Hitoshi Ida

A ‘living fossil’ eel (Anguilliformes: Protanguillidae, fam. nov.) from an undersea cave in Palau

We report the discovery of an enigmatic, small eel-like fish from a 35 m-deep fringing-reef cave in the western Pacific Ocean Republic of Palau that exhibits an unusual suite of morphological characters. Many of these uniquely characterize the Recent members of the 19 families comprising the elopomorph order Anguilliformes, the true eels. Others are found among anguilliforms only in the Cretaceous fossils, and still others are primitive with respect to both Recent and fossil eels. Thus, morphological evidence explicitly places it as the most basal lineage (i.e. the sister group of extant anguilliforms). Phylogenetic analysis and divergence time estimation based on whole mitogenome sequences from various actinopterygians, including representatives of all eel families, demonstrate that this fish represents one of the most basal, independent lineages of the true eels, with a long evolutionary history comparable to that of the entire Anguilliformes (approx. 200 Myr). Such a long, independent evolutionary history dating back to the early Mesozoic and a retention of primitive morphological features (e.g. the presence of a premaxilla, metapterygoid, free symplectic, gill rakers, pseudobranch and distinct caudal fin rays) warrant recognition of this species as a ‘living fossil’ of the true eels, herein described as Protanguilla palau genus et species nov. in the new family Protanguillidae.

Species composition and dynamics of larval and juvenile fishes in the surf zone of Mauritius

The importance of the surf zone as a nursery ground for larval and juvenile fishes has been widely recognized, however the zone has yet to be studied in Mauritius. Recently, the coastal area of the island has been increasingly affected by human activities, especially by tourism. We collected fish samples with a hand pulled seine net during the period of August 2001 to March 2003 to clarify the fish fauna and the dynamics of fishes in the surf zone. Two sampling sites adjacent to river mouth areas and one sampling site adjacent to a mangrove area were selected for comparison of fish fauna in relation to environmental conditions. A total of 9,429 fish larvae and juveniles, representing at least 112 species from 48 families were collected. The abundant species were hardyhead silverside, Atherinomoruslacunosus, bluespot mullet, Valamugil seheli, and Ambassis spp., each contributing 16.2, 12.4, and 11.8% of the total number of individuals, respectively. Estuarine species dominated in the surf zone adjacent to the river mouth areas. Species composition and diversity changed seasonally. The number of fish increased during the rainy season. Species diversity increased at the turn of the seasons from the dry season to the rainy season. We conclude that species composition in each site was affected by environmental factors, such as the scale of the flux from the rivers, which is related to the precipitation. The results indicated that freshwater from the river is a trigger to aggregate larvae and juveniles in the surf zone.

Effects of thyroid hormones on phototaxis of chum and coho salmon juveniles

Abstract Changes in phototaxis of chum ( Oncorhynchus keta ) and coho ( O. kisutch ) salmon were examined after treatment with thyroid hormones, using troughs (0.25 × 2 m long, 20 cm deep) with open (1200–2400 lux, 1 m long) and shaded (400–680 lux, 1 m long) water. In some experiments, half of the trough was covered to provide shelter ( 4 , 30 mg 150 l , immersion) or thiourea ( 15 g 150 l , immersion) for 56 days from early April. Coho smolts were treated with triiodothyronine (T 3 , 15 mg 150 l , immersion) for 4 days in July–August. T 4 -treated chum preferred open water by 80–90%. More than 78% of fry treated with thiourea and the control preferred to be in shade or to be in shelter. T 3 -treated coho preferred open water after 3 and 4 days, whereas the control fish stayed in shaded water. The preference of T 3 -treated fish for open water was observed 1 week after the end of treatment and the preference disappeared during the following week. These findings suggest that thyroid hormones play an important role in the phototaxis of salmonids in freshwater.

Epigonus cavaticus (Teleostei: Perciformes), a new epigonid fish from Palau, western Central Pacific

A new epigonid fish, Epigonus cavaticus, is described on the basis of eight specimens (59.2–69.5 in standard length: SL) collected from a cave at depth 20 m, southern fringing reef of Ngemelis Island, Palau. The species differs from other congeners by having minute teeth on both jaws, no opercular spine, pyloric caeca 7–8, gill rakers 25–27, total pored lateral line scales 48–50, dorsal fin rays VII-I, 10–11 (mode VII-I, 10), pectoral fin rays 16, vertebrae 10 + 15, body depth 21.4–25.0% SL, pectoral fin length 22.7–24.6% SL, eye diameter 44.4–47.5% head length: HL, upper jaw length 40.2–42.5% HL. Four paratypes (63.7–66.8 mm SL) of the new species are female with mature gonads, it is the smallest in size at sexual maturity among the congeners.

Acropoma argentistigma, a new species from the Andaman Sea, off southern Thailand(Perciformes: Acropomatidae)

Abstract A new acropomatid fish, Acropomaargentistigma, is described on the basis of six specimens (59.0–107.5 mm in standard length) from the Andaman Sea, off southern Thailand (Phuket Island). The new species is distinguished from all other congeners by the combination of the following characters: a short U-shaped luminous gland, 16–18 gill rakers, anus situated about midway along depressed pelvic fin, proximal radial of first anal fin pterygiophore with a trough, a single row of well-developed conical teeth on the lower jaw, and head length 40.0–41.1% of standard length.

