Nesting and Paternal Care in the Weakly Electric Fish Gymnotus (Gymnotiformes: Gymnotidae) with Descriptions of Larval and Adult Electric Organ Discharges of Two Species

Abstract

Abstract We describe nesting and paternal care in two species of the weakly electric fish, Gymnotus: Gymnotus carapo from savanna swamps on the Caribbean island of Trinidad; and Gymnotus mamiraua from whitewater floodplains of the Amazon Basin. In both species, single adult males guard eggs and juveniles. Male G. carapo excavate depressions in the substrate or nest in the roots of aquatic macrophytes. Male G. mamiraua form nests exclusively in the root mass of floating meadows of macrophytes. Twelve nests of G. mamiraua were encountered, containing juveniles up to a maximum total length (TL) of 67 mm and estimated maximum age of 8–12 weeks. Two of these nests exhibit a bimodal size distribution, implying more than one spawning event. Juveniles remain close to the male during the day and disperse little more than 1 m away at night. Larval G. carapo and G. mamiraua (approximately 15– 20 mm TL) generate a characteristic Electric Organ Discharge (EOD) with a dominant positive phase followed by a very weak neg...