Family Gymnotidae Rafinesque 1815 (Fig. 3C). Gymnotids, Nakedback Knifefishes, Gymnotid Eels; Peces Cuchillo, Anguilas, Machetes

Description: Body elongate, strongly compressed to subcylindrical; usually less than 30 cm in length; mouth superior, lower jaw protruding; eyes very small; scales present, small; pelvic and dorsal fins absent; anal fin terminating at a point near the tip of the tail; usually brown in color (Bussing 1998, Angulo et al. 2021, Nelson et al. 2016). Distribution: Freshwater; North (southern Mexico only), Central and South America (Nelson et al. 2016). One genus and two species in Nicaraguan freshwaters.