-red with an irregular to regular, light blue-green zone close to base; some specimens with a second, poorly developed, light blue-green band, usually represented only by a row of spots, extending across central part of anal fin; a very narrow blue edging occasionally present on anal fin; whereas in some populations either absent or very sparsely developed; specimens showing second band and blue edging to anal fin most commonly showing also a blue margin to dorsal fin; base colour of bulk of caudal fin grey with iridescent blue-green on membrane between rays, overlain by orange-red patches concentrated near fin base and extending distally as orange-red streaks; grey base colour of caudal fin intensified in distal parts of fin forming a vague subdistal band, replaced distally by an iridescent blue marginal band; pelvic fins orange-red; pectoral fins dominantly hyaline, with faint orange at base and light blue margins (Ref. 117281). Colouration of live female: scales on trunk and head pale grey-brown, darker on dorsum and lighter to silver on venter; vague reticulation on posteroventral portions of flank, due to some scales having relatively dark grey margins; scales immediately above mid-longitudonal line, over abdominal region, have a blue iridescence, extending across upper part of operculum to eye; iris golden; all fins hyaline (Ref. 117281).

Biology:  It is a micropredator, feeding on small aquatic crustaceans, worms, insect larvae and other zooplankton (Ref. 117281). The species appears to qualify as vulnerable (B1bii) according to IUCN criteria (Ref. 117281).
IUCN Red List Status: Vulnerable (VU); Date assessed: 20 October 2018 (B1ab(iii)) Ref. (130435)
Threat to humans:  harmless


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