Gymnotus ardilai, Javier A. Maldonado-Ocampo & James S. Albert, 2004

Javier A. Maldonado-Ocampo & James S. Albert, 2004, Gymnotus ardilai: a new species of Neotropical electric fish (Ostariophysi: Gymnotidae) from the Rio Magdalena Basin of Colombia., Zootaxa 759, pp. 1-10 : 5-9

Gymnotus ardilai new species

(Figs. 1-3).

Holotype. - IAvHP 3477 ( CAR 05), 430 mm TL. Female. Colombia, Santander, Girón, Río de Oro, collected by Carlos Ardila, 6 January 2000.

Paratypes. - IAvHP 4001 (2, 219.2-329 mm TL, males). Colombia, Santander, Girón, Río de Oro, collected by Carlos Ardila, 4 January 2004.

Diagnosis. - Gymnotus ardilai differs from all congeners in possessing the following unique combination of characters: 1, a clear patch at the caudal end of the anal fin; 2, two laterosensory canal pores (from the preopercular-mandibular series) in the dorso-posterior portion of the preopercle; 3, progressive loss of alternating dark and light pigment bands with the size, with no pigment bands in individuals more than 350 mm TL (a pattern that is readily distinguishable from all other described species of the G. carapo species-group except populations of G. esmeraldas from the Guayaquil basin); 4, a long head (HL 10.2- 11.2 % TL total length vs. 7.9-11.8 % in all other species except G. carapo and G. arapaima ); 5, many (9-10) scales over anal fin pterygiophores (vs. 4-9 in all other species except G. arapaima ); 6, few (47-48) pored lateral-line scales to first ventral ramus (vs. 32 -38 [median 37] in G. mamiraua , vs. 42-52 [median 48] in G. carapo , and vs. 50-64 in all other species); 7, a low (84 n = 1) total number of pored lateral-line scales (84 n = 1vs. 93 -108 [median 98] in G. carapo , and vs. 106-140 in all other species except G. mamiraua ); and 8, a relatively large eye (orbital diameter 8.5-9.0 % HL vs. 6.0-7.0 % in G. carapo ).

Description. Body shape and pigment patterns illustrated in Figs. 1 and 2. Morphometrics and meristics data for the holotype and paratypes are presented in Tables 2 and 3. Size of maturity and sexual dimorphism unknown. However, the holotype which corresponds to a female, presents a developed gonad that is present in 2/4 of the body and presents a yellow color. Scales cycloid, ovoid, present on entire post-cranial portion of body from nape to tip of caudal appendage. Scales on dorsal surface relatively large at midbody, eight to nine rows from lateral-line to dorsal midline. Scales small over pterygiophores, nine to 10 scale rows. Lateral-line scales approximately 4.3 mm high by 4.0 mm long in humeral region (n = 1); 5.6 mm high by 6.3 mm long at midbody (n = 1); 3 mm high by 3.5 mm long dorsal to anterior margin of clear patch on anal-fin (n = 1). Gape size in mature specimens large, extending beyond posterior nares. Mouth position superior, lower jaw longer than upper, rictus decurved. Chin fleshy and bulbous with thick pad of electroreceptor organs and support tissues overlying tip of snout and oral jaws. Anterior narial pore included within gape in large narial fold. Anterior nares large, subequal to diameter of eye. Branchial opening moderate (31.2-38.8 % HL). Circumorbital series ovoid. Ethmoid region between anterior nares moderate, its anterior margin rounded. Eye position lateral, lower margin of eye slightly ventral to rictus. Eye relatively large, orbital diameter 8.5-9.0 % HL. Premaxilla and dentary with one row of large, slightly recurved, conical teeth. Premaxilla with 14-22 (n = 2) teeth disposed in single row along outer margin. Dentary with 17-26 (n = 3) teeth disposed in single row along outer margin.

Color in life. Head not banded, spotted or blotched, uniformly dark brown but slightly paler in gular region (Fig. 3). Numerous minute chromatophores speckled over branchiostegal membranes and ventral surface of head. Pectoral-fin rays dark brown or black, interradial membranes hyaline. Anal-fin never blotched, spotted or marked. Analfin rays and membrane dark gray or black on anterior 80% of its length, translucent on posterior 20%. Color variation is progressively correlated with size with larger individuals losing the light bands. Juvenals (34 mm TL) with 15-17 thin well-defined pale bands (Fig. 4).

Electric organ discharge. Unknown .

Distribution. Gymnotus ardilai is known only from the Río de Oro, where it meets the Río Lebrija, in the Magdalena Basin, Colombia (Fig. 5).

Habitat and Ecology. The type and only known locality is an Andean whitewater river (c.1000 meters above sea level, 1.5 meters deep) with low flow, low transparency and high sediment load. Gymnotus ardilai is found free swimming along the river margin. The species coexists with Eigenmannia virescens , Pimelodella chagresi , Rhamdia quelen , Chaetostoma thomsoni , Dolicancistrus carnegiei , Geophagus steindachneri , Aequidens pulcher , Creagrutus magdalenae and Poecilia reticulata . The type locality is heavily polluted from effluents of the municipalities of Pie de Cuesta, Floridablanca and Girón. The effect of pollution on the ecology of G. ardilai is unknown, although this species is very rarely collected and presumably present in low population densities. Examination of the stomach content of the Paratype (212.9 mm TL) shows a diet consisting mostly of aquatic invertebrates, especially larval Odonata.

Common name. Lamprea.

Etymology. Specific epithet in honor to Dr. Carlos A. Ardila Rodriguez, President of the Colombian Ichthyological Association (ACICTIOS), who has contributed to the knowledge of Colombian ichthyology.