The deep-sea flatfishes Poecilopsetta colorata and P. praelonga (Actinopterygii, Pleuronectiformes, Poecilopsettidae) from the Pacific coast of southern Japan

Poecilopsetta colorata Günther, 1880 and Poecilopsetta praelonga Alcock, 1894, deep-sea flatfishes belonging to the family Poecilopsettidae (Teleostei, Pleuronectiformes), are recorded for the first time from Japan, based on two specimens of the former and one of the latter, all collected from the Pacific coast of southern Japan. The diagnostic characters of each species are reassessed. The former specimens, from the Enshu-nada Sea and Tosa Bay, were identified as P. colorata by a combination of the following characters: dorsal-fin rays 48–62; anal-fin rays 46–53; ocular-side pectoral-fin rays 9–12; lateral-line scales 90–124; body deep; eyes separated by flat scaled interorbital area; middle pectoral-fin rays on ocular side branched; and single large dark blotch on ocular-side pectoral fin.

A second specimen from the Enshu-nada Sea was identified as P. praelonga, having the following diagnostic characters of that species: dorsal-fin rays 57–65; anal-fin rays 45–55; ocular-side pectoral-fin rays 6–11; lateral-line scales 91–111; body slender; eyes contiguous; all pectoral-fin rays simple on both sides; straight section of lateral line about three times length of lateral-line curve width; pectoral fin uniformly black.

The specimens from the Enshu-nada Sea represent the northernmost records for each species, P. colorata and P. praelonga having been previously recorded only as far north as the South China Sea off Hong Kong, and from southern Taiwan, respectively. It is likely that the ocular-side head and body coloration of P. colorata and the caudal-fin coloration of P. praelonga are variable intraspecifically, whereas the presence or absence of branched ocular-side pectoral-fin rays is species-specific in Poecilopsetta.

The presently reported specimens are likely to have been transported by the Kuroshio Current while at the pelagic larval stage, thereafter, settling near their collection sites, due to having remnants of blind-side black spots, which are distinct in larval and juvenile Poecilopsetta, but tend to disappear with growth.