Nothobranchius lourensi Wildekamp, 1977

Watters, Brian R. & Nagy, Béla, 2025, A review and redefinition of the subgenus Aphyobranchius Wildekamp, 1977, in the seasonal killifish genus Nothobranchius Peters, 1868 (Teleostei: Nothobranchiidae), from ephemeral wetlands of eastern Tanzania, Zootaxa 5570 (3), pp. 401-446 : 418-422

Nothobranchius lourensi Wildekamp, 1977

( Figs. 6A–D )

Material examined. RMCA 77-16 -P-28, holotype, male, 40.6 mm SL; – RMCA 77-16 -P-29-33, 5 males, 39.3 mm SL, 4 females, 30.4–35.4 mm SL; Tanzania: Kwaraza village ; approx. 06°41.9’ S, 38°42.3’ E; R. Wildekamp , T. Steinfort , R. van Haarlem; 12 June 1976; field code: T 76-8 .

Additional material examined. 3 males, 32.5–35.6 mm SL; Tanzania: Kilombero drainage, Ifakara; 08°10.042’ S, 36°41.611’ E; B. Watters, R. Wildekamp, I. Sainthouse; 7 June 1995; field code: TAN 95-4 .

Diagnosis. Nothobranchius lourensi is distinguished from all the other members of the genus Nothobranchius by the unique combination of diagnostic characters of male colouration comprising: blue-green scales with dark brown posterior scale margins, creating a reticulation on the body, with a chevron pattern on the posterior part of trunk; light blue throat; anal and caudal fins with 8–12 distinct narrow to slender bands on the entire fin, perpendicular to fin rays, alternating red-brown and light blue to light yellow, with iridescent light blue to yellow subdistal band and dark grey to black distal band; dorsal-fin anterior half with irregular red brown spots and stripes parallel to fin rays, whereas posterior half with alternating red-brown and light blue to light yellow narrow to slender bands, perpendicular to fin rays; as well as having an anal fin with posterior lower margin straight to mildly concave. Also, the female has a grey-brown body, with a dark grey chevron pattern on the posterior half of trunk.

Description. General body features illustrated by Figures 6A–D . Morphometric and meristic characters of examined material are summarized in Table 6 .

Male: Medium-sized Nothobranchius species, maximum recorded size 40.6 mm SL. General body shape robust, laterally compressed and deep. Greatest body depth at pelvic-fin origin, 28.6–34.0 % SL. Greatest body width at pectoral-fin base with body progressively narrowing towards caudal-fin base. Dorsal profile convex from tip of snout to dorsal-fin origin, 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 deep, length 144–152 % of its depth. Anus situated directly in front of anal-fin origin.

Head moderately long (29.2–32.8 % SL), laterally compressed, deeper than wide (head width 64–70 % of its depth). Snout distinctly 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. Orbit moderately large, eye diameter 27–36 % HL, positioned entirely in anterior half of head (snout to eye end length 45–50 % HL). Branchiostegal membrane projecting posteriorly from opercle.

Dorsal-fin origin at about same vertical positioning as anal-fin origin (mean predorsal length 94–105 as % of preanal length), both fins originating slightly posterior to mid-length of body (predorsal length 52.3–56.2 % SL; preanal length 53.7–57.6 % SL). Dorsal fin with 14–16 rays, extremity rounded. Anal fin anterior margin and anterior part of lower margin rounded, posterior part of lower margin straight to mildly concave, angular to posterior margin, with 17–20 rays. Dorsal and anal fins with short fin-ray extensions. Pectoral fin subtriangular, insertion slightly posterior to margin of opercular opening, base slightly oblique, upper fin rays positioned slightly anterior to lower fin rays, with tip reaching or slightly overlapping base of pelvic fin. Pelvic fin subabdominal, origin at about mid-length of body, short, base medially separated, with tip reaching urogenital papilla. Caudal fin rounded, with 14–18 branched rays, plus 3–4 dorsal and ventral procurrent rays.

