Gymnotus choco, James S. Albert & William G. R. Crampton, 2003

James S. Albert & William G. R. Crampton, 2003, Seven new species of the Neotropical electric fish Gymnotus (Teleostei, Gymnotiformes) with a redescription of G. carapo (Linnaeus)., Zootaxa 287, pp. 1-54 : 26-29

Gymnotus choco n. sp. Albert, Crampton, and Maldonado

(Fig. 3, Tables 2 and 3)

Holotype: ICNMHN 6621, 237 mm, collected 28 February 1993, at Boca de Pepé, Río Baudó, Chocó Department, Colombia (05°03'N, 77°03'W) by S. Kullander and A. Silfvergrip.

Paratypes: NRM 27734 (6), 142-260 mm. Collected with holotype.

Nontypes: 7 lots with 14 specimens, all collected in Colombia. CAS 72192 (2), 150- 179 mm, 1913, Río Sucio, Río Truando, Chocó Department, Atrato basin (07°09'N, 77°12'W). ICNMHN 6686 (1), 321 mm, March 1994, Upper Río San Juan, Pueblo Rico, Risaralda Department. IMCN 1050 (2), 208-239 mm, June 01, 2002, Resguardo Puerto Pizarro, Río San Juan, Litoral del San Juan, Chocó Department. IMCN 1370 (1), 215 mm, same collection data as IMCN 1050. FMNH 70511 (5), 124-247 mm, November 1945, at Pizarro (Baja Baudó), Río Baudó, Chocó Department (04°58'N, 77°22'W). FMNH 56794 (2), 174-175 mm, same collection data as CAS 72192. NRM 27744 (1), 350 mm, 07 February1989, at Quebrada Piscindé, close to Pan-American bridge across Río San Pablo, Atrato basin, Chocó Department (05°42'N, 76°37'W).

Diagnosis. Gymnotus choco can be distinguished from other species of the G. carapo species-group by a color pattern with obliquely oriented pale-yellow bands in which the band-interband margins are irregular and wavy, in which there are one to three inverted Y- shaped (divided ventrally) dark bands in the posterior portion of body (at bands 6-9 from posterior tip of tail), and in which the pale bands do not extend above the lateral line on the anterior 2/3 of body. Gymnotus choco is most similar to G. paraguensis n. sp. (described below) from the Pantanal of Brazil and Paraguay from which it can be distinguished by: 1, a more narrow mouth (MW 28.3-29.7% HL [mean 33%, n=9] vs. 38.6-39.0% [mean 39%, n=4]); 2, a more cylindrical body (BW 0.68-0.83% BD [mean 77%, n=9] vs. 0.60-0.69 [mean 66%, n=4]); 3, a longer preanal distance (PA 76.7-90.7% HL [mean 84%, n=9 vs. 62.9-81.2% [mean 69%, n=4]). Gymnotus choco can be further distinguished from other taxa of the G. carapo species-group by the unique combination of character states provided in Table 4.

Description. Fig. 3 illustrates head and body shape and pigment patterns. Morphometric data in Table 2, and meristic data in Table 3. Body size moderate, up to 260 mm. Size at reproductive maturity and sexual dimorphism unknown. Scales circular or slightly ovoid, present on entire post-cranial portion of body from nape to caudal appendage. Gape size in mature specimens large, extending to or beyond posterior nares. Mouth position superior, lower jaw longer than upper, rictus decurved. Chin fleshy and bulbous. Anterior narial pore partially or entirely included within gape in large narial fold. Anterior nares large, subequal to diameter of eye. Mesethmoid anterior margin concave with short paired anterolateral processes. Mesethmoid neck broad, more than width of ventral ethmoid. Ethmoid region between anterior nares broad, its anterior margin rounded. Circumorbital series ovoid. Eye position lateral, lower margin of eye dorsal to rictus.

