Rhinogobius brunneus (=R. similis) is a common freshwater goby in Japan. Recently, from their colour patterns, these amphidromous fishes have been divided into four types, namely, Cobalt type, Large-black type, Black type and Cross-band type, out of which at least latter three types were once described as a different species. As our second report dealing with the problem of the speciation of these four types, this paper deals with the distribution of these sympatric populations in two small streams. The detailed examination revealed that they clearly segregated as for their longitudinal distributions, or, in the case of co-existence in the same reaches, as for their habitats in relation to river-bed type as well as to flow velocity. By scrutinizing the scattered informations on the distribution of these four types of R. brunneus and its congeneric species, the habitat segregation of these four types was concluded to be not a selective but a interactive one, and that the typical pattern of the habitat segregation in one stream among Japanese freshwater gobies of the Genus Rhinogobius was schematized.
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