Characidium longum B., Montaña & Buckup, 2006, new species

Characidium longum, new species (Fig. 1)

Holotype: MCNG 53371, 31.8 mm SL; Venezuela: Apure, Rio Capanaparo drainage: Caño La Guardia (06.84000ºN, 67.32500ºW), C. Montaña, 14 Mar 2005.

Paratypes (all from Venezuela): MCNG 52732 (33, 33.2-34.8), ANSP 180809 (1, 32.7), EBRG 9839 (1, 30.4), FMNH 116483 (1, 32.3), MBUCV 32712 (1, 29.2), MHNLS 18203 (1, 28.6), NRM 52454 (1, 30.1), MNRJ 28711 (5, 29.4-32.7), all collected with holotype; ANSP 159795 (1, 27.0), Amazonas: Rio Sipapo, about 4 km upstream from Pendare (04.86666ºN, 67.71666ºW), H. López et al., 12 Nov. 1985; ANSP 180818 (2, 41.6-44.7), Amazonas: Rio Ventuari, village of Marueta at landing, 91 km ENE of Macuruco, 159 km ENE of San Fernando de Atabapo (4.31416ºN, 66.29221ºW), M. Sabaj et al., 6 Apr. 2004; ANSP 182783 (1, 33.7) Amazonas: Rio Manapiare: 10 km NW of San Juan de Manapiare (05.38694ºN 66.95000ºW); AUM 42937 (1, 45.0), Amazonas: Rio Orinoco, beach on island in middle of river, 32 km SSE of Manaka, 91 km ESE of San Fernando de Atabapo (03.70278ºN, 66.96112ºW), N. Lujan et al., 3 Mar. 2005; AUM 42938 (1, 41.0), Amazonas: Rio Orinoco, 117 km E of La Esmeralda (03.28988ºN, 66.60004ºW), N. Lujan et al., 29 Mar. 2005; AUM 42940 (2), Amazonas: Rio Casiquiare, 153 km NE of San Carlos de Rio Negro (02.79877ºN, 66.00652ºW), N. Lujan et al., 24 Mar. 2005; FMNH 103919 (1, 41.0), Amazonas: Rio Cataniapo at bridge crossing ca. 5 km from Puerto Ayacucho just below small rapids, B. Chernoff et al. 21 Jan. 1991; FMNH 103923 (1, 35.0), Amazonas: Rio Sipapo about 1 km above mouth of Rio Cuao (06.95700ºN, 67.72000ºW), B. Chernoff et al., 8 Feb. 1992; FMNH 109945 (1, 28.0), Bolivar: Rio Icutú, at mouth of Caño Wani (06.07450ºN, 67.92000ºW), F. Provenzano et al., 6 Dec 2000; FMNH 109946 (2), Bolivar: Caño Wani, (06.07971ºN, 67.92221ºW), F. Provenzano et al., 6 Dec. 2000; MBUCV 14090 (1), Amazonas: Rio Cataniapo, Port of the community of Las Pavas (05.56666°N, 67.55555°W), R. Royero et al., 24 Jan 1969; MBUCV 14531 (1), Amazonas: Rio Cataniapo, Beaches upstream from base camp; R. Royero et al., 25 Jul. 1982; MBUCV 25850 (1), Amazonas: Rio Orinoco, 0.5 km up from La Esmeralda on beach (03.11666°N, 65.55000°W), B. Chernoff et al., 12 Mar 1987; MBUCV 30585 (2), Bolivar: Rio Caura, Rio Nichare island on the main channel Wakawakai (6.32250°N, 64.95366°W), F. Provenzano et al., 6 Dec. 2000; MBUCV 31743 (1), Bolivar: Rio Caura, Rio Nichare in creek close to Tawadu River near of the Dedemai station (06.35150°N, 64.99850°W), F. Provenzano et al. 7 Dec. 2000; MCNG 21641 (6, 