A New Alestes (Characiformes, Alestidae) from the Mpozo River in the Democratic Republic of Congo
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Copeia 2009, No. 1, 110–116 A New Alestes (Characiformes, Alestidae) from the Mpozo River in the Democratic Republic of Congo Melanie L. J. Stiassny1, Robert C. Schelly1, and Victor Mamonekene2 A new species of Alestes from the Mpozo River in the Bas Congo Province of the Democratic Republic of Congo is described and diagnostic characters for the genus are presented. Alestes inferus, new species, is differentiated from all other members of the genus by its lower and non-overlapping lateral-line scale count (31–33 versus 36–51) and its reduced and non-overlapping vertebral count (39–40 versus 41–49). Within Alestes, the new species appears to be most closely related to A. macrophthalmus and A. liebrechtsii, based on the shared possession by these three species of a tubular, bony extension enclosing the olfactory nerve on the lateral ethmoid, and bifurcated lateral-line canals terminating in two pores. Alestes liebrechtsii and A. inferus are the only species of the genus known from the lower Congo River. Une nouvelle espe`ced’Alestes est de´crite de la rivie`re Mpozo dans la Province du Bas-Congo en Re´publique De´mocratique du Congo et les caracte`res de diagnose sont donne´s. Alestes inferus sp.nov. se distingue des autres membres du genre par un nombre re´duit, sans chevauchement, d’e´cailles de la ligne late´rale (31–33 contre 36–51), de meˆme qu’un nombre re´duit, sans chevauchement, de verte`bres (39–40 contre 41–49). Parmi les Alestes, la nouvelle espe`ce semble proche de A. macrophthalmus et de A. liebrechtsii du fait de la pre´sence chez ces trois espe`ces d’une extension osseuse tubulaire entourant le nerf olfactif sur l’ethmoı¨de late´ral et des canaux de la ligne late´rale se terminant par deux pores. Alestes liebrechtsii et A. inferus sont la seule espe`ces du genre connue du cours infe´rieur du Congo. ECENT collections made in the Mpozo River just measurements follow Paugy et al. (2003), with three upstream of its confluence with the Congo main- exceptions. Vertebral counts include the four modified R stream have revealed the presence of a new species of Weberian centra but exclude the terminal, hypural-bearing Alestes in that Congo River affluent. This brings to two the vertebra. Gill raker counts in Table 1 correspond to the number of Alestes species found in the lower Congo region. number of rakers arrayed along the lower limb of the first Paugy (1986) records the presence of a single specimen of arch and exclude the raker in the angle of the arch. Alestes macrophthalmus from ‘‘Congo a` Brazzaville,’’ and it is Longitudinal and lateral-line scale counts terminate at the possible that A. macrophthalmus occurs in the region of Pool hypural fold and do not include the one or two scales over Malebo. However, as far as can be ascertained, prior to the the base of the caudal fin. Throughout this paper, the present study only a single species of Alestes, A. liebrechtsii, phylogenetic species concept is adopted as a basis for species which is well-represented in our mainstream lower Congo diagnosis, and in the accompanying illustrations an asterisk River collections, has been reliably reported from the lower precedes character numbers discussed in the text. Based on Congo region. The new taxon, which shares the synapo- outgroup comparison undertaken in the present study and morphies of Alestes, is readily differentiated from all known on the phylogenetic analysis of Zanata and Vari (2005), the members of the genus and is described herein. use of superscript 1 indicates the hypothesized derived state Although there currently exists no consensus regarding and superscript 0 the plesiomorphic state for each figured the precise relationships of the genus Alestes within the character. characiform family Alestidae (Brewster, 1986; Murray and Stewart, 2002; Calcagnotto et al., 2005; Zanata and Vari, Alestes inferus, new species 2005), none have disputed that the restricted concept of the Figure 1 genus (in the sense of Brewster, 1986 and Paugy, 1986) represents a monophyletic entity. Most recently, Zanata and Vari (2005) provide a list of seven anatomical features Holotype.—AMNH 242136, male, 85.7 mm SL, Democratic optimized as synapomorphic for Alestes sensu stricto. Three of Republic of Congo, Bas Congo Province, Mpozo River main these characters are confirmed as unique and unreversed channel at bridge near confluence with Congo River even among characiforms broadly, and are employed herein mainstream, 5u50950S, 13u299420E, 15 July 2007. in a phylogenetic diagnosis for Alestes. Paratypes.