Distichodus mbiniensis, Schmidt & Knobloch & Barrientos, 2021

Schmidt, Ray C., Knobloch, Elise C. & Barrientos, Christian, 2021, Cast netting new species: Integrative taxonomy of Distichodus notospilus (Characiformes: Distichodontidae) discovers new species and overlooked areas of endemism in Central Africa, Zootaxa 4952 (2), pp. 291-313 : 305-308

Distichodus mbiniensis sp. nov.

urn:lsid:zoobank.org:act:8B5B9875-DB26-4417-B719-0869D8CFA19E

Figures 2 , 3 , 4 , 7 , 8 , 9 ; Table 6

Holotype. USNM 451317 , ALC, 99.9 mm SL, voucher EqGui 2017_0127, Equatorial Guinea, Wele-Nzas, Rio Ntoro at Aconibe—Acurenam Rd. , 668 m elev, 1.29091° N, 10.9174° E, 2017 Equatorial Guinea expedition team, 23 June 2017.

Paratypes. MRAC 2020,005 ,P,0001, 1 ALC, 114.1 mm SL, voucher EqGui 2017_0128, collection information the same as the holotype .— MRAC 2020,005 ,P,0002, 1 ALC, 74.4 mm SL, voucher EqGui 2017_0135, collection information the same as the holotype .— MRAC 2020,005 ,P,0003, 1 ALC, 113.9 mm SL, collection information the same as the holotype .— USNM 451319 , ALC, 61.3 mm SL, voucher EqGui 2017_0130, collection information the same as the holotype .— USNM 451318 , ALC, 122.1 mm SL, voucher EqGui 2017_0129, collection information the same as the holotype .— USNM 451320 , 3 ALC, 78.4–119.0 mm SL, collection information the same as the holotype .— USNM 451324 , ALC, 73.7 mm SL, voucher EqGui 2017_0191, Equatorial Guinea, Wele-Nzas, Rio Nuik near Alam , 660 m elev, 1.64875° N, 11.08593° E, 2017 Equatorial Guinea expedition team, 27 June 2017 .— USNM 451321 , ALC, 108.6 mm SL, voucher EqGui 2017_0147, Equatorial Guinea, Wele-Nzas, Rio Abia at Evinayong—Aconibe Rd , 664 m elev, 1.31069° N, 10.86025° E, 2017 Equatorial Guinea expedition team, 23 June 2017 .— USNM 451322 , ALC, 113.8 mm SL, voucher EqGui2017_0149, collection information the same as USNM 451321 .— USNM 451323 , ALC, 90.3 mm SL, collection information the same as USNM 451321 .

Diagnosis. Distichodus mbiniensis is readily distinguished from the larger-bodied, higher-scale count Distichodus spp. (group B in Arroyave et al. 2020; D. antonii , D. atroventralis , D. fasciolatus , D. lusosso , D. mossambicus , D. sexfasciatus , D. langi , D. rostratus , D. engycephalus , D. kasaiensis , D. ingae , D. polli , D. petersii , D. nefasch , D. brevipinnis , and D. schenga ) in having fewer lateral line scales (40–42 versus>60) and in achieving a smaller maximum standard length (<15 cm versus> 30 cm). This new species is also distinguished from the smaller-bodied, lower-scale count Distichodus spp. (group A in Arroyave et al. 2020) in the following ways. Distichodus mbiniensis is distinguished from D. decemmaculatus and D. teugelsi in having two rows of teeth on the lower jaw versus one. Distichodus mbiniensis can be readily distinguished from D. noboli , D. hypostomatus , and D. maculatus in having fewer scales along the lateral line (40–42 versus 45, 53–60, and 75 respectively), and distinguished from D. rufigiensis in not having prominent vertical bars along the sides. Distichodus mbiniensis is distinguished from D. kolleri in having fewer dorsal-fin rays (16–18 total rays versus 21–26), and distinguished from D. altus and D. affinis in having fewer total anal-fin rays (13–14 versus 21–22). Distichodus mbiniensis is distinguished from D. notospilus in having more scales along the lateral line (41–42, rarely 40 versus 37–39, rarely 40; Tables 5 & 6), a much less prominent elongated dark spot at the base of the caudal fin, a shorter dorsal fin (21.4–27.2 versus 22.7–34.2% SL), and shallower caudal peduncle (11.8–13.0 versus 12.3–14.1% SL). Distichodus mbiniensis is distinguished from D. microps in having a deeper body (usually seven scales from LL to the pelvic fin versus six), a subterminal mouth versus the nearly inferior mouth of D. microps , a shallower (11.8–13.0 versus 12.4–14.2% SL) and shorter caudal peduncle (9.7–12.6 versus 11.9–14.8% SL), a larger eye (58.6–88.0 versus 56.7–80.4% of snout length, Figs. 4B , 5 , 7 , & 8), a wider subopercle ( Fig. 8 ), and a shallower infraorbital 1 with a more curved anterolateral margin versus a deeper infraorbital 1 with a more rectangular anterolateral margin in D. microps ( Fig. 8 ).