38.5-43.0), Amazonas: Rio Guayapo 149 km from its confluence with the Río Sipapo (04.38333°N, 67.03333°W), L. Nico & E. Guayamare, 20 May 1989; MCNG 22400 (6, 40-45.6), Bolívar: Rio Nichare, beach at base of Icutú Falls, in first stream on right traveling downstream (05.88333°N, 64.85000°W), D. Taphorn, et al., 12 Dec. 1989; MCNG 22545 (2, 43.1-44.6), Bolívar: upper Río Nichare, at gravel beach upstream from Caño Icutú (06.08194°N, 64.91667°W), D. Taphorn et al., 15 Mar. 1989; MCNG 22872 (15, 47.7-48.4), Bolívar, Río Nichare, Alto Río Nichare (06.0850°N, 64.93417ºW), D. Taphorn et al., 18 Mar. 1989; MCNG 23008 (2, 36.2-51.7), Bolívar: Río Nichare, Caño Tabaro 3 km up from mouth of Rio Nichare (06.36722ºN, 64.96694°W), D. Taphorn et al., 24 Mar. 1989; MCNG 23797 (12, 38.1-40.7), Amazonas, Río Matacuni, in front of campsite N° 4 (03.6830ºN, 65.00277ºW), B. Stergios, 25 Jan. 1990; MCNG 34823 (4, 33.2-42.3), Bolívar: Río Nichare, La Raya rapids, 1 km from mouth of Rio Nichare, (06.55000°N, 64.84167ºW), D. Rodríguez et al., 30 Mar. 1997; MCNG 35024 (2, 34.8-36.5), Amazonas: Río Casiquiare, playa de Macanilla (02.43306ºN, 66.45472°W); K. Winemiller & D. Jepsen, 31 Jan. 1997; MCNG 35913 (1, 36.6): Amazonas: Río Orinoco, Raudales Las Perezas (04.77965ºN, 67.4575ºW); O. León, 10 Sept. 1997; MCNG 36596 (1, 41.2), Bolívar: Río Caura, El Playón at Salto Para, (06.31666ºN, 64.48333ºW); D. Rodríguez et al., 28 Mar. 1997; MCNG 39251 (1, 29.2), Apure: Río Cinaruco, downstream from Laguna Larga (06.54167°N, 67.40139°W), A & J. Arrington, 11 Jan.1999; MCNG 39630 (7, 34.6-24.7), Apure: Río Cinaruco (06.54194°N, 67.40861°W), A. & J. Arrington, 11 Feb. 1999; MCNG 40644 (1, 31.4), Apure: Río Cinaruco (06.54194°N, 67.40861°W), A. & J. Arrington, 19 Mar.1999; MCNG 49728 (1, 29.0), Bolívar: Río Parguaza, near town of Parguaza (06.26000°N, 67.12450ºW), S. Willis & C. Montaña, 10 Jan. 2004; MCNG 52460 (29, 31.2-22.8), Apure: Río Capanaparo at Caño La Guardia (06.54444ºN, 67.33054ºW), C. Montaña, 20 Nov. 2005; MCNG 52653 (42), Apure: Río Capanaparo at Caño La Guardia (06.54444ºN, 67.33054ºW), C. Montaña, 15 Mar. 2005; MCNG 53074 (10, 28.7-38.8), Apure: Río Capanaparo at Caño La Guardia (06.54444ºN, 67.33054ºW), C. Montaña, 24 Feb. 2005; MCNG 53272 (165, 33.7-34.8 mm), Apure: Río Capanaparo at Caño La Guardia (06.54444ºN, 67.33054ºW); C. Montaña, 30 Nov. 2004; MHNLS 16694 (1, 36.7), Amazonas: Caño Gavilán, left bank tributary of Río Cataniapo (05.54138ºN, 67.39083ºW), J Fernández, 25 Mar. 2002; MHNLS 16937 (2, 40.4-45.7), Amazonas: Río Cataniapo (rapids with aquatic vegetation); J. Fernández, 25 Apr. 2002.

