A New Species of Gymnotus (Gymnotiformes, Gymnotidae) from Uruguay: Description of a Model Species in Neurophysiological Research
Gymnotus omarorum is described from coastal and interior drainages of Uruguay, where it is locally abundant in streams and lagoons, and is not known to occur sympatrically with congeners. This species has been used for more than 30 years as a model organism in neurophysiological research, where it has been referred to as G. carapo or G. cf. carapo. Gymnotus omarorum is a member of the G. carapo species group, with which it shares the presence of two pores in the dorsolateral portion of the preopercle, irregular (wavy) dark pigment bands which usually become broken and/or lose contrast with the ground color through growth, a clear patch at the caudal end of an otherwise darkly pigmented anal fin, and more than four arrowhead-shaped (anteroposteriorly compressed) teeth in the anterior portion of the dentary. Gymnotus omarorum is readily differentiated from other members of the G. carapo species group by the following unique combination of character states: a short distance to first ventral lateral-line ramus (39–45% TL vs. 47–58%), few pored scales to first ventral ramus (27–35 vs. 40–78), many ventral lateral line rami (16–37 vs. 0–14), and ovoid (vs. elongate) scales on the posterior portion of body.Abstract
Gymnotus omarorum head and body, ZVC-P 6480, holotype, 254 mm, Laguna del Sauce, Uruguay, 34°50.328′S, 055°06.869′W. Scale bars = 20 mm.
Electric Organ Discharge (EOD) waveform (above) and Fourier Power Spectrum (below) for (A) 30 juvenile and adult specimens (120–262 mm) of Gymnotus omarorum from the type locality (all undamaged specimens; AMNH 239656, ZVC-P 6480, ZVC-P 6481). (B) 14 post-larval specimens (24–32 mm) from the type locality (all undamaged specimens; AMNH 239656, ZVC-P 6481). EODs plotted with head positivity upwards, normalized to the amplitude of the dominant positive phase (P1), and aligned at the P1 peak. Scale bar = 1 msec. Black labels P1–P3 refer to EOD phase 1–3 (Crampton et al., 2005). Gray labels V1–V4 refer to phase labeling scheme used by the Montevideo research group (Caputi, 1999).
Map of Rio Uruguay and portions of adjacent river basins showing the known geographic distribution of Gymnotus omarorum. Square indicates the type locality. Symbols may represent more than one locality. Scale bar = 100 km.
Contributor Notes
Associate Editor: C. J. Ferraris.