Description. Morphometrics and meristics for the holotype and paratypes of Distichodus mbiniensis are summarized in table 6. Holotype shown in figure 7 and the live color of the holotype and a paratype are shown in figure 9. Maximum sized observed: 122.1 mm SL. Body laterally compressed and moderately elongate. Dorsal profile with a convex curve from tip of snout to the vertical of anterior margin of eye, weakly concave from the vertical of the eye to posterior margin of head, and convex to origin of dorsal fin. Profile weakly convex from origin of dorsal to adipose fin origin; weakly concave from adipose fin origin to caudal fin. Ventral profile broadly convex from snout to origin of anal fin; weakly concave from anal-fin terminus to caudal fin. Body covered in relatively large ctenoid scales; extending over the proximal half of adipose fin and caudal fin.

Mouth subterminal; two rows of bicuspid teeth in the upper and lower jaws. Dorsal fin with convex margin; its origin just anterior to the vertical of the origin of the pelvic fins. Adipose fin two thirds the distance from dorsal-fin terminus to caudal fin origin; base entirely anterior to the vertical of anal-fin terminus; distal tip extending beyond vertical of anal-fin terminus. Caudal fin forked; upper and lower lobes slightly rounded with moderate point. Anal fin with concave margin; base nearly equal to longest ray. Pelvic-fin origin at mid-length of snout to caudal fin distance; nearly as long as head length. Pectoral-fin origin just posterior to vertical of posterior margin of subopercle; horizontal just inferior to inferior margin of subopercle; slightly longer than pelvic fin.

Coloration. Live coloration: in both large and small specimens the ground color is bronze with some yellow and gold along the sides of the head. Some dark melanophores on subopercle in larger specimens which appears to be absent in smaller specimens. Anal and pelvic fins bright red in smaller specimens; a darker brick-red in larger individuals ( Fig. 9 ). Pectoral fins, adipose fin, and caudal fin clear to yellow. The dorsal fin with prominent black spot originating at the base of the third or fourth ray and extending anteriorly at an angle to the first ray. In small specimens this black marking extends to the distal tip of the dorsal fin but only extends distally about two-thirds in larger individuals ( Figs. 7 & 9 ). The last third of the dorsal fin is clear to yellow in smaller specimens and a darker red to yellow in larger specimens. Typical coloration after preservation is shown in figure 7. Specimens are medium to dark brown along the back and upper quarter of sides, lighter below. Scales along sides have darker spot on anterior and poster margin providing an effect of light horizontal stripes. Pigmentation on opercle and subopercle, and the spot a base of caudal fin more distinct than in live specimens. Fins beige with the dorsal fin with distinct black marking as described previously.

Etymology. The specific epithet refers to the Mbini River which is the Ndowe name for the Rio Wele. The Ndowe are Bantu-speaking people that live along the coastal region in Equatorial Guinea.

Distribution. This species is only known from the upper Mbini River drainage (Rio Wele) in Equatorial Guinea but may also occur within this drainage in Gabon ( Fig. 2 ). Research expeditions in the Woleu R. ( Mbini River drainage) in Gabon discovered a new species of Synodontis , but no specimens of Distichodus were collected at that time ( Friel & Sullivan 2008). Distichodus mbiniensis was collected in relatively deep (~2 meters) pools with some flow. At the type locality they were collected in the outflow of a black-water reservoir impounded by the recent road construction. Additional sampling in the region is needed to determine how widespread this species is within the region. The expedition in 2017 was one of the first to collect fishes in the tributaries of the Mbini River in Equatorial Guinea.