Non-type material examined (included on distribution map), all from Venezuela: MCNG 15973 (1), Bolívar: Río Chaviripa at the bridge on Caicara -Puerto Ayacucho road (07.13333°N, 66.50000ºW), D. Taphorn et al., 16 Apr. 1984; MCNG 17971 (2), Apure: Río Cinaruco about 75 minutes by boat from mouth, (06.62778°N, 67.20278°W), D. Taphorn & B. Stergios, 31 Dec. 1986; MCNG 20862 (1), Bolívar: upper Río Nichare, at beach of stones, upstream from Caño Chiguire (06.01556°N, 64.97944°W), D. Taphorn, et al., 17 Mar. 1989; MCNG 21178 (3), Bolívar: Río Nichare, downstream from Caño Icutú (06.10000°N, 64.916647°W), D. Taphorn & J. Pulido, 15 Mar. 1989; MCNG 21513 (4), Bolívar: Río Nichare, pool in front of Icutú Falls, on beaches (5.88361°N, 64.85000°W), D. Taphorn, et al., 10 Mar. 1989; MCNG 21876 (3), Amazonas: Río Orinoco, Isla Trucoapure beaches (03.00028°N, 67.66666°W), L. Nico & J. Castillo, 13 Feb. 1990; MCNG 22318 (1), Amazonas: Río Guayapo at Aguacate rapids, not far from the confluence with Río Sipapo (4.33333°N, 67.50000°W), L. Nico & E. Guayamare, 25 May 1989; MCNG 22423 (1), Bolívar: upper Rio Nichare, mud and sand beach (06.08694°N, 64.93417°W), D. Taphorn et al. 18 Mar. 1989; MCNG 22484 (2), Bolívar: Río Nichare (06.10278°N, 64.92500ºW), D. Taphorn & E. Sutton, 17 Mar. 1989; MCNG 22787 (3), Bolívar: small tributary of Caño Tabaro (05.88388°N, 64.85000°W), D. Taphorn et al., 22 Mar. 1989; MCNG 24009 (4), Amazonas: Río Ocamo at Caño Jayuvapuei (03.05000°N, 64.64167°W), L. Nico, 28 Jan. 1990; MCNG 25885 (1), Amazonas: Río Orinoco, downstream from town of Cariche (03.03333°N, 66.41667°W), L. Nico et al., 20 Jan. 1991; MCNG 26073 (2), Amazonas: Río Siapa, 176 km upstream from its confluence with Rio Casiquiare (01.41667ºN, 65.68333°W), A. Barbarino & F. Morillo, 17 Apr. 1991; MCNG 35152 (3), Amazonas: Río Casiquiare, sandy beach (2.39722°N, 66.51389°W), K. Winemiller & D. Jepsen, 28 Jan. 1997; MCNG 39179 (10), Apure: Río Cinaruco, upstream from Laguna Larga (06.55250°N, 67.42417°W), A. & J. Arrington, 11 Jan. 1999; MCNG 39184 (2), Apure: Río Cinaruco, upstream from Laguna Larga (06.55250°N, 67.42472°W), A. & J. Arrington, 11 Jan. 1999; MCNG 39197 (3), Apure: Río Cinaruco, upstream from Laguna Larga (06.53889°N, 67.42250°W), A. & J. Arrington, 11 Jan. 1999; MCNG 39453 (3), Apure: Río Cinaruco, downstream from Laguna Larga (06.55611°N, 67.37583°W), A. & J. Arrington, 16 Jan. 1999; MCNG 39576 (1), Apure: Río Cinaruco (06.54167°N, 67.40139ºW), A. & J. Arrington, 10 Feb. 1999; MCNG 39600 (3), Apure: Río Cinaruco (06.53889°N, 67.42250°W), A. & J. Arrington, 11 Feb. 1999; MCNG 44419 (1), Apure: Río Cinaruco beach upstream from Laguna Larga (06.55250°N, 67.42466°W), C. Layman, 15 Jan. 2001; MCNG 44498 (3), Apure: Río Cinaruco (06.54056°N, 67.41500°W), C. Layman, 15 Feb. 2001; MCNG 43678 (2), Amazonas: Río Negro, about 1 km upstream from San Carlos de Río Negro (01.91666°N, 67.08333ºW), L. Nico et al., 5 Jan. 1999.

