A major food web component in the orinoco river channel: evidence from planktivorous electric fishes.

Deep-water sampling of the Orinoco River main channel resulted in the collection of an unexpectedly high abundance and diversity of specialized fishes. Twenty-eight of the more than 60 species collected belong to the Gymnotiformes(New World electric or knife fishes). One of the more numerous of these, a recently described species of the genus Rhabdolichops, consumes large numbers of very small planktonic Crustacea and insect larvae. These items are captured in the very swift, turbid, and deep waters of the Orinoco. Although the strong dependence of the river food web on terrestrial and floodplain food sources is well known, the specialized capabilities of Rhabdolichops and of other fishes that occur with it indicate a significant extension of the river food web into the main channel.