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The purpose of this study was to estimate the genetic distance, diversity and relationship of two large groups of Malawian cichlid, 'mbuna' living in rocky area and feeding on algae, and 'non-mbuna' in sandy area feeding on various items. A total of 78 species from 42 genera was determined for the DNA sequence of the mitochondrial control region. In a genetic tree, constructed with Kimura-2 parameter as a distance by NJ method, mbuna created only one group whereas non-mbuna created four groups by a single or multiple genera. Some genera, such as Campsochromis and Labeotropheus with no genetic diversity within genus constructed a small congeneric clade, suggesting genetic homogeneity. In contrast, some genera, such as Otopharynx and Placidochromis with a high genetic diversity, participated in multiple groups including mbuna and nonmbuna, suggesting genetic heterogeneity. The largest Group A, exclusively composed by non-mbuna, showed an apparently high average genetic distance whereas Group D, in which all mbuna participated, showed an apparently low average genetic distance. It was suggested that non-mbuna have attained much higher diversification than mbuna. This different diversification may partly be attributable to sexual selection strongly exerted in rocky habitats in contrast to strong ecological selection in sandy area.

A new species of the genus Tanytarsus van der Wulp, 1874 was described and illustrated based on an adult male. Tanytarsus trichovalis sp. nov. belongs to the eminulus species group, and is closely related to T. tamaundecimus Sasa, 1980, T. okuboi Sasa, 1986, and T. tonebeceus Sasa & Tanaka, 2000. However, the species is distinguished from these species by the morphology of the hypopygium. We also present the first record of T. ovatus Johannsen, 1932 in Japan. In addition, DNA barcoding of 5 species including T. trichovalis sp. nov., T. ovatus, and other morphologically related species was undertaken. A new key of the eleven Japanese eminulus species group was compiled.