Nothobranchius nikiforovi, Nagy & Watters & Raspopova, 2021

Nagy, Béla, Watters, Brian R. & Raspopova, Alexandra A., 2021, Nothobranchius nikiforovi, a new species of seasonal killifish from the lower Matandu drainage in south-eastern coastal Tanzania (Cyprinodontiformes Nothobranchiidae), Zootaxa 4950 (1), pp. 103-122 : 113-117

Nothobranchius nikiforovi , new species

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Figure 4

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Nothobranchius cf. eggersi: van der Merwe et al. 2020: 11 .

Holotype. MRAC 2021.001 .P.0001, male, 24.4 mm SL; Tanzania: lower Matandu drainage: Zinga system: ephemeral pool, about 9 km southeast of Njinjo township, 08°51’09” S, 38°57’14” E; A. Nikiforov, V. Korolev, S. Streltsov & S. Torgashev, 14 June 2017.

Paratypes. MRAC 2021.001 .P.0002-4, 3, 2 males, 19.8–20.1 mm SL & female, 14.9 mm SL; collected with the holotype .— MRAC 2021.001 .P.0005-6, 2, male, 24.5 mm SL & female 24.3 mm SL; Tanzania: lower Matandu drainage: Zinga system: ephemeral swamp, about 32 km southwest of Njinjo township, 09°02’38” S, 38°46’23” E; collectors and date as for holotype .

Diagnosis. Nothobranchius nikiforovi is distinguished from all other congeners, except N. eggersi , by males presenting two phenotypes; the blue phenotype having a bright iridescent light blue to blue-green body, with narrow red-brown scale margins creating irregular reticulated pattern forming chevron-shaped crossbars on posteroventral portion of body and median fins light blue with red-brown dotted pattern; the red phenotype has a dark red head, light blue dorsal and anal fins proximally and medially, dark red distally, with dark red stripes parallel to the fin rays, and plain dark red caudal fin.

Nothobranchius nikiforovi differs from N. eggersi by male colour pattern: the blue phenotypes having median fins with dark grey distal portion, some of the rays of dorsal and anal fins with white tips only (vs. median fins light blue with distinct slender white distal band), the caudal fin lacking a spotted pattern (vs. dots arranged into irregular curved stripes); the red phenotype has a golden stripe between the nape and dorsal-fin origin (vs. light blue stripe), the dorsal and anal fin distal portion plain red and without light distal band (vs. with distinct narrow white distal band), the pelvic fin without distal band (vs. with distinct slender light blue to white distal band). Furthermore, it differs from N. eggersi by the morphometric characters of having greater postorbital length of 49–55 % HL (vs. 42–48), and greater head width of 64–71 in % of its depth (vs. 56–62).

Description. General body features of males illustrated by Figure 4 A–C . Morphometric and meristic characters of holotype and paratypes summarised in Table 2. Relatively small-sized Nothobranchius species, maximum observed length of specimens examined 24.5 mm SL, although specimens were observed to attain 30 mm SL. General body shape robust, laterally compressed and deep. Greatest body depth at vertical passing through pelvic-fin origin: 25.3–31.6 % SL. Greatest body width at pectoral-fin base with body progressively narrowing towards caudal-fin base. Dorsal profile convex from tip of snout to base of last dorsal-fin ray; postdorsal profile slightly concave on caudal peduncle. Ventral profile convex from lower jaw to base of last anal-fin ray; postanal profile slightly concave on caudal peduncle from insertion of posteriormost anal-fin ray to caudal-fin base. Caudal peduncle deep, length 124–132 in % of its depth. Anus slightly anterior to anal-fin origin.

Head moderately long (27.5–32.7 % SL), laterally compressed, deeper than wide (head width 64–71 in % 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, slightly curved teeth at outer row. Orbit large (33–39 % HL), mainly in anterior half of head (snout to eye end length 45–51 % HL), at median portion of head side. Branchiostegal membrane projecting posteriorly from opercle.

Dorsal-fin origin anterior to anal-fin origin, both fins originating posterior to mid-length of body. Distal border 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; anal fin, 13–16. 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 surpassing base of pelvic fin. Pelvic fin subabdominal, its origin at about mid-length of body, short, bases medially separated, tip reaching urogenital papilla. Caudal fin subtruncate, with 13–14 branched rays, plus two to five procurrent rays at dorsal and ventral origins.

