Two Gram-positive bacteria, designated strains Aji5-31^T and Ngc37-23^T, were isolated from the intestinal tracts of fishes. 16S rRNA gene sequence analysis indicated that both strains were related to the members of the family Dermatophilaceae, with 95.6-96.9% 16S rRNA gene sequence similarities. The family Dermatophilaceae contains 2 genera and 3 species: Dermatophilus congolensis, Dermatophilus chelonae and Kineosphaera limosa. However, it has been suggested that the taxonomic position of D. chelonae should be reinvestigated using a polyphasic approach, because the chemotaxonomic characteristics are not known (Stackebrandt, 2006; Stackebrandt and Schumann, 2000). Our present study revealed that strains Aji5-31^T, Ngc37-23^T and D. chelonae NBRC 105200^T should be separated from the other members of the family Dermatophilaceae on the basis of the following characteristics: the predominant menaquinone of strain Aji5-31^T is MK-8(H₂), strain Ngc37-23^T possesses iso- branched fatty acids as major components, and the menaquinone composition of D. chelonae is MK-8(H₄), MK-8 and MK-8(H₂) (5 : 3 : 2, respectively). On the basis of these distinctive phenotypic characteristics and phylogenetic analysis results, it is proposed that strains Aji5-31^T and Ngc37-23^T be classified as two novel genera and species of the family Dermatophilaceae. The names are Mobilicoccus pelagius gen. nov., sp. nov. and Piscicoccus intestinalis gen. nov., sp. nov., and the type strains are Aji5-31^T (=NBRC 104925^T =DSM 22762^T) and Ngc37-23^T (=NBRC 104926^T =DSM 22761^T), respectively. In addition, D. chelonae should be reassigned to a new genus of the family Dermatophilaceae with the name Austwickia chelonae gen. nov., comb. nov.