Comprehensive DescriptionRead full entry
Bryconops magoi ZBK n. sp.
(Figs. 3c -4)
Holotype . MBUCV-V- 30782 (64 mm SL); Venezuela : Anzoátegui : Río Moquete at Paso Bajito, AN; L. Aguana, 4 Feb.1984 .
Paratypes . All lots collected at type locality, but some with different dates and/or collectors. MBUCV-V- 30783, 10 (17.0-54.0 mm SL) . FMNH 113936, 2 (35.5-55.5 mm SL) (preceding two series collected with holotype) . MBUCV-V- 30784, 2 (52.5-53.0 mm SL); A. Machado, 4 Oct.1984 . FMNH 113937, 2 (40.0-45.5 mm SL); A. Machado, 4 Oct.1984 . MBUCV-V- 30785, 6 (56.2-69.5 mm SL); A. Machado, 1 Feb.1984 . FMNH 113938, 3 (65.0-67.0 mm SL); A. Machado, 1 Feb.1984 .
Diagnosis. A species of Bryconops , subgenus Bryconops , that is distinguished from all other congeners except B. collettei ZBK by its unique color pattern, in which red coloration occupies the upper half of a diffuse caudal fin ocellus. It is further distinguished from members of the subgenus Bryconops by the following traits: pored lateral scales 43-47, modally 44 or 45 (>57 in B. alburnoides , <31 in B. disruptus and B. durbini , and 44-48, modally 47 in B. collettei ZBK ); pored lateral scales extending 2-3 scales beyond end of hypural plate onto caudal fin rays (pored lateral scales reaching end of hypural plate and not onto caudal fin rays in B. caudomaculatus ); snout length 5.8-8.0% SL, mean 6.8% (4.2-5.4%, mean 4.7% in B. collettei ZBK ); length of anal fin base 24.8-27.9%, mean 26.6% (27.3-29.8% SL, mean 28.8% in B. collettei ZBK ); and total vertebrae 40-42, modally 41-42 (42-44, modally 42-43 in B. collettei ZBK ).
Description. Morphometric data are given in Table 1 and a summary of meristic data appears in Table 2. A moderate to small-sized species of Bryconops , known from specimens less than 70 mm SL. Overall body shape with convex dorsum and slightly rounded belly, tapering to relatively short and deep caudal peduncle 10.5-13.9 (12.0 % SL). Dorsal fin origin at level of pelvic origin, almost at center of the body 49.0-52.3 (50.5 % SL).
Head 23.6-27.8 (25.5 % SL); posterior margin of opercle slightly sinusoidal. Border between second and third infraorbitals with naked ventral area; third infraorbital moderatedly developed, not reaching preopercle ventrally or at angle (Fig. 5). Eye large, 8.8-11.3 (9.8 % SL). Snout bullet-shaped; mouth terminal, opening just ventral to horizontal diameter through orbit. Maxilla extending posteriorly not reaching posterior
margin of the 2n infraorbital., length 5.8-8.0 (6.8 % SL). Ventroanterior margin of maxilla not heavily recurved (Fig. 5). Outer two rows of premaxillary teeth small and not prominent. Premaxilla with 2-5 teeth, bearing 3 to 5 cusps. Inner premaxillary teeth uniformly five, with 5 to 7 cusps; teeth basically symmetrical. Maxilla without teeth, rarely a small and single unicuspid tooth. Dentary with 4-5 large teeth, bearing 5-7 cusps. Smaller dentary teeth few.
Dorsal fin with straight to slightly convex distal margin; either the first or second branched ray longest. Posterior base of dorsal fin separated from anterior base of adipose fin by 12 to 13 scales, irregularly arranged. Adipose fin with convex dorsal margin and straight ventral margin. Lobes of caudal unequal, upper with rounded tip, and lower lobe longer and more pointed. Anal fin origin at level of end of dorsal fin base, its base 24.8- 27.9 (26.6 % SL); distal margin slightly falcate in adults and straight in juveniles. Pelvic fin not reaching origin of anal fin; distal margin of pelvic fin rounded. Distal margin of pectoral fin pointed and slightly falcate, not reaching pelvic insertion.
Widths of scales on sides of body above lateral line and below row along dorsal fin greater than, or equal to, length of scale; anterior margins of these scales almost circular, somewhat irregular; circuli present on anterior two-thirds of scale; posterior field lacking circuli, possessing 2-3 centrally located, and almost parallel, striae.