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 28–30 plus two or three small scales on caudal-fin base. Transverse rows of scales in front of dorsal-fin origin 10; scale rows around caudal peduncle 12.

Cephalic squamation pattern G-type. Two frontal neuromasts behind upper lip, posterior in shallow groove. Cephalic sensory system at supraorbital level in divided shallow groove with one and three exposed neuromasts, in anterior and posterior portions, respectively ( Fig. 3d ), whereas at supratemporal level with four exposed neuromasts in undivided, slightly curved, shallow groove. Preorbital canal in shallow groove with three exposed neuromasts; infraorbital level with series of about dozen small buttons at ventral and posterior margin of orbit; postorbital canal in deep groove with one exposed neuromast. Preopercular system with seven exposed neuromasts in deep groove. Mandibular canal in shallow groove with three small neuromasts. One neuromast on each scale along trunk mid-longitudinal series.

Female: Slightly smaller than male, maximum recorded size 35.4 mm SL. Branchiostegal membrane not projecting posteriorly from opercle. Dorsal and caudal fins rounded, former with 15–17 rays. Anal fin subtriangular, tip rounded, central rays longer and more rigid. Anal fin positioned more posteriorly than in males (preanal length 61.7–67.1 % SL vs. 53.7–57.6), and base length smaller than in male (18.6–21.4 % SL vs. 23.4–26.7). Head width larger than in males (59–63 % HL vs. 54–59) whereas head depth smaller than in males (79–81 % HL vs. 83–87).

Colouration. Live male ( Figs. 6A–C ): Scales on trunk and head are iridescent blue to blue-green with narrow brown to red-brown margins, forming a regular reticulation pattern with, on the posterior part of the body, a weakly developed diagonally-barred or chevron pattern. Scales on abdomen light blue to white with less pronounced margins that are paler red-brown to yellow-brown in colour. Scales on the dorsum anterior to dorsal fin have broader margins and may have yellow-tinged centres. Snout, frontal and dorsal portions of the head are mainly brown although some populations show red lips; the throat is pale blue to blue-green with a yellow tinge. Operculum has light blue to blue-green scale centres with red-brown margins in the upper part, grading to yellow margins in the lower part. Exposed part of branchiostegal membrane is yellow to white. Iris is blue to blue-green. The dorsal fin background is iridescent yellow-brown to golden colour and, in some populations, may show a red tinge in the basal and proximal zones and some blue green colour in the distal zone. The background is overlaid by dark red-brown to maroon spots that are arranged in such a way as to coalesce in part, forming irregular concentric bands or, in some specimens, lines parallel to the fin rays; the latter linear arrangement is more prominent in the basal and proximal zones but may extend through the medial zone. A narrow dark red to maroon marginal band is invariably present and some specimens also show light blue tips to short fin-ray extensions. The anal fin background comprises a light blue to grey basal zone grading to blue-green, yellow-green or yellow in the remainder of the fin. The background is overlaid by 5–7 dark maroon bands, the most distal of which forms a marginal band. The innermost bands in the proximal and submedial zones may be relatively indistinct and short, where the others are distinct and prominent extending fully across the fin in a pattern ranging from straight to curved, more or less parallel to the distal margin. Background colour of the caudal fin is variable: it can be yellow in the basal, proximal and medial zones grading to a lighter yellow or blue in the subdistal zone; or blue-green or blue in the basal, proximal and medial zones, grading to blue in the subdistal zone; or blue or yellow throughout the basal to subdistal zones. The background is overlaid by 4–5 concentric bars conforming to the general outer shape of the fin comprising, essentially, rows of coalescent dark maroon spots. There is a distinct black marginal band most commonly preceded by a submarginal zone relatively free of maroon markings and which appears as a distinct band showing the background colour. Pelvic fins mimic, in a simpler fashion, the colour pattern of the anal fin with maroon markings, arranged in a crude banding, on a yellow, blue-green or blue background. Pectoral fins are dominantly hyaline with poorly developed, and usually only partial, blue margins.

