Apteronotus eschmeyeri, Carlos David de Santana, Javier A. Maldonado-Ocampo, William Severi & George Nilson Mendes, 2004

Carlos David de Santana, Javier A. Maldonado-Ocampo, William Severi & George Nilson Mendes, 2004, Apteronotus eschmeyeri, a new species of ghost knifefish from the Magdalena Basin, Colombia (Gymnotiformes: Apteronotidae)., Zootaxa 410, pp. 1-11 : 3-9

Apteronotus eschmeyeri new species

Figs. 1-2; Table 1

Sternarchus rostratus . Eigenmann and Fisher (1914): 236 [listed in part]. Eigenmann (1922): plate XXXIV, fig. 5 and plate XXXV, fig. 3.

Apteronotus rostratus . Dahl (1971): 99, illustrated. Albert (2001): 110 [listed in part].

Holotype. CAS 72115 (IU 13377), 303.7 mm, male. Colombia, Departamento Cundinamarca, Rio Magdalena Basin, Las Juntas de Apulo, Rio Bogotá along railway between Girardot and Facatativa. Collected by M. Gonzales, 1913.

Paratypes. FMNH 56775, (2, 195.3-213.6 mm), Colombia, at Girardot, C. H. Eigenmann, 01.02.1912. FMNH 56776, (1, 202.9 mm), Colombia, at Apulo, M. Gonzales. ICN-MHN 6741, (3, 191.0-233.1 mm), Colombia, at Honda, J. A. Maldonado-Ocampo, 2003. IAVHP 3304, (8, 158.7-286.3 mm), Colombia, at Honda, J. A. Maldonado-Ocampo, 2003. IMCN 2000, (3, 190.6-234.8 mm), Colombia, at Honda, J. A. Maldonado-Ocampo, 2003. USNM 120473, (1, 270.9 mm), Colombia, Rio Luisa, N. Maria.

Diagnosis. Apteronotus eschmeyeri is included in Apteronotidae by the presence of a dorsal mid-saggital electroreceptororgan (dorsal thong of Mago-Leccia, 1994; dorsal organ of Albert, 2001) and a caudal fin (Mago-Leccia, 1994; Albert & Campos-da-Paz, 1998; Albert, 2001). The new species shares the following diagnostic features within the subfamily Apteronotinae (Albert & Campos-da-Paz, 1998; Albert, 2001): gape of mouth large, extending to edge of eyes; maxilla rhomboid in lateral view; anterior surface of mesethmoid concave and lateral process of ventral ethmoid robust (Albert, 2001). Apteronotus eschmeyeri was included in Apteronotus by the presence of two of five synapomorphies proposed by Albert (2001): body surface deep brown or black with a white middorsal stripe and white mental and caudal patches, and elongate posterior limb of anguloarticular. The new species can not be included in any previous species-group proposed by Albert (2001).

Apteronotus eschmeyeri can be distinguished from congeners by the following combination of features: 1, blotchy coloration on body (vs. even brown or black coloration in most Apteronotus , except A. cuchillo and A. magdalenensis , which have blotchy or marble coloration); 2, clear band from chin to the beginning of dorsal mid-saggital electroreceptororgan (vs. uniform coloration in A. brasiliensis , A. ellisi , A. jurubidae , A. magdalenensis , and A. marauna ); 3, two clear bands surrounding the caudal peduncle in specimens up to 165 mm TL; bands become obscured by pigment blotching in specimens larger than 165 mm (vs. two clear bands encircling the caudal peduncle throughout development in A. albifrons and A. caudimaculosus ; one clear band surrounding the base of caudal fin throughout development in other species of Apteronotus , with exception of A. magdalenensis and A. cuchillo ); 4, mouth rictus extends to beyond the posterior margin of eyes (vs. mouth rictus anterior to posterior margin of eyes in A. cuchillo , A. magdalenensis , and A. marauna ).

Description. Morphometrics for holotype and paratypes are presented in Table 1. Body proportions and pigmentation are illustrated in Figs. 1 and 2. Body laterally compressed, with greatest body depth at abdominal cavity or just posterior to this region. Dorsal profile straight. Lateral line extending to tail, absent on caudal fin. First perforated scale above pectoral-fin origin.

