Feeding dynamics of Rhaphiodon vulpinus Agassiz, 1829 (Teleostei, Cynodontidae) in the upper Tocantins River (GO, Brazil) relative to the impoundment by the Serra da Mesa hydroelectric dam

Abstract

The diet and feeding activity of Rhaphiodon vulpinus were studied before and after the impoundment of the upper Tocantins river by the Serra da Mesa hydroelectric plant (Goiás State, central Brazil), in two areas: reservoir and downstream. Stomach contents of 214 specimens were analyzed: 46 from the river phase (Dec./95 to Oct./96), 100 from the filling phase (Dec./96 to Apr./98) and 68 from the operation phase (Jun./98 to Feb./00). The species was confirmed as a piscivore, with occasional consumption of insects and vegetal material. In the downstream area, none of the identified prey was common to all the three phases. The most consumed prey were Geophagus cf. surinamensis, Hemiodus ternetzi and Pimelodus blochii during the river, filling and operation phases, respectively. The engraulid Anchoviella sp. was exclusive to the operation phase. Prey richness was higher in the reservoir. Small-sized characids were consumed during the three phases, whereas H. ternetzi, Leporinus friderici and Tetragonopterus argenteus were exclusive to the river phase, Ctenobrycon hauxwellianus and Pimelodidae to the filling phase, and Satanoperca aff. jurupari to the operation phase, the latter being the most important in this phase. The feeding activity, given by the proportion of stomachs with food (EcA%) and empty (EV%), increased in each phase in the downstream area. In the reservoir, the opposite pattern was observed. No correlation was found between the sizes of predator and its prey; however, larger predators consumed prey of a wide size range.