FEEDING OF A BENTHIC GOBY IN A RIVER WHERE NEKTONIC FISHES ARE ABSENT

The social structure and feeding behaviour of the benthic goby Rhinogo bius sp. DA (dark type) were investigated in a small river in Shikoku, Japan, where nektonic fishes are absent. The gobies had overlapped ho me ranges but were often aggressive against conspecifics, especially o f the same sex and similar body size. Their diet consisted mainly of a quatic invertebrates, but terrestrial invertebrates were also an impor tant item. This contrasted with few terrestrial invertebrates in the d iet of the conspecifics in an adjacent river harbouring a nektonic cyp rinid fish. An increase in flow level greatly changed their feeding be haviour; on high flow days, a greater portion of the population appear ed from the interstices of the bottom and more often rose into the wat er column to catch drift than on normal flow days. Plasticity of their feeding behaviour is discussed in terms of ecological release.