Conservation Status. Distichodus mbiniensis is only known to occur within the upper reaches of the Mbini River drainage in Equatorial Guinea but may also occur in this drainage in Gabon. The extant of occurrence (EOO) for this species is estimated at 19,085 km 2, determined in the IUCN Freshwater Mapping Application, and the species likely occurs in less than ten threat-based locations. These locations are the mainstrem of the Mbini River and the major tributaries that flow into the Mbini River. The habitats of D. mbiniensis are under threat due to pollution and sedimentation caused by ongoing road construction and logging activities in the region. Due to the restricted EOO, fewer than ten threat-based locations, and ongoing threats in the region that are negatively affecting the quality and extant of habitat for D. mbiniensis , this species is assessed as Vulnerable in the IUCN Red List ( Schmidt et al. 2020 b)

Figures

FIGURE 2. Phylogeny of Distichodus spp. inferred from 996 bp of cytochrome b (A). Phylogeny inferred from concatenated dataset of 996 bp CYTB, 729 bp MYH6, and 627 bp of CO1(B). Posterior probabilities from Bayesian inference above major branches; above 0.95 not shown and branches with support values <70 were collapsed. Metadata and accession numbers for specimens included in the analyses shown in table 1 and average uncorrected p-distances among these different taxa shown in table 3.

FIGURE 3. Phylogeny of Distichodus spp. inferred from 627 bp of CO1. Posterior probabilities from Bayesian inference above major branches; above 0.95 not shown and branches with support values <70 were collapsed. Metadata and accession numbers for specimens included in the analyses shown in table 1 and average uncorrected p-distances among these different taxa shown in table 3.

FIGURE 4. Plot of PC2 and PC3 from principal component analysis of 24 log-transformed measurements from 51 specimens (A). Reduced-major axis regression of eye diameter as a percentage of snout length on log-transformed standard length (B). Trendlines are shown for each species; slopes for each species are not different (p-value = 0.7613), and the elevation among species are significantly different (p-value = 0.0002) with Distichodus microps being significantly different (p-value <0.01) from D. mbiniensis and topotypic D. notospilus. The holotype of Distichodus microps and D. mbiniensis are denoted by a filled triangle and star respectively. Component loadings and results of Mann-Whitney U tests shown in table 3.

FIGURE 5. Distichodus microps, a new species, holotype, USNM 451325, ALC, 98.0 mm SL, Equatorial Guinea, Litoral, Rio Mbia at Menzong, 32 m elev, 2.07529° N, 9.92378° E; Photograph by S. Raredon.

FIGURE 7. Distichodus mbiniensis, a new species, holotype, USNM 451317, ALC, 99.9 mm SL, voucher EqGui2017_0127, Equatorial Guinea, Wele-Nzas, Rio Ntoro at Aconibe—Acurenam Rd., 668 m elev, 1.29091° N, 10.9174° E; Photograph by S. Raredon.

FIGURE 8. Lateral views of head region in Distichodus microps sp. nov. (A), Distichodus mbiniensis sp. nov. (B), and topotypic Distichodus notospilus (C). Same specimens and locality information as previous figures. Photographs by S. Raredon.

FIGURE 9. Live coloration of Distichodus microps, USNM 451457, ALC 81.6 mm SL, voucher EqGui2017_0274, Equatorial Guinea, Litoral, Rio Mbia at Menzong, 32 m elev, 2.07529° N, 9.92378° E photograph by R.C. Schmidt (A); Distichodus mbiniensis, USNM 451319, ALC 61.3 mm SL, voucher EqGui2017_0130, Equatorial Guinea, Wele-Nzas, Rio Ntoro at Aconibe—Acurenam Rd., 668 m, 1.29091° N, 10.9174° E, photograph by R. C. Schmidt (B); Topotypic Distichodus notospilus, OS 19544, ALC, 104.1 mm SL, Gabon, Province de l’Ogooué-Lolo, Right bank of Ogooué River at Doumé village, 0.84245° S, 12.96249° E, Photograph by B. Sidlauskas, included with permission (C); Holotype of Distichodus mbiniensis, USNM 451317, ALC, 99.9 mm SL, voucher EqGui2017_0127, Equatorial Guinea, Wele-Nzas, Rio Ntoro at Aconibe—Acurenam Rd., 668 m elev, 1.29091° N, 10.9174° E; Photograph by R. C. Schmidt (D).