Diagnosis

Characidium longum is distinguished from all congeners by its extremely elongate body (greatest body depth at dorsal fin origin 9.3-15.8 % SL, mean 12.6) and a pigmentation pattern of 13 or more thin black vertical bars along the sides (each with a concentrated spot of pigment on the midlateral line), which are united dorsally with reddish-brown blotches that cross the dorsum.

Characidium longum shares a similar pigmentation pattern of vertical bars with Characidium catenatum Eigenmann, 1909, described from Guyana, and Characidium zebra Eigenmann, 1909, described from the Rio Maripicru, a branch of the Ireng of the upper Río Branco drainage of Brazil; as well as Characidium fasciatum Reinhardt, 1866. Schultz (1944) described Characidium chupa from the Rio Chama, in the Lake Maracaibo basin, and indicated that this species also occurs in the Orinoco basin, including the upper Rio Apure and Rio Torbes (also see Buckup, 2003). Although these species (or similar forms) are present in Venezuela, they have at most 10 vertical bars, vs. 13 or more bars in Characidium longum. C. longum shares its characteristic pigmentation pattern of reddishbrown blotches on the dorsum (in both live and freshly preserved material) with the sympatric congeners C. pellucidum Eigenmann, 1910 and C. pteroides Eigenmann, 1909. However, neither of the latter two species has well-defined black vertical bars on the flanks. C. pellucidum has only a row of dark dots along the lateral midline, and C. pteroides has a series of irregularly placed reddish-brown crescents over a pale cream background (Figs. 2 and 3).

Description

Based on holotype (41.2 mm SL) and 20 paratypes (29.0-52.0 mm SL, mean 39.5), and with notes on variation among smaller specimens and non-type material. This size range is medium to large among Venezuelan species of Characidium. Measurements and counts are summarized in Table 1. Sexes appear to be isomorphic.

Body elongate and spindle shaped, not very compressed laterally. In alcohol the body is almost square in transverse section, probably as a result of shrinkage. Head dorsal profile straight, but many individuals were preserved with head arched up. Ventral profile strongly concave from tip of snout to isthmus. Dorsal profile only slightly convex from head to base of caudal fin. Ventral profile slightly convex from dentary tip to posterior anal fin, and straight between anal and caudal fin bases. Profile of tip of snout vertical. Greatest body depth just anterior to dorsal fin origin.

Mouth small, subterminal. Maxilla short, posterior end rounded and reaching vertical line downward from posterior nares, but not reaching anterior edge of orbit. Orbit ovalshaped, but not precisely oriented with horizontal axis of body; dorsal margins of eyes reaching, or sometimes elevated, above dorsal profile of head; eyes much longer than snout length; forming slight depression in interorbital space. Bony interorbital very narrow. Cheek height less than one-third of horizontal orbital diameter. Nares distinctly separated; posterior nostrils considerably closer to eye than to anterior nostrils; no dermal flaps on either nostril, but rims of each elevated above body to form raised rim. Supraorbital present and having a sensory canal.

Scales cycloid. Lateral line complete, containing 38-40 scales (counts: 38 [1], 39 [8], 40 [8]). Scale rows above and below lateral line 3 each. Circumpeduncular scales 12. Predorsal scales 9 (3), 10 (17). Isthmus and area between pectoral fin bases completely scaled. Caudal fin with sheath of scales extending caudally for more than half its length. Last scale in series on dorsal and ventral caudal-fin lobes larger than the rest.

Dorsal-fin rays ii,7 (2), ii,8 (3), ii,9 (15). Anal-fin rays ii,6 (21). Pectoral-fin rays iii,10 (14), iii,11(7). Pelvic-fin rays i,7 (2), i,8 (18), i, 9 (1). Caudal fin rays 11-10 (21). Adipose fin present, situated above posterior end of anal fin base.

All teeth tricuspid, with approximately equal cusps. Usually six small teeth arranged in one row on each side of both premaxilla and dentary. Maxilla toothless.

Gill rakers usually three short, widened stubs, best developed on dorsal portion of first arch, followed by one or two rudiments.

