Comparative feeding of the relict fish Gymnocharacinus Bergi, a characidae from Southern South America

Abstract

A food analysis was performed of the southernmost distributed Characidae, Gymnocharacinus bergi, the single species inhabiting the thermal headwaters of the Valcheta Creek in northern Patagonia. Chrysophyta were the dominant algae and chironomid larvae and testaceous amoebae the most abundant animal items. Few cladocerans and no copepods were consumed. The diet indicates a benthic feeding habit, though the species usually swims in the water column. Diversity and number of all items are more restricted than those of similar size characids from middle Argentina. The diet of G. bergi is similar to that of Cheirodon interruptus and Bryconamericus iheringi from mountain oligotrophic streams, but differs from tetragonopterine species occurring in richer plain habitats. Feeding traits appear to be related to the environment oligotrophy and agree with regressive traits in the species morphology, presumably associated with harsh environmental pressure. Figure 2 Argentinean “pampa” (northward of the Colorado River) and north of Patagonia (southward).

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