Ichthyological Research

A new dextral flounder, Samariscus multiradiatus, is described from six specimens (four males and two females) collected in deep waters (296–430 m) around New Caledonia. The species is easily distinguished from its 16 congeners in having a combination of 85–91 dorsal fin rays, 67–72 anal fin rays, 5 pectoral fin rays, and 9 abdominal and 34–35 caudal vertebrae.

Contribution of amphidromous (Ooayu) and lake types (Koayu) of the landlocked Ayu (Plecoglossus altivelis altivelis) fish population in Lake Biwa to the next generation was investigated by isotopic approaches. δ15N values of eggs in adult ovaries distinctively differed between the two types. Contribution of Koayu, calculated using δ15N values of spawned Ayu eggs, was much greater than that of Ooayu in general, as previously reported. Ooayu spawned more eggs in the upper area of the spawning ground and did so late in the season. These results show the potential of isotopic approaches for identifying maternal life-history types of spawned eggs of migratory animals.

A new species of grouper, Epinephelus insularis is described based on 12 specimens (271.6–528.0 mm standard length: SL) from the western Pacific Ocean. The new species, previously confused with Epinephelus chlorostigma (Valenciennes in Cuvier and Valenciennes 1828), is distinguished from all congeners by the following combination of characters: dorsal-fin rays XI, 16 (rarely XI, 17); longitudinal scale series 114–132; total gill rakers 21–24; posterior margin of anal fin rounded; caudal fin truncate, its posterior margin with a narrow white line; head, body, and all fins with small polygonal brown spots (expanded on head and body undersurface) on a pale background, forming a reticulate pattern; and pectoral fin brownish. In addition, Serranus areolatus japonicus Temminck and Schlegel 1843, which has been regarded as a junior synonym of E. chlorostigma, is redescribed as a valid senior synonym of Serranus reevesii Richardson 1846 and Epinephelus tankahkeei Wu, Qu, Lin, Tang and Ding 2020. Epinephelus japonicus is characterized as follows: dorsal-fin rays XI, 17; longitudinal scale series 101–119; total gill rakers 23–26; posterior margin of anal fin rounded; caudal fin convex, without white lines; head, body (lateral surface only), dorsal, pelvic, anal, and caudal fins with small polygonal brown spots forming a pale reticulate pattern; and pectoral fin yellowish.

Pentanchus profundicolus is an enigmatic shark, characterized by a single dorsal fin. The holotype, which was collected in 1909 from the Philippines, had remained the only known example of the species for 90 years. A second specimen, collected from the same waters, is re-described. The presence of a single dorsal fin remains equivocal in so far as it represents the normal condition for the species. Aspects of the species' relationship with the species ofApristurus are discussed.

 During the R/V Hakuho-maru Cruise KH-95-2, Ocean Research Institute, University of Tokyo, from Tokyo, Japan to the South Pacific east of Australia (22° N–30° S; 126° E–176° E) from June to September, 1995, 77 unidentified gonostomatid larvae (5.5–20.0 mm SL) were collected south of 20° S with an IKMT net. They subsequently were identified as Sigmops longipinnis (Mukhacheva), and its ontogeny during the latter part of the larval stage (body form and proportions, photophores, pigmentation, and meristics) is described here. The larvae develop a species-specific row of melanophores along the midlateral line anterior to the caudal peduncle and another along the middorsal line from before the dorsal fin to just before the caudal fin.

Migration patterns of Japanese dace Pseudaspius hakonensis in and around Lake Biwa, Japan are unknown, although fluvial–lacustrine life history has been known in most tributaries, the many mature individuals migrating upstream into tributaries in early spring. Field surveys and stable isotope analyses were used to clarify the migratory history of Japanese dace in the Ishida River, inflowing to Lake Biwa. In the field surveys, the number of young of the year (YOY) individuals caught per unit effort (CPUE) by hand net and casting net in the tributary and lake-shore area was calculated. The CPUE peaked from May to July, after the spawning season, thereafter decreasing rapidly, suggesting that YOY Japanese dace migrated downstream to Lake Biwa immediately after emerging, possibly due to the abundant food resources there. From September to November, the CPUE of YOY individuals increased in the lower reaches of the stream, although their stable nitrogen isotope values were variable, in some cases being similar to those recorded in the upper reaches and the lake-shore area. This suggests that some YOY individuals migrate upstream from the lake in autumn. In the present study, the juvenile migration pattern of fluvial–lacustrine Japanese dace in Lake Biwa was described using a CPUE survey and δ15N and δ13C analyses.