Nothobranchius fuscotaeniatus Seegers, 1997

Nothobranchius fuscotaeniatus Seegers, 1997 View in CoL

( Figs. 7A–B View FIGURE 7 )

Material examined. RMCA 1997.082 View Materials .P.0032-0033, 1 male, 36.2 mm SL, 1 female, 24.2 mm SL; Tanzania: Rufiji drainage, Kitonga; 08°03.13’ S, 39°00.53’ E; B. Watters, R. Wildekamp, B. Cooper; 31 May 1997; field code: TAN 97-9 GoogleMaps .

Additional material examined. 2 males, 35.1–43.4 mm SL, 1 female 25.9 mm SL; Tanzania: Rufiji drainage, Kitonga; 08°03.13’ S, 39°00.53’ E; B. Watters, R. Wildekamp, B. Cooper; 31 May 1997; field code: TAN 97-9 GoogleMaps .

Diagnosis. Nothobranchius fuscotaeniatus is here assigned to the N. lourensi species group of the subgenus Aphyobranchius by presenting the following combination of characters in males, compared to those of other subgenera: anal fin trapezoidal in shape with a concave lower margin (vs. rounded with convex lower margin); caudal fin rounded with 2–3 central rays slightly elongated forming a mild central lobe (vs. central lobe absent); spawning behaviour in mid-water levels (vs. spawning directly into the substrate), and molecular phylogenetic relationships. Nothobranchius fuscotaeniatus is further distinguished from all the other members of the genus Nothobranchius by the unique diagnostic characters of male colouration comprising a green-blue body with 10–12 distinct red-brown crossbars on entire trunk that extend into dorsal and anal fins; anal and dorsal fins green-blue with crossbars extending from trunk into the proximal and medial parts and with broad black distal band; caudal fin with slender yellow to yellow-green medial band and broad black distal band; as well as female colouration with a unique pattern of light blue and red-brown crossbars on the body and a light blue iridescence on the dorsal and anal fins.

Description. General body features illustrated by Figures 7A–B View FIGURE 7 . Morphometric and meristic characters of examined material are summarized in Table 7.

Male: Medium-sized Nothobranchius species, maximum recorded size 43.4 mm SL. General body shape robust, laterally compressed and deep. Greatest body depth at vertical passing through pelvic-fin origin, 32.5–35.3 % 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 146–153 % of its depth. Anus situated directly in front of anal-fin origin.

Head moderately long (30.4–33.6 % SL), laterally compressed, deeper than wide (head width 64–69 % 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 large, eye diameter 33–36 % HL, positioned entirely in anterior half of head (snout to eye end length 47–50 % HL). Branchiostegal membrane projecting posteriorly from opercle.

Dorsal-fin origin at same vertical positioning as anal-fin origin (mean predorsal length 100–101 in % of preanal length), both fins originating slightly posterior to mid-length of body (predorsal length 53.0–55.5 % SL; preanal length 52.3–55.5 % SL). Dorsal fin with 15–16 rays, extremity rounded. Anal fin trapezoidal in shape, with 17–18 rays; lower margin moderately concave in profile. 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 16–18 branched rays, plus 3–4 dorsal and ventral procurrent rays; central 2–3 rays of fin relatively slightly elongated resulting in mild central lobe.

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 25–26 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 View FIGURE 3 ), 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: Smaller than male, maximum recorded size 25.9 mm SL. Branchiostegal membrane not projecting posteriorly from opercle. Dorsal and caudal fins rounded. Anal fin subtriangular, tip rounded, central rays longer and more rigid. Dorsal fin positioned more posteriorly than in males (predorsal length 61.8–66.1 % SL vs 53.0–55.5). Anal fin positioned more posteriorly than in males (preanal length 62.2–66.9 % SL vs. 52.3–55.5), and base length smaller than in males (18.5–21.9 % SL vs. 24.3–26.7). Head width larger than in males (59–63 % HL vs. 55–58) whereas head depth smaller than in males (80–81 % HL vs. 85–86).

