Gymnotus esmeraldas, 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 : 30-32

Gymnotus esmeraldas n. sp. Albert and Crampton

(Fig. 5, Tables 2 and 3)

Holotype: MCZ 58729, 296 mm, collected 18 June, 1977, at Hoja Blanca nr. San Miguel, Ríos Cayapas, Río Esmeraldas drainage, Ecuador (01°05'N, 79°03'W) by K. Miyata and A. Rankis.

Paratypes: MCZ 162745 (4), 200-309 mm; collected with holotype.

Nontypes: 2 lots with 3 specimens, all collected in Ecuador. CAS 164103 (1), 355 mm, 01 December, 1949, nr. mouth of Río Quinide, Río Toachi, Río Blanco, Río Esmeraldas drainage. FMNH 92041 (2), 229-288 mm, 31 July, 1974 nr. Station 16, Río Palenque Biological Station, Los Rios Department, Río Guayaquil drainage.

Diagnosis. Gymnotus esmeraldas can be distinguished from all species of the G. carapo species-group except G. bahianus by the absence of alternating dark and light pigment bands on the anterior 80% of the body. Specimens in the type series of G. esmeraldas from the Río Esmeraldas basin possess a unique speckled color pattern composed of irregular pale yellow or cream-colored patches interspersed on a dark brown ground color over most body and anal-fin surfaces, in which the pale pigment patches are about 2-3 scales in width and height. Gymnotus esmeraldas is most similar to G. henni n. sp. (see below) from the Río Calima on the Pacific Slope of Colombia, from which it can be distinguished by: 1, reticulated color pattern without bands on the majority of the body surface and without pale blotches on the head (vs. presence of 13-16 pigment bands and pale blotches on the head]; 2, body shape laterally compressed (BW 58-77% BD [mean 69%, n=8] vs. 77-87% [mean 80%, n=7]); 3, moderate number of pored lateral-line scales to first ventral ramus (PLR 51-54 [median 52, n=8] vs. 59-68 [median 62, n=7]). In addition to color differences, G. esmeraldas can be distinguished from G.bahianus by: 1, a more slender body (BD 8.2-9.8% HL [mean 8.8%, n=8] vs. 9.3-13.3% [mean 11.1, n=21]); 2, more pectoralfin rays (P1R 17-19 [mode 17, n=8] vs. 15-16 [mode 16, n=6]); 3, a longer preanal region (PA 82-98% HL [mean 92%, n=8] vs. 76-97% [mean 85%, n=22]); 4, elongate (vs. circular) scales (SAL 8-9 [mode 8, n=8] vs. 6-7 [mode 7, n=16]); and 5, broader electric organ with more rows of electroplates (CEP 4-5 [mode 5, n=8] vs. 3-4 [mode 4, n=6]). Gymnotus esmeraldas can further be distinguished from congeners by the unique combination of character states provided in Table 4.

Description. Fig. 5 illustrates head and body shape and pigment patterns. Morphometric data in Table 2 and meristic data in Table 3. Size up to 309 mm. Size at reproductive maturity and sexual dimorphism unknown. Scales present on entire post-cranial portion of body from nape to caudal appendage. Scales above lateral line large, 8-9 to dorsal midline at midbody. Most scales on body moderately elongate, scales above lateral line at midbody approximately 2-3 times as long as deep, their proportional elongation increasing with body size. Gape size in mature specimens large, extending to or beyond posterior nares. Mouth position superior, rictus decurved. Eye position below horizontal with front of mouth. Anterior narial pore partially or entirely included within gape. Circumorbital series ovoid. Caudal appendage short, less 0.5 times length of pectoral fin. Single hypaxial electric organ, extending along entire ventral margin of body. Electric organ discharge not known. Many osteological features not known due to paucity of specimens for clearing and staining; some character states were determined from radiographs. Dorsoposterior laterosensory ramus of preopercle with two superficial pores. Displaced hemal spines absent. Multiple anal-fin ray branching posterior to rays 10-17. Length of anal-fin pterygiophores equal to or longer than hemal spines.

Color in alcohol. Ground color of body pale brown with slight countershading, and chromatophores concentrated along dorsum near midline. Body with 6-10 very irregular dark bands with wavy margins or broken to blotches restricted to the posterior 20% of body. Pigment bands not apparent on anterior 80% of post-cranial body, coloration composed here of irregularly distributed pigment patches in a reticulate pattern of cream-colored and dark brown areas over body and anal-fin surfaces. Pigment patches about 2-4 scale-diameters across, with dark and light patches summing to approximately equal total surface areas in region over hypaxial musculature.

Head ground-color dark chocolate dorsally, without blotches, pale yellow ventrally. Dark regions on dorsal surface of head composed of numerous dark brown chromatophores with even pigment densities. Branchiostegal membranes and ventral surface of head almost without pigments. Pectoral-fin interradial membranes dusky or hyaline. Color of anal-fin membrane graded along body axis, from light brown or hyaline anteriorly to dark brown or black posteriorly, with short, obliquely oriented hyaline and dark stripes near fin base in posterior-most region.

Distribution. Known from two river basins on Pacific Slope of Ecuador; the Río Esmeraldas and Río Palenqué, Guayaquil basin (Fig. 4).

Common name. Unknown.

Etymology. Specific epithet in allusion to the Río Esmeraldas. A noun in apposition.

Remarks. Specimens referred to G. esmeraldas from the Río Guayaquil basin are uniformly dark brown (without speckles or reticulated pattern).