Alestopetersius conspectus, Munene, José Justin Mbimbi Mayi & Stiassny, Melanie L. J., 2012

Munene, José Justin Mbimbi Mayi & Stiassny, Melanie L. J., 2012, A new Alestopetersius (Characiformes: Alestidae) from the Kwilu River (Kasai basin) of central Africa; with a phylogeny for the genus and synonymy of Duboisialestes, Zootaxa 3166, pp. 59-68 : 64-67

Alestopetersius conspectus , new species

Fig. 4

Holotype. AMNH 253473, 3, 52.9 mm SL, Democratic Republic of Congo, Bandundu Province, Kwilu River at Carrefour, 05.19160° S, 18.94947° E, Coll. J.J. Mbimbi Mayi Munene, 24 February 2011.

Paratypes. AMNH 253475, 9 specimens, 42.3–53.6 mm SL, 2 CS, same data as holotype.— AMNH 253476, 10 specimens, 45.5–56.9 mm SL, 2 CS, Democratic Republic of Congo, Bandundu Province, Kwilu River at Kwilu beach, 05.04810°S, 18.83968°E, Coll. J.J. Mbimbi Mayi Munene, 19 February 2011.— AMNH 253477, 5 specimens, 42.4–49.2 mm SL, Democratic Republic of Congo, Bandundu Province, Democratic Republic of Congo, Bandundu Province, Kwilu River at Mbuji, 05.07180°S, 18.86935°E, Coll. J.J. Mbimbi Mayi Munene, 22 February 2011.— MRAC B1-19-P-5-6, 2 specimens, 44.8–44.9 mm SL, same data as holotype.— ZSM 40759, 2 specimens, 45.4–53.0 mm SL, same data as AMNH 253476.—CU 96797, 2 specimens, 42.3–44.3 mm SL, same data as AMNH 253477.

Diagnosis. Alestopetersius conspectus , new species, is distinguished from A. smykalai , A. leopoldianus , A. nigropterus , A. caudalis , and A. sp. “mbuji” in the possession of 12 (vs. 10) circumpeduncular scales. It is readily distinguished from A. brichardi , A. compressus , A. hilgendorfi , and A. tumbensis in the possession of a caudal-fin pigmentation consisting of a median black band extending to the caudal-fin margin and flanked by dense black bands in both upper and lower fin lobes. Alestopetersius bifasciatus , which shares similar caudal fin pigmentation, is distinguished from A. conspectus by the absence of a broad mid-lateral band on the body, and in tooth morphology.

Description. Medium-sized species, maximum size 56.9 mm SL. See Figure 4 for general appearance and Table 1 for summary of morphometric and meristic data. Relatively gracile and shallow-bodied, body depth 26.4– 34.5 % SL (mean 32.1), greatest depth at vertical through pelvic-fin insertion. Head length 20.4–29.7 (mean 27.5), eye large, bony orbit diameter 28.2–37.2 % HL (mean 34.9). Dorsal head profile straight from upper lip to nape, gently convex from that point to dorsal-fin origin. Dorsal body profile gently convex along dorsal-fin base to caudal-fin base, ventral body profile gently convex between isthmus and anal-fin base, caudal peduncle slightly longer than deep.

Mouth terminal, lower jaw prominent and slightly prognathous. Premaxilla with two teeth in outer row, each bearing five cusps, positioned opposite interspaces between and alternating with, four inner row teeth, each bearing 6–8 cusps ( Fig. 5 ). Outermost premaxillary tooth is markedly compressed and elongate with 7 or 8 small evenly sized cusps and a low median cusp. Dentary with four teeth in outer row, each bearing 6 or 7 cusps, outermost tooth smallest in jaw. No inner row teeth on dentary.

Dorsal-fin rays, ii 8 anal-fin rays iii, 18-20 (mode 19). Origin of dorsal fin slightly in advance of vertical through pelvic-fin insertion. There is muted sexual dimorphism in fin shape; anal-fin margin convex in mature males, and concave in females and juveniles. The first 4 or 5 branched rays of dorsal fin of mature males somewhat elongated and filamentous.

Body covered with small, regularly imbricate scales. Lateral line complete, with 31–34 pored scales to caudal flexion, 6.5–7 scale rows between lateral line and dorsal-fin insertion, 2.5 between lateral line and pelvic-fin insertion, 12 circumpeduncular scales. Twelve to 14 elongate gill rakers arrayed along lower limb of first arch. Total vertebral count 36 or 37 (mode 37).