Scales cycloid, body and head entirely scaled, except for ventral surface of head. No scales on the base of dorsal and anal fins. Scales in mid-longitudinal series, 26–28 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.

Frontal squamation pattern variable. Anterior nostril at anterior tip of snout, tubular opening lateral to upper lip. Posterior nostril in front of orbit, with oblique oval aperture. Frontal sensory system with one neuromast in shallow groove. Cephalic sensory system at supraorbital level fragmented into two discontinuous portions, with one neuromast at anterior level in shallow groove, continued over orbit at posterior supraorbital level with two exposed neuromasts, whereas at supratemporal level in slightly curved shallow groove, with three or four exposed neuromasts. Preorbital canal in shallow groove with three exposed neuromasts; postorbital canal in deep groove with one exposed neuromast; infraorbital level with about dozen small buttons at ventral and posterior margin of orbit. Preopercular system with six to seven exposed neuromasts in deep groove on preopercle portion, whereas in shallow groove with small buttons on ventral portion. Mandibular canal in shallow groove with about ten small buttons. One neuromast on each scale along trunk mid-longitudinal series.

Females slightly smaller than males, maximum observed size 24.3 mm SL. Body more laterally compressed than in males (head width 46–49 % HL vs. 53–58, head width 56–62 in % of its depth vs. 64–71). Branchiostegal membrane not projecting posteriorly from opercle. Dorsal and caudal fins rounded. Anal fin subtriangular, tip rounded, central rays longer and more rigid. Dorsal, anal and pelvic fins positioned more posteriorly than in male (predorsal length 62.6–64.4 % SL vs. 58.1–61.6, preanal length 63.8–65.8 % SL vs. 61.1–62.7, prepelvic length 53.5–56.4 % SL vs. 46.3–51.8, respectively). Base length of dorsal and anal fins smaller than in male (dorsal-fin base length 20.1–22.2 % SL vs. 23.8–26.8, anal-fin base length 16.5–16.8 % SL vs. 20.4–23.9, respectively). No papillae or epidermal tissue present on dorsal and anal fins. Pelvic fin short, tip reaching anus. Caudal peduncle less deep than in male (caudal peduncle length 156–157 in % of its depth vs. 124–132, caudal peduncle depth 12.1–12.3 % SL vs. 12.4–15.2).

Colouration. Live males ( Fig. 4 B–C ) presenting both blue and red phenotypes.

Blue phenotype: Scales on trunk bright iridescent blue-green, with narrow red-brown scale margins creating irregular reticulated pattern. Scales on abdomen light blue to white. Scales on dorsum anterior to dorsal fin golden green. Lower jaw, snout, and frontal portions of head blue-green. Posterior scale margins on post-orbital portion of opercle creating three red-brown oblique bars. Exposed branchiostegal membrane light blue-green. Iris light blue to golden. Median fins light blue sparsely spotted with red-brown dots, and with dark grey distal portion, some rays of dorsal and anal fins with white tips. Pelvic fin yellow-green. Pectoral fin hyaline with light blue tip.

Red phenotype: Scales on trunk bright iridescent light blue, with narrow dark red scale margins creating intense reticulated pattern, forming chevron-shaped crossbars on posteroventral portion of body. Scales on abdomen light blue to silver. Dorsum with golden scales on dorsal region, creating stripe between nape and dorsal-fin origin. Lower jaw, snout and frontal portions of head dark red. Posterior scale margins on post-orbital portion of opercle creating three dark red oblique bars or reticulations. Exposed branchiostegal membrane dark red. Iris light blue to golden. Dorsal and anal fins light blue proximally and medially, with dark red stripes parallel to fin rays, and plain dark red distally. Caudal fin plain dark red. Pelvic fin plain red. Pectoral fin dark red.

Live female ( Fig. 4 D ): scales on trunk and head pale grey-brown, darker on dorsum and lighter to silver on venter. Scales with dark grey-brown margin, creating reticulation on trunk. Light blue iridescence on trunk and opercular region. Iris silver. All fins hyaline.

Distribution. Nothobranchius nikiforovi is currently known from temporary pools formed in the floodplain of the lower reaches of the seasonal Matandu River drainage ( Fig. 1 ). Three sites, including the type locality and the site of paratypes, are associated with the Zinga River, a south bank tributary of the Matandu River (indicated with ‘T’ for type locality and ‘P’ for paratype locality in Figure 1 ). A fourth known site is located further east, on the coastal floodplain associated with the lowermost part of the Matandu drainage.