Colouration. Live male ( Fig. 7A View FIGURE 7 ): The body has a series of as many as 12 prominent dark red-brown crossbars resulting from broad scale margins. Scales in the relatively wider intervening sections are a brilliant iridescent blue to blue-green with very narrow dark red-brown edgings. The snout is blue-green to yellow with irregular dark markings including some on the lips. The throat and operculum are yellow to blue-green. The exposed part of the branchiostegal membrane is yellow with black edging. Scales on the dorsum anterior to the dorsal fin may have medium brown centres forming a vague stripe between the dorsal fin and snout. The barred colour pattern of the trunk extends onto the abdomen with intervening scales grading into light green, with only vague dark edgings, that may extend posteriorly to the caudal fin base. The iris is blue-green. The dorsal fin background colour is blue-green in the basal and proximal zones grading to yellow-green through the medial zone; the background is overlaid by irregular dark red-brown to black spots and short crude bars that appear as extensions of the dark bars on the body, becoming broken up and smaller outwards; the distal zone comprises a black marginal band with very narrow light blue to blue-green edging. The anal fin is somewhat similar in colour pattern to the dorsal fin; the basal zone is blue grading to blue-green in the proximal zone through to yellow-green in the medial zone. The basal, proximal and submedial zones are overlaid by dark red-brown to black irregular markings that represent extensions of the dark bars on the body; these irregular markings usually do not extend into outer part of the medial zone but, when they do, they appear broken and sparse; the distal zone comprises a broad black marginal band with very narrow light blue to blue-green edging that is less well developed than in the dorsal fin and may only be present on the very short fin-ray extensions. The caudal fin displays a prominent concentrically-banded pattern; the basal zone is blue-green followed by a narrow arc-like dark red-brown to black band in the proximal zone, followed by a yellow-green band and another, broader, black band and then a yellow to yellow-green band; the distal zone comprises a broad black band. Pelvic fins are blue-green with a black marginal zone. Pectoral fins are hyaline with, in some specimens, very poorly developed and usually only partial, light blue margins.

Live female ( Fig. 7B View FIGURE 7 ): The body has up to 10 narrow cross-bars formed by very dark red-brown or black scale margins. These are similar to those shown by the male but are less well defined in the female and more distinct anteriorly. Scales in the intervening parts of the body have iridescent light blue to blue-green centres and yellow-brown scale margins. Scales on the dorsum are yellow-brown. The head is yellow-brown with some irregular dark red-brown to black markings; the throat is pale yellow-brown. The lower part of the operculum is yellow and there is a patch immediately posterior to the operculum that has broad bright yellow scale margins. Scales on the abdomen are light yellow-brown, some showing iridescent light blue centres and bright yellow margins. The dorsal and anal fins have yellow-brown fin rays with the intervening membrane being iridescent blue-green; the distal component is grey; some dark spots are sparsely present over most of the fins and those at or near the fin bases show a crude extensional arrangement with the bars on the body. The caudal, pectoral and pelvic fins are hyaline. The iris is golden grading outwards to blue-green.

Distribution. Nothobranchius fuscotaeniatus is known from a single site only, comprising an originally thickly vegetated ditch on the immediate west side of a now defunct road, about 2 km southwards from the south bank terminus for the old ferry across the Rufiji River ( Fig. 1 View FIGURE 1 ). It is, therefore, within the lower Rufiji River drainage. Since the original discovery of this species by the first author and colleagues in May, 1997, and also soon after by Seegers (1997), numerous visits to that site have been unable to find it there again.

Conservation status. Nothobranchius fuscotaeniatus is listed as Critically Endangered B2ab(iii) ( Nagy & Watters 2019e). The species is currently known only from the type locality with an area of occupancy (AOO) of 4 km 2. Several surveys in the years following the original discovery were unable to detect its presence at either the type locality or elsewhere in the drainage of the Rufiji River, whereas other congeners were found in abundance at the type locality and in the general area. As shown in Nagy & Watters (2021) and Figure 7D View FIGURE 7 herein, the type locality has been significantly modified since the species was first discovered in 1997. Extensive local farming around the type locality represents increasing pressure on land resources that has resulted in habitat degradation in the area. The species is adapted to specific habitat conditions by occupying a niche among the densely vegetated marginal zones of the pool and is likely, therefore, to be very highly susceptible to habitat modifications by agriculture, which invariably results in habitats becoming more open.