Head laterally compressed, widest at opercular region and deepest at dorsal region; bones of cranium not reticulated. Head profile straight in males and slightly convex in females. Snout straight and long in males, slightly convex in females. Mesethmoid short and narrow, its anterior tip reduced, flexed ventrally, and concave. Lateral ethmoid present, ossified, small and slender, shaped as a tube. Eyes small, laterally situated on head, completely covered by thin membrane. Premaxilla of moderate size, bearing two irregular rows of teeth, with 10 to 11 conical teeth. Maxilla crescent-shaped, with ossified anterodorsal head and anteroventral shelf; ventral margin of its descending blade curved. Dentary longer than deep, with three to four irregular rows of teeth. Anguloarticular elongated. Mouth large, terminal, rictus passing the vertical through posterior border of eyes in both sexes. Jaws equal; lower lip fleshy. Endopterygoid narrow, without teeth, with ascending process connecting the orbitosphenoid, its base ossified; anterior portion narrow, extending to midlength of dentary. Metapterygoid triangular, posterior portion an ascending process. Sympletic shorter than hyomandibula and articulated with it by a cartilage. Four branchiostegal rays, first and second almost filamentous, the remaining large and laminar. Anterior nares at end of small tube, close to tip of snout; posterior nares ellipsoid, without tube, closer to tip of snout than to eyes. Branchial opening anterior to pectoral fin origin; branchial membranes joined to isthmus. Anus and urogenital papilla adjacent, located in a vertical posterior to eyes, but without a noticeable forward displacement with age. Pectoral fin somewhat elongated, broad and pointed distally, with ii-iii + 15 (iii + 15). Origin of anal fin slightly anterior to opercular region; anal fin rays 160-175 (167) (n = 19, mode = 171), with the 23 (n = 1, holotype) anterior ones unbranched. Small cycloid scales covering body, with 11 to 14 (n = 5, mode = 11) rows above lateral line. Precaudal vertebrae 16-18 (n = 2), first four as transition vertebrae; total vertebrae 77 (n = 1, holotype). Dorsal mid-saggital electroreceptororgan origin on posterior half of body, and inserted into narrow middorsal groove, almost extending to, or slightly passing, end of anal fin. Caudal appendage compressed and short, ending in a small and elongated caudal fin, with 20-22 rays (20) (n =15, mode = 22).

Coloration in alcohol. Body brown with dark spots. Pectoral and anal fins brown, caudal fin with dark spots. Clear band from chin to beginning of dorsal mid-saggital electroreceptororgan. Two clear bands surrounding caudal peduncle in specimens to 165 mm TL, which become obscured by pigment blotching in specimens larger than 165 mm.

Distribution. Apteronotus eschmeyeri is known from the Magdalena Basin, the Rio Bogotá and Rio Luisa in Colombia (Fig. 3), and inhabits slow-flowing waters (Fig. 4) (Dahl, 1971; Maldonado-Ocampo & Albert, in press). In a current review of Colombian gymnotiforms, JAM found individuals reported only from the Honda locality. Apteronotus eschmeyeri occurs in sympatry with A. magdalenensis , A. mariae and A. rostratus .

Etymology. The name eschmeyeri is in honor of William N. Eschmeyer of the California Academy of Sciences, who greatly contributed to ichthyology with his "Catalog of Fishes".

Local Names. Common local names for A. eschmeyeri in Colombia are: "mayupa negra" and "mayupa".

Dahl (1971) reports that A. eschmeyeri is eaten by native people. However, in a recent survey to the Magdalena Basin, JAM talked with local fishermen in Honda, and they did not report any commercial use for this species. It is accidentally captured with gills nets used for commercial fishes (e.g., Prochilodus magdalenae ), but then is returned to the water.

Size and sexual dimorphism. We examined specimens of A. eschmeyeri up to a maximum size of 303.7 mm (male). Dahl (1971) reported a maximum size of 400.0 mm for this species. It is possible that this species shows secondary sexual dimorphism with relation to head morphology. Sexual dimorphism in head morphology has been reported in several apteronotid species (Cox-Fernandes, 1998; Cox-Fernandes et al., 2002; de Santana, 2003). However, the small number of specimens of A. eschmeyeri does not allow a more detailed analysis of sexual dimorphism.

Discussion. Although previously identified as A. rostratus by Eigenmann & Fisher (1914), Eigenmann (1922), Dahl (1971) and Albert (2001), A. eschmeyeri can be distinguished from A. rostratus by the following characters: body coloration blotchy in adults vs. even brown to black, two clear bands surrounding the caudal peduncle in specimens up to 165 mm TL (i.e., clear bands at caudal peduncle that become obscured by dark blotching in specimens larger than 165 mm) vs. clear band at caudal fin base, maxilla without an ascending process in the dorsoposterior portion vs. maxilla with one conspicuous ascending process in the dorsoposterior region, lateral ethmoid ossified vs. lateral ethmoid absent or unossified. The new taxon can be distinguished from A. mariae by the body having blotchy coloration vs. body coloration finely spotted, lateral ethmoid ossified vs. lateral ethmoid absent or unossified. It is distinguished from A. magdalenensis by having the sphenoid region of neurocranium less than one-third total head length in mature specimens, combined axial length of orbitosphenoid and pterosphenoid about equal to length of preorbital region, vs. sphenoid region of neurocranium more than one-third total head length, combined axial length of the orbitosphenoid and pterosphenoid bones greater than preorbital region, orbit positioned at anterior third of head (e.g., Albert, 2001: 26, fig. 15).

Recent collecting efforts and the examination of material deposited in Colombian fish collections failed to show the presence of A. eschmeyeri at the type locality, but we suspect that this species is present in other locations downstream of the type locality. Further collections will be necessary to locate extant populations. The most probable explanation for the apparent absence of A. eschmeyeri at its type locality is due to the influence of highly polluted waters from the Bogota River. The description of a new species endemic species from the Magdalena Basin, five decades after the last apteronotid description from this Basin, reinforces the importance of continuing taxonomic work at the species level and demonstrates that Trans-Andean Apteronotus may be more diverse than previously supposed. The phylogenetic relationship of the new species within the genus is under study and will be addressed in subsequent papers.

Comparative material examined

Remarks on type series. The original lot IUM 13377/ 5596a CM was divided into two and deposited as CAS 72115 (1) and FMNH 56776 (1). Both of these specimens are illustrated in Eigenmann (1922) and identified as Sternarchus rostratus .