Premaxilla with 13-15 teeth disposed in single row along outer margin, arrow-head shaped anteriorly, conical posteriorly. Median margin of premaxilla curved. Maxillapalatine articulation near anterior tip of mesopterygoid. Maxilla orientation vertical. Maxilla rod-shaped, narrow distally with straight ventral margin. Maxilla length equal to about width of 4-6 dentary teeth. Dentary with one row of 16-17 teeth (n=2), 2-3 arrow-shaped teeth anteriorly, all others conical posteriorly. Dorsoposterior and ventroposterior dentary processes abut at midlength of dentary. Dentary ventroposterior process almost as long as dorsoposterior process. Dentary dorsoposterior process narrow distally. Dentary ventral margin with a narrow lamella, less than posterior process. Anteroventral margin of dentary rounded in lateral view, without a hook. Dorsal margin of opercle straight or slightly convex. Texture of dorsal opercle process deeply pitted and cancellous. Dorsal opercular crest longer than dorsal opercle process. Posterior margin of opercle smooth, entire, without spines or processes. Ventral ridge field of opercle broad. Dorsal ridge field of opercle long, more than half width of opercle. Dorsoposterior laterosensory ramus of preopercle with two superficial pores. Preopercle with anteroventral notch. Margin of preopercular medial shelf entire. Median shelf of preopercle small, less than half width of symplectic. Ascending process of mesopterygoid robust, long, its base shorter than its length. Mesopterygoid ascending process curved. Tip of mesopterygoid ascending process simple. Metapterygoid superior and inferior portions approximately equal in size. Dorsal margin of interopercle with broad ascending process. Dorsal margin of subopercle concave. Posterior margin of retroarticular square. Retroarticular with an arched lamella posteriorly, forming a small canal. Anguloarticular process short, to ventral margin poster. Mandible long, extended, its length more than twice its depth. Trigeminal canals (supraorbital, infraorbitral) with separate fenestrae on outer surface of hyomandibula. Posterior lateral line fenestra contacting dorsoposterior margin of hyomandibula. Cranial fontanels closed in juveniles and adults. Anterior margin of frontal straight, continuous with margins of adjacent roofing bones. Frontal postorbital process broad, more than two times width of supraorbital canal. Frontal shape narrow, width at fourth infraorbital less than that of parietal. Lateral ethmoid absent. Parasphenoid posterior process broad. Parasphenoid lateral process broad, triangular. Parietal rectangular, its length less than width. Pterosphenoid anteroventral portion robust, extending ventral to lateral margin of parasphenoid. Prootic foramen Vp combined with V2-3+VII. Adductor mandibula undivided at insertion. Adductor mandibula intermusculars absent. All basibranchials unossified. Gill rakers not contacting gill bar. Basibranchial 5 unossified. Pectoral medial radial large. Mesocoracoid elongate, its length more than 4 times width. Postcleithrum thin, discoid or sickle-shaped. Cleithrum narrow, with a straight ventral margin. Anterior limb of cleithrum long, more than 1.8 times ascending limb. Cleithrum deeply incised on its anteroventral margin. Cleithrum without large facet for insertion of muscle from supracleithrum. Rib 5 robust along its entire extent, less than 3 times width of rib 6. Hemal spines present. Displaced hemal spines absent. Multiple anal-fin ray branching posterior to rays 10-17. Length anal-fin pterygiophores equal to or longer than hemal spines. Single hypaxial electric organ, extending along entire ventral margin of body. Electric organ discharge not known.

Color in alcohol. Ground color of body dark brown dorsally grading to pale brown ventrally. Chromatophores most densely concentrated along dorsum near midline. Body with 21 or 22 (median 21) obliquely oriented pale-yellow bands on ventrolateral surface extending from tip of tail to pectoral-fin base. Band appearance variable in shape, width, and arrangement, both on and among individuals. Band-interband margins irregular and wavy. One to three inverted Y-shaped (divided ventrally) dark bands in posterior portion of body, at bands 6-9 from posterior tip of tail. Pale bands do not extend above lateral line along anterior 2/3 of body. Interband contrast increases ventrally and caudally, and more pronounced in smaller specimens. Anterior 80% of dorsum (anterior to anal-fin clear patch) without banding. Three bands from either side meet on ventral midline, between anus and anal-fin origin. A single band posterior to last anal-fin ray.

Head not banded, its ground color dark brown dorsally grading to lighter brown ventrally, without freckles and with numerous speckles distributed over branchiostegal membranes and ventral surface of head. Pectoral-fin rays brown, interradial membranes hyaline. Anal-fin membrane divided into three parts along body axis: anterior 40% brown, mid 40% black, posterior 20% translucent.

Distribution. Known from the Río Baudó drainage on the Pacific Slope of Colombia, and the Río Atrato, a Caribbean drainage in northern Colombia (Fig. 4).

Common name. Cuchillo.

Etymology. Specific epithet for the Chocó region on the Pacific slope of Colombia. A noun in apposition.