Pigmentation in alcohol (Fig. 1)

Base color of head and body creamy white. Snout with black stripe, which starts on maxilla and ends beneath posterior nostril. Premaxilla and area on dorsum of head between nares with sparse melanophores. Brain visible through dermal tissue, but covered with scattered melanophores that are concentrated into a black dot at posterior edge of brain, just in front of first predorsal scale. Ventral portion of head immaculate; eye densely covered with black pigment on upper two thirds; ventral portion white. Posterior border of head between upper edge of opercle to posterior part of brain with narrow black bar that forms an “L,” with short stripe of black pigment on upper edge of opercle. Dorsum with a series of about 13 clusters of reddish-brown pigment; same pigment outlines dorsal scales and sometimes becomes aligned to form an X pattern across dorsum; ventral-most reddish-brown pigment usually aligned with uppermost edge of black vertical bars on sides. Sides with series of thin vertical bars, often double, with concentrated dots of black pigment on lateral line scales, the bars not extending down to ventrum. Spot of black pigment, diagnostic of the genus Characidium (Buckup, 1993a,b) present at base of central caudal fin rays. Mid-ventral line behind pelvic fin base with thin single row of melanophores that ends before reaching anal origin. Anal-fin origin and base with concentration of black pigment, which forms a conspicuous dot. Pelvic fin with similar spot at origin. Dorsal fin with posterior rays thinly outlined in black posteriorly; adipose fin without pigment; caudal fin with spots of deep pigment at base of both upper and lower lobes (separate from similar dot at center of caudal fin base); central portion of caudal-fin rays thinly outlined, with melanophores that form a diffuse vertical bar when fin is closed. Anal fin with first five rays darkly pigmented near base. Pelvic and pectoral fins transparent.

Life colors

No photographs of living specimens are available. Live fish are similar to those described in alcohol, but the body is almost transparent, rather than whitish.

Distribution, habitat and diet (Figs. 4 and 5)

So far these fish have been found in the lower rios Capanaparo and Cinaruco of southern Apure state, in various rivers of the upper Orinoco basin, and the middle Rio Caura drainage. We have seen photographs of specimens from the Rio Morichal Largo system in Monagas state, Venezuela, and the upper Río Negro in Brazil that probably are this species.

Most specimens have been collected over sandy beaches in flowing, clear or teacolored, shallow water along shore (Fig. 4). We examined the contents of fifty stomachs and found that these fishes feed primarily on benthic aquatic invertebrates taken from the sand. Copepods were dominant, followed by water mites and chironomid larvae, with occasional items including ostracods and larvae of Ephemeroptera, Trichoptera, Coleoptera and Diptera.

Etymology

From the Latin adjective longus (-a, -um), long, in reference to the extremely elongated body of this new species.

Discussion

We are studying five additional species of Characidium from the western llanos of Venezuela, and preliminary results indicate that these all may prove to be new species. Four of these are considered to be Venezuelan representatives of Characidium catenatum, C. zebra, C. pteroides and C. pellucidum, described from neighboring drainages in Guyana or northern Brazil; and one is a stocky, deep-bodied, vertically striped form for which we have not yet determined its closest relationships. C. catenatum was considered to be a synonym of C. steindachneri by Buckup (2003), a species described from Peru. Therefore, the four Guyanan species are also in need of taxonomic revision. As Souto de Melo and Buckup (2002) have noted, species of the genus Characidium have not yet been adequately classified into subgroups, so we cannot presently propose a theory of relationships for the new species.

Characidium longum is similar to characidiin species of the genus Ammocryptocharax Weitzman & Kanazawa, 1976, in having an elongate, spindle-shaped body. However, in addition to the unique pigmentation pattern already described, C. longum lacks teeth on the maxilla and has a subterminal mouth, rather than the ventrally positioned mouth characteristic of Ammocryptocharax species.

The species of Characidium, as the genus is currently defined (Buckup, 1993a -b), occupy several very distinct niches in tropical fresh waters. All species examined so far feed on aquatic invertebrates, but obtain them from very different habitats. Our typical appreciation of what have been called “South American Darters” applies to many species living in the riffles of Andean mountain streams. C. longum is one of several species that occurs over white sand beaches in lowland habitats with low sediment loads, strong flow, and tea-colored waters. Still others live in sluggish savannah streams, amongst aquatic vegetation.