The large variety of species may be explained by the fact that some 6,000 years ago, the Kapuas River, as a tributary of the Sunda River, was connected to other tributary rivers of South Sumatra, Java and Malay Peninsula. Apart from fish, there are numerous crabs, prawns, water striders and other aquatic insects.[20] The rich flora and fauna results in very complex food chains, with fishes consuming foods ranging from fruits to other fish. For example, Hemirhamphodon pogonognathus feeds exclusively on terrestrial insects.