Alimentación de Gymnotus omarorum (Gymnotiformes: Gymnotidae) en Laguna Blanca (Parque Nacional Río Pilcomayo), Formosa, Argentina

Abstract

Diet of the electric knife-fishes, Gymnotus omarorum, is described in Laguna Blanca Río Pilcomayo National Park, Formosa province. Samples were collected monthly from September 2012 to July 2013. For the analysis of stomach contents, frequency methods, volume fraction, percentage and numerical abundance index (AI) were used. Preys ingested generally belong to invertebrates and fish that live under the floating plants. The specimens of smaller sizes to 200 mm total length (TL) had a carnivorous diet with greater specialization, while in larger sizes from 201 mm TL, was carnivorous diet of the generalist type. Increased consumption of fish and decapods with increasing LT was observed. Insects in general and in particular Odonata nymphs, dominate in small and medium sizes. Significant differences were observed in the diet of this species throughout the period considered, correlating the same with changes in biomass of floating plants. The results allow characterizing the diet of Gymnotus omarorum as a generalist.