Ecology. The lower reaches of the Matandu drainage in south-eastern Tanzania, where N. nikiforovi occurs, has a unimodal rainfall pattern extending from November to April, inferring an annual mode of reproduction in this species. The mean annual rainfall decreases southwards along the coast and is around 1000 mm at the Matandu River ( Hughes & Hughes 1992). Wetlands are at their lowest levels in August to September, when seasonal streams and most temporary habitats are dry.

The type locality is a small temporary pool formed in the drainage of the seasonal Zinga River, a tributary of the Matandu River ( Fig. 5 ). The habitat belongs to category 2.1.1 as defined by Watters (2014), representing ditches and excavated or eroded depressions associated with culverts along roads traversing the floodplain. At the end of the rainy season, the habitat was a shallow pool, about 10 m long and less than 5 m wide, and less than 1 m at the deepest point. At the type locality, all sampling took place in the same general habitat. The water was turbid, the bottom of the pool was not visible. Accompanying congeners consisted of N. cf. melanospilus . No water quality determinations were made at the time of collection of the type specimens. However, the second author, when visiting the paratype locality on June 7, 1997 during the mid-afternoon, determined the following water conditions: pH = 7.8, total dissolved solids = 440 ppm, temperature = 26 °C.

Conservation status. Nothobranchius nikiforovi is recommended to be listed as Vulnerable. The species is currently known from four sites, belonging to three threat-based locations. The species might exist at some other sites within the drainages associated with the lower Matandu but its distribution will remain restricted and any potential additional populations are expected to be fragmented. The extent of occurrence is expected to be less than 5,000 km ² and the maximum number of threat-based locations is estimated as ten. Using IUCN version 3.1 (2012), the species meets the criteria B1ab(iii) for Vulnerable.

The increasing pressure on land and water resources of wetlands will continue to result in habitat degradation and represent and important threat to the species, raising vulnerability in terms of conservation status. In combination with its seasonal life cycle in ephemeral habitats, its dependence on the clay-rich vertisol-type substratum for embryonic development makes the species more exposed to threats ( Nagy & Watters 2020).

No conservation measures are in place for this species, and it is not known from any protected areas. There is a need for improved habitat protection at the locations where the species is known to occur. Additional surveys targeting suitable habitats should be conducted in the region in order to better understand the geographic distribution of this species and to elaborate the appropriate measures of conservation.

Biology. Aquarium maintenance of selected specimens was undertaken for observation of breeding behaviour and biology. Nothobranchius nikiforovi has an annual mode of reproduction, typical of the genus. Eggs are deposited in the habitat substrate, where they survive the dry season and hatch with the onset of the wet season. Under captive conditions, peat moss was used successfully as an artificial spawning substrate. An embryonic development period of three to four months was observed at a temperature of about 22–24 °C.

Etymology. The specific name is given in honour of Andrei Nikiforov, from Russia, who participated in several field surveys aimed at research on Nothobranchius fishes in Tanzania, and he is co-discoverer of the new species and co-collector of the type specimens. A noun in genitive.

Figures

FIGURE 1. Map of eastern Tanzania, showing the known distribution of Nothobranchius nikiforovi (blue and red filled diamonds for blue and red phenotypes, respectively) and N. eggersi (blue and red filled circles for blue and red phenotypes, respectively). 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. T, type locality; P, site of specimens included in paratypes. Map prepared by B.R. Watters.

FIGURE 4. Nothobranchius nikiforovi, A. holotype, male, MRAC 2021.001.P.0001, 24.4 mm SL; Tanzania: lower Matandu drainage: Zinga system: ephemeral pool, about 9 km SE of Njinjo; B. live wild-caught male of blue phenotype from the type locality, Tanzania: lower Matandu drainage: Zinga system: ephemeral pool, about 9 km SE of Njinjo, about 30 mm SL; C. live wild-caught male of red phenotype, Tanzania: lower Matandu drainage: Zinga system: ephemeral swamp, about 32 km SW of Njinjo, about 30 mm SL; D. captive bred female from the type locality, about 20 mm SL. Photographs by B. Nagy (A, D) and A. Nikiforov (B, C).

FIGURE 5. Type locality of Nothobranchius nikiforovi; Tanzania: lower Matandu drainage: ephemeral pool, about 9 km southeast of Njinjo township. Photographed on 14 June 2017.