Live female ( Fig. 6D ): Trunk and head light grey, darker on the dorsum and lighter ventrally. Scales on the flanks have narrow darker grey-brown margins which may form a faint reticulated pattern on the posterior part of the body; scale centres on the trunk above the abdomen are iridescent pale blue; the operculum is iridescent light blue or yellow. All fins hyaline. The iris is pale golden.

Distribution. Nothobranchius lourensi is endemic to seasonal freshwater habitats in coastal Tanzania and is the most widespread member of the Aphyobranchius subgenus, occurring most abundantly in the marginal and peripheral zones of the Kibasira Swamp in the Kilombero River valley but relatively sparsely elsewhere ( Fig. 1 ). The Kilombero system represents a fairly remote component of the Rufiji River system, connected to it through the Ulanga River, the downstream continuation of the Kilombero River. Relatively rare, isolated, single site occurrences have also been reported from: the lower Ruvu River near Kwaraza, representing the type location; a couple of sites in the lower Rufiji River system, one associated with the Ruhoi River and another situated 2 km south of the main course of the Rufiji River near where it approaches the delta; a single occurrence is also known from the Luhule/ Luhute River floodplain within the so-called Mbezi Triangle (sensu Watters et al. 2007; Watters 2009).

Conservation status. Nothobranchius lourensi has been evaluated as Near Threatened ( Nagy & Watters 2019d). The known extent of occurrence (EOO) is 28,006 km ². Within its area of distribution, the occurrence of the species is currently known from more than 10 threat-based locations, with disjunct populations in several river drainages. There is increasing habitat degradation due primarily to expansion of agriculture in the area, including the conversion of some seasonal habitats into permanent ponds (e.g. in the Kwaraza area of the lower Ruvu River system, where the type locality occurs), thereby modifying them in ways that render them unsuitable to support the seasonal life cycle of the species.

Figures

FIGURE 1. Distribution of species belonging to the subgenus Aphyobranchius, all of which occur in the east-central and southern coastal lowlands of Tanzania: N. janpapi (yellow-filled circle), N. luekei (red-filled triangle), N. geminus (orange-filled diamond), N. lourensi (green-filled square), N. fuscotaeniatus (blue-filled inverted triangle), N. cf. janpapi (dark magenta-filled circle). The inset map shows the area of distribution in a somewhat broader geographic context, to include the distribution of N. willerti (red-filled star) in the lower Tana River area of northeastern coastal Kenya, a species that herein is considered to belong to the subgenus Adiniops, rather than Aphyobranchius to which it was ascribed in the original description by Wildekamp (1992). Note that individual symbols on the map may represent more than one locality or population where the sites are close to one another and could not reasonably be resolved at the scale of the map.

FIGURE 3. Cephalic structure: a, Nothobranchius janpapi; b, N. luekei; c, N. geminus; d, N. lourensi and N. fuscotaeniatus. Key to label abbreviations: an, anterior nostril; pn, posterior nostril; f, frontal neuromast; so, supraorbital canal; st, supratemporal canal.

FIGURE 6. Wild-caught specimens of Nothobranchius lourensi and examples of typical habitat. A. N. lourensi Ifakara TAN 95-4, male, Kilombero River drainage; B. N. lourensi Kitonga north TAN 97-9, male, lower Rufiji River drainage; C. N. lourensi TSTS 10-12, male, Kilombero River drainage; D. N. lourensi TSTS 10-12, female, Kilombero River drainage; E. Location Ihango TAN 02-25, a typical thickly vegetated shallow habitat on the floodplain of the Kilombero River, Kibasira Swamp (photograph June 9, 2002), hosting N. lourensi and N. lucius; F. Location Narubungo TAN 02-24, very thickly vegetated residual pool alongside a railway embankment, Kilombero River drainage, Kibasira Swamp (photograph June 9, 2002), hosting N. lourensi, N. geminus, N. kilomberoensis and N. lucius. See also FIGUREs 5C and D, and FIGURE 7C for further examples of seasonal pools that host N. lourensi. Photographs by B.R. Watters (A, B, E, F) and B. Nagy (C, D).