Dorsal-fin rays: unbranched 2*(23); branched 9*(23); total 11*(23). Anal-fin rays: unbranched 3(5), 4*(17); branched 26(6), 27(9), 28*(6), 29(1); total 29(1), 30(7), 31(9), 32*(4), 33(1). Pectoral-fin rays 12*(11), 13(10). Scales: predorsal 9(1), 11(4), 12*(16); lateral 41(6), 42(10), 43*(7), 44(1); pored lateral-line scales 43(2), 44(10), 45*(10), 46(1), 47(1); P -L scales 1(1), 2*(12), 3(11); rows above lateral line 7*(11), 8(10); rows below lateral line 4*(11), 5(10). Gill rakers: upper 5*(2), 6(19); lower 8(1), 9(16), 10*(4); total 14(2), 15*(16), 16(3). Vertebrae: precaudal 17(1), 18*(26); caudal 23(14), 24*(13); total 40(1), 41(13), 42*(13); dorsal-fin origin 11*(25), 12(2); anal-fin origin 17(1), 18*(26).
Pigmentation in alcohol. Overall moderate dusky species in preservation, countershaded above and below lateral stripe. Dorsal profile of head dark, fully covered with fine melanophores homogeneously distributed. Anterior area of mouth dark. Nares not covered with pigment. Orbit with a black dorsal band. Infraorbitals and preopercle sparsely pigmented, more conspicuous at sutures. Opercle with star-like diffused spots, more evident in dorsal region. Lateral stripe originating just behind head, somewhat prominent in preservation; increasing in depth and intensity just posterior to dorsal fin origin, occupying three to four scale rows just behind midbody and ending in darker, oblong-shaped expansion just anterior to caudal fin. Centers of upper lateral scales pigmented densely. First 14 scales of lateral line canal outlined with pigment. Below lateral line, melanophores distributed along myosepta from just anterior to anus to midpoint of anal fin. Anal-fin base with a diffuse basal band formed by series of melanophores along pterygiophores. Dorsal, pectoral, and pelvic fins with melanophores outlining lower portion of fin rays. Adipose fin lacking melanophores. Both lobes of caudal fin densely covered by melanophores. A clear but diffuse area on anterobasal part of upper caudal lobe, not forming a well-defined ocellus. Distal margin of caudal fin area with a dark, almost black terminal band, especially on upper lobe.
Coloration in life (Fig. 3c). Body usually grayish or metallic dorsolaterally, becoming silvery toward lateral and ventral flanks. A black lateral stripe extends from opercular opening to caudal fin base. Below this stripe there is a wider silvery stripe, limited dorsally by an iridescent metallic-yellow stripe.
Head silver laterally. Iris yellow dorsally and silver ventrally. Cheek and opercular regions silvery. Dorsal part of head, snout and lower jaw dark. Dorsal fin slightly orange. Pectoral, pelvic and anal fins transparent. Adipose intense red. Caudal fin with dark distal margin, especially on upper lobe. Caudal-fin lobes with transparent areas near fin base diffuse and without well-formed ocelli. Upper lobe with red coloration in upper part of the diffuse area, the red extending posteriorly beyond this area, almost to end of the fin rays.
Distribution. This new species is only known from the type locality, the Río Moquete, Anzoátegui State, Venezuela. The Río Moquete is a northern tributary of the Río Orinoco.
Habitat. Bryconops magoi ZBK is known only from a morichal with fast moving waters over sandy bottoms. This species frequently is found in water from mid-depth to the surface, at the center of the main channel, where it schools with other characid species. Individuals feed at the surface and are attracted to allotochtonus material that falls into the water. Cursory examination shows that they feed on several groups of terrestrial insects.
Etymology. The species-group name, magoi, is dedicated to the memory of Dr. Francisco Mago-Leccia, pioneer of modern ichthyological studies in Venezuela.
Comparison with B. collettei ZBK . Bryconops magoi ZBK differs in body shape from B. collettei ZBK . The results of sheared principal components analysis and relative warp analysis show that all individuals of both species are discriminated by either the second sheared principal component (Fig. 6) or by the first relative warp. In both analyses all individuals of B. magoi ZBK fell at, or inside, the boundary of the 95% confidence ellipse, whereas three individuals of B. collettei ZBK fell just outside the 95% confidence ellipse, but with a morphology most different from B. magoi ZBK (Fig. 6). The first two eigenvectors of the PCA described 99.1% of the variance. The second sheared PC identified a contrasting suite of traits such that B. magoi ZBK has a longer snout and B. collettei ZBK has a longer anal fin base, a larger orbit, and a greater distance between the dorsal fins (Fig. 7). RWA produced identical results to the PCA. Even though individuals of B. collettei ZBK from the Río Iguapo have slightly longer snouts relative to other populations, there is no overlap in snout length between the species. For each of the other metric traits the differences between the species are statistically significant, but there is some overlap between the species.