Miscellaneous osteological features. Seven supraneurals are situated above the first seven rib-bearing vertebrae anterior to first dorsal-fin pterygiophore ( Fig. 6 A). This condition contrasts with that in most other species examined which possess only 6 supraneurals interdigitating with neural spines of six predorsal vertebrae ( Fig. 6 B). We note that Alestoptersius leopoldianus also exhibits 7 rib-bearing vertebrae anterior to dorsal fin pterygiophore, but unlike A. conspectus has 6 rather than 7 supraneurals. Both Alestopetersius tumbensis and Alestopetersius bifasciatus share the modal Alestopetersius configuration with 6 supraneurals interdigitating with 6 vertebrae anterior to the dorsal fin pterygiophore. The condition in the single individual of A. sp. “mbuji” is not discernable in radiographs.

Coloration. In alcohol ( Fig. 4 A&C), base body coloration pale creamy brown with darker basal crescents at contact zones of contiguous scales on dorsum. In males faint humeral stripe present above pectoral fin, but no trace of humeral stripe present in preserved females ( Fig. 4 C). In males ( Fig. 4 A) a broad black band extends from behind opercle, thickening gradually to caudal peduncle base, then narrows and extends to posterior caudal-fin margin. Distinctive broad black band in each caudal-fin lobe flank central black band and are separated from it by white bands. Remaining fins dusky hyaline, leading edge of pectoral fin dark brown or black. In females coloration similar but mid-lateral band and caudal-fin bands somewhat muted ( Fig. 4 C). In life ( Fig. 4 B&D) all individuals are iridescent silver with greenish-copper reflections anterolaterally, becoming bluish on flanks and caudal peduncle. Mid-lateral band is obscured anteriorly on body but clearly marked on caudal peduncle. Markings on caudal fin as in preserved specimens but much of the white interspaces between black bands are bright orange.

Distribution. Currently known from the Kwilu River in the vicinity of Kikwit ( Fig. 1 ). Collections in the main channel of the Middle Congo River, the Kasai main channel in the region of Bandundu, and Lulua River (a neighboring tributary Kasai) did not recover any individuals of A. conspectus despite intensive sampling, suggesting that the species may be a Kwilu endemic.

Ecology and habitat. Numerous specimens of Alestopetersius conspectus were collected at all sample sites along a 35 km stretch of the river ( Fig. 1 ). Most were collected using seine nets at depths of between 1– 2 m. Water temperature in the shallows where most specimens were collected was between 21–22.5o C and pH ranged from 5.8–6.5. The Kwilu River at the sampling sites is between 15–40 meters wide and the banks are variously covered with dense, undisturbed riparian vegetation, heavily degraded urban areas, and cleared agricultural areas ( Mbimbi & Stiassny 2011).

Female specimens contain numerous, maturing eggs in the ovaries and males have enlarged testes suggesting that reproductive activity was approaching at time of capture (February). Short guts (ca. 60% of SL when unraveled) and large stomachs with 6–8 fleshy pyloric caeca are suggestive of a carnivorous diet, and all specimens examined contained large numbers of insect head capsules and disarticulated body parts, most of terrestrial origin, with a preponderance of ants and small midges presumably taken at the water surface.

Etymology. Conspectus , from the Latin, in reference to the conspicuous markings on the caudal fin and striking, bright coloration of the species in life.

Figures

FIGURE 1. Location of the Kwilu River, stars indicate collecting localities for Alestopetersius conspectus, new species. Inset photograph: locality of the holotype at Carrefour.

FIGURE 4. Alestopetersius conspectus, new species (A) AMNH 253473, 3, preserved holotype, 52.9 mm SL, (B) 3 paratype, immediately post mortem, (C) AMNH 253477, Ƥ, preserved paratype, 47.5 mm SL, (D) Ƥ paratype, immediately post mortem.

FIGURE 5. Alestopetersius conspectus, new species AMNH 253476, 46.3 mm SL; (A) mouth open in lingual view; (B) maxilla and premaxilla in right lateral view; (C) lower jaw in left medial view.

FIGURE 6. Anterior vertebrae and associated structures in (A) Alestopetersius conspectus, new species (AMNH 253476), (B) Alestopetersius caudalis (AMNH 238424).