Stock structure of Japanese flounder inferred from morphological and genetic analyses

Stock structure of Japanese flounder Paralichthys olivaceus has been inferred mainly from either morphological or genetic analyses. However, because the results of both analyses did not always agree with each other, an inclusive conclusion has never been obtained. In this study, the stock structure has been inferred from both morphological and genetic analyses using 722 wild Japanese flounder collected from nine locations along the Japanese coast. The dorsal and anal fin ray counts were larger in the southern than in the northern populations. In total, 1041 bp of mitochondrial NADH dehydrogenase subunit-2 (ND2) and 1830 bp of ND5 sequences were aligned. There are 578 variable sites in the concatenated sequence from the two genes, which defined a total of 490 haplotypes. Both results of morphological and genetic analyses indicated that the western Kyushu group, which included the Nagasaki and Kagoshima populations, was divided from the other seven populations. This is the first report to reveal the heterogeneity of the western Kyushu group based on statistical analysis.

Development and distribution of the early life stages of the longfin pearleye Benthalbella linguidens (Aulopiformes: Scopelarchidae) in the western North Pacific

The early life history and development of the scopelarchid Benthalbella linguidens was studied, based on 203 specimens (from 5.3 to 89.7 mm in body length: BL) collected from Kuroshio, Oyashio waters and transition waters of the western North Pacific. The early life stages of B. linguidens are distinguished from those of other species of Benthalbella that inhabit the North Pacific by the characters of 62–64 myomeres in the larval stage and 26–28 anal fin rays in juvenile and transforming specimen. Larvae are elongate; notochord flexion begins at ca. 12 mm BL and is completed at ca. 15 mm BL. The fin ray complements are established at ca. 40 mm BL. The single transforming specimen (89.7 mm BL) that has peritoneal pigment was collected from transition waters. All larvae were collected from Kuroshio and transition waters from winter to early summer; however, the size of larvae in Kuroshio waters was apparently smaller than that in transition waters, with ranges of 5.3–32.4 mm BL (mean 17.1) and 15.3–35.3 mm BL (mean 27.5), respectively. Juveniles were distributed in transition and Oyashio waters and were absent in Kuroshio waters, where adults are commonly distributed. These occurrences of larvae and juveniles in the western North Pacific indicate that B. linguidens spawns in Kuroshio waters in winter and uses transition waters as nursery grounds.

Description of a postflexion larva specimen of Liopropoma japonicum from off Izu Peninsula, Japan

Three tribes of serranids, Liopropomini, Diploprionini, and Grammistini, are defined by Baldwin and Johnson (1993) as a monophyletic group of the subfamily Epinephelinae. The most salient feature of the monophyletic group is the presence of elongate, filamentous dorsal-fin spine(s) in larvae (Baldwin and Johnson, 1993). In the group, the elaborate elongate dorsal-fin spines in larvae of the genus Liopropoma (tribe Liopropomini) are well known by many cases; however, little progress has been made in identifying larval specimens of Liopropoma to species (Kotthaus, 1970; Fourmanoir, 1976; Kendall, 1979, 1984; Baldwin et al., 1991; Limouzy-Paris et al., 1994). In this article, we describe the morphological characters of a postflexion larva specimen of Liopropoma japonicum.

Karyotypes and cellular DNA contents of three species of the subfamily Clupeinae

Karyotypes of three species of the subfamily Clupeinae collected from northern Japan were analyzed by in vitro methods and their cellular DNA contents were measured using an integrating microdensitometer.Sardinella zunasi andSardinops melanostictus show very similar karyotypes: 2n = 48, consisting of acrocentric or subtelocentric chromosomes with a gradual decrease in chromosome size, but with differences in cellular DNA of 2.32 and 2.69pg/cell respectively.Clupea pallasii differs from the aforementioned species in karyotype: 2n = 52, consisting of 6 metacentric or submetacentric chromosomes and 46 acrocentric or subtelocentric chromosomes, with a cellular DNA content of 1.96 pg/cell. The results showed two different modes in karyological evolution within the subfamily Clupeinae, i.e. an increase of cellular DNA content without apparent change in karyotype, as shown bySardinella zunasi andSardinops melanostictus, and less change in cellular DNA content but with marked change in karyotype, as shown byClupea pallasii.

Larval and juvenile development of the medusafish, Icichthys lockingtoni (Perciformes: Centrolophidae), from the Northwest Pacific, and a comparison with Northeast Pacific larval and juvenile forms

Abstract Larval and juvenile development of Icichthys lockingtoni are described and illustrated based on specimens collected off northeastern Japan. Some osteological characters are detailed, and comparisons are made with previous descriptions from the Northeast Pacific. Postflexion larvae (11.7–15.4 mm BL) had small preopercular spines; juveniles (19.5–42.2 mm BL) had weakly serrated outer margins of the preopercle, interopercle, and subopercle. In late juveniles (about 40 mm BL), the second and third epurals fused, the epurals thereafter comprising two elements.