A Gram-positive bacterium, designated strain Kis4-19^T, was isolated from the intestinal tract of a fish, and its taxonomic position was investigated by a polyphasic approach. The cells of strain Kis4-19^T were coccus-shaped, non-motile and non-sporulating. The peptidoglycan type of this organism was A3γ; LL-diaminopimeric acid (LL-A₂pm) was the diagnostic diamino acid of the peptidoglycan. The predominant menaquinone was MK-8(H₄), and the major fatty acids were iso-C_15:0, iso-C_14:0 and iso-C_16:0. Galactose was detected as a cell-wall sugar. The polar lipids were diphosphatidylglycerol, phosphatidylglycerol, phosphatidylinositol and lyso-phosphatidylethanolamine. The DNA G+C content was 71.1 mol%. Sequencing analysis of the 16S rRNA gene indicated that strain Kis4-19^T was closely related to Arsenicicoccus bolidensis CCUG 47306^T (97.5%). However, DNA–DNA hybridization results and phenotypic characteristics revealed that the strain Kis4-19^T differed from A. bolidensis. Therefore, strain Kis4-19^T represents a novel species of the genus Arsenicicoccus, for which the name Arsenicicoccus piscis sp. nov. is proposed. The type strain is Kis4-19^T (=NBRC 105830^T =DSM 22760^T).