—AMNH 242137, 90.8–78.1 mm SL (4 alcoholic) same data as holotype, AMNH 242138, 94.3–78.0 mm SL (2 MATERIALS AND METHODS alcoholic, 2 cleared and stained), Democratic Republic of Visualization of canal-bearing scales and teeth was aided by Congo, Bas Congo Province, Mpozo River main channel at directing a fine jet of compressed air onto the structures. In bridge near confluence with Congo River mainstream, order to count vertebrae and fin rays, and to visualize other 5u50950S, 13u299420E, 18 July 2007. skeletal features, all specimens were radiographed and some were cleared and stained following a modified protocol Diagnosis.—Distinguished from all congeners by the posses- based on Taylor and Van Dyke (1985). Counts and sion of fewer pored scales along the lateral line (31–33 versus 1 American Museum of Natural History, Department of Ichthyology, Central Park West at 79th Street, New York, New York 10024; E-mail: (MLJS) [email protected]; and (RCS) [email protected]. 2 Institut de De´veloppement Rural, Universite´ Marien Ngouabi, B.P. 69 Brazzaville, Republic of Congo; E-mail: [email protected]. Submitted: 28 November 2007. Accepted: 3 September 2008. Associate Editor: C. J. Ferraris. F 2009 by the American Society of Ichthyologists and Herpetologists DOI: 10.1643/CI-07-252 Stiassny et al.—New Alestes from Lower Congo 111 Table 1. Morphometric and Meristic Data for Holotype and Eight 36–51) and fewer vertebrae (39–40 versus 41–49). Alestes Paratypes of Alestes inferus, New Species. inferus is further differentiated from A. dentex, A. baremoze, and A. stuhlmanni in the possession of fewer gill rakers along Holotype + Paratypes the lower limb of the first arch (15–17 versus 23–58). Morphometrics holotype min max n mean Description.—A medium-sized species, maximum observed Standard length (mm) 85.7 78.0 94.3 9 84.4 size 94.3 mm SL. Relatively elongate, laterally compressed % head length with greatest body depth at or near dorsal-fin origin (mean Eye diameter 35.4 34.3 38.5 9 37.4 body depth 29.6% SL). See Figure 1 for general appearance Interorbital width 35.9 35.3 38.3 9 36.3 and Table 1 for summary of morphometric and meristic data. Dorsal body profile gently convex to caudal peduncle, % standard length except for a straight portion along dorsal-fin base, ventral Head length 24.7 24.3 25.8 9 25.3 profile more convex than dorsal and smoothly rounded to Body depth 29.3 28.7 30.4 9 29.6 anal-fin insertion. Caudal peduncle longer than deep. Predorsal length 49.0 47.2 51.8 9 48.4 Mouth terminal, gape not reaching beyond vertical through Dorsal-adipose 26.8 24.6 26.9 9 26.1 anterior margin of eye. Lower jaw robust. Lower lip thick, Caudal peduncle length 11.9 10.9 12.8 9 11.9 forming pad of tissue in front of dentary tooth row. Eye Caudal peduncle depth 10.1 9.2 10.1 9 9.7 relatively large, bony orbit diameter 34.3–38.5% HL, covered by well-developed adipose membrane with broad ovoid slit Meristics Holotype Paratypes exposing large pupil (Fig. 2). Total number of vertebrae 40 39(6) 40 (2) Premaxilla with three teeth in outer row, each bearing Dorsal fin rays (branched) 8 8 threeorfourcusps,insmootharc(non-alternating), Anal fin rays (branched) 18 16(1) 17(4) 18(3) positioned over anterior inner row teeth, not interspaced Gill rakers (lower limb) 16 15(1) 16(3) 17(4) between them (Fig. 3A). Four inner row teeth on each Lateral-line scales 31 33 premaxilla, the anterior two teeth with an expansive base Lateral line–dorsal fin scale rows 5.5 5.5(3) 6(5) almost as deep as wide, with paired molariform cusps Lateral line–pelvic fin scale rows 2.5 2.5 distally and seven to eight pointed cusps proximally Circumpeduncular scales 12 11(3) 12(5) (Fig. 3B). Third premaxillary tooth bears a slight postero- medial expansion at its base and closely abuts anterior margin of fourth, narrow-based inner row tooth. Four outer Fig. 1. Alestes inferus, new species (A) AMNH 242136, preserved holotype, 85.7 mm SL, (B) AMNH 242137, paratype, 86.0 mm SL, immediately post mortem. Scale bar indicates 1 cm. 112 Copeia 2009, No. 1 Fig. 2. Alestes inferus, new species, left lateral schematic of head and superficial cranial anatomy. row teeth on contralateral dentaries, each with large central cusp and two to four minor cusps on either side (Fig. 3C). First three teeth have somewhat expanded bases but lack molariform distal cusps. Fourth tooth is markedly smaller than preceding three. A single pair of large, conically recurved, symphyseal inner row teeth on lower jaw Fig. 3. Alestes inferus, new species AMNH 242138, 81.3 mm SL; (A) invariably present (Fig. 3B). maxilla and premaxilla in right lateral view; (B) mouth open in lingual Dorsal-fin rays ii, 8; anal-fin rays iii, 16–18. Origin of view; (C) lower jaw in right lateral view.