Higher-level relationships of the basal teleosts are reviewed, with particular reference to the monophyly and interrelationships of the Elopomorpha.Since Greenwood et al. established in 1966 the Elopomorpha on the basis of eight putative synapomorphies, many authors have discussed validity of their monophyly through comparative observations of osteology, ontogeny, microstructure of spermatozoa, and physiology. Such circumstantial evidence have remained controversial, because none of them have reconstructed their phylogeny using character matrices derived from both morphological and molecular data. The same is true of long-standing controversy over phylogenetic positions of the Elopomorpha among major basal teleostean lineages, many authors simply demonstrating their “views” in the form of cladograms with putative synapomorphies until quite recently. Considering their morphological heterogeneity (from very primitive elopomorphs to highly derived eels) and ancient origins that presumably goes back to over a hundred million years ago, we concluded that corroboration of monophyly and determination of the phylogenetic position of the Elopomorpha should be based on comparisons of longer DNA sequences from many purposefully-chosen species. Recent development of a PCR-based approach for sequencing the fish mitochondrial genomes would be the most promising candidate for providing such data within a short period of time and they have actually resolved the latter problem in a recent study.
Freshwater-fish fauna of the Minami River system, Reinan Region, Fukui Prefecture, Japan, was investigated in 1998. Forty-five species in 14 families (including those newly recorded, such as Rhinogobius flumineus) were identified in the present research. Combined with data previously reported, a total of 55 species in 16 families, which included 36 primary and diadromous freshwater species (11 families), composed the fish fauna that could be considered naturally distributed in this river system. Compared to the richer fish fauna in western Japan regions, that of the Minami River system, representative of the Reinan Region, is poorer, and composed of peripheral fish fauna. The construction of many weirs and dams along the river system have prevented fish migration, causing more or less distinct fish assemblages to form in each of the upper, middle and lower reaches. Also, a number of species which inhabit small tributaries and/or irrigation channels in the Minami River System, such as Tanakia limbata, Acheilognatus tabira subsp.1 (sensu Hosoya, 1993), Lefua echigonia, Oryzias latipes, and the `nagare-hotokedojo'L. sp.(sensu Hosoya, 1993), have been threatened with extinction.
In 1993 and 1999, a number of specimens of a poecilid fish collected from a drainage area of the hot spring at Kojyohama, Shiraoi-cho, Shiraoi-gun, southern Hokkaido, Japan was identified as Poecilia sphenops. Identifications were based on males having elongated pelvic-fin tips, in having the dorsal-fin origin posterior to a vertical through the pelvic-fin base, 9-10 dorsal fin rays, no horizontal pigment band and ocellus on the body, no opening of the cephalic sensory canal on the snout, and many tricuspid teeth in the inner row of teeth on the upper jaw. It is believed that small fish were introduced into this area longer than 20 years ago to assist in reducing mosquito populations. At present, high density schools of these small fish were observed swimming throughout the drainages. This report represents the record of habitation and natural breeding of this species in Japan.
Larvae and a juvenile of two tetragonurids, Tetragonurus cuvieri (8 specimens, 6.8-18.5 mm BL) and T.atlanticus (4 specimens, 6.0-10.9 mm BL), collected by larval net from waters off eastern Japan, represent the first records of such from the North-West Pacific. Both species possessed spines on the interopercle and subopercle in their early life stages, a juvenile (18.5 mm BL) of T.cuvieri having one spine on each element, and a postflexion larva (10.8 mm BL) of T.atlanticus having two interopercle spines and one subopercle spine.
To examine the birth seasons of Japanese embiotocid fishes, Ditrema temmincki, D. viridis and Neoditrema ransonneti, samples were collected at Otsuchi Bay northern Japan in July 2000. Specimens of the three species were divided into small and large size groups, respectively. Large groups included gravid females and females just after parturition. Most embryos extracted from the gravid females were grown and ready to birth. All fish of the small groups were slightly larger than the embryos, indicating that the former fish were young just after birth. Thus, the birth seasons of the three species appeared to be from July to early August. Their annual reproductive cycles may differ from those in southern Japan where the birth seasons have been reported being from May to July.