Two voucher specimens of the spined loach, Cobitis matsubarae Okada and Ikeda, 1939, collected from the Shonai River, a branch river of the Oyodo River system, southern Kyushu, Japan, represent the first reliable record of that species from the Oyodo River system. Morphological features of the male lamina circularis, prepelvic myotome number, maxillary barbel length, snout length, body pigmentation patterns, and genetic characteristics of mtDNA cytb sequences were in close agreement with characters those of C. matsubarae. Together with C. sakahoko, C. matsubarae, is considered to be distributed naturally in the Oyodo River system.
Inter- and intraspecific variations in 2-dimensional otolith morphology were investigated in three sympatric species of Ammodytes (Perciformes: Ammodytidae) from Japan, viz., A. japonicus Duncker and Mohr, 1939, A. hexapterus Pallas, 1814 and A. heian Orr, Wildes and Kai, 2015. Size-dependent measurements and elliptic Fourier analyses of otolith outlines failed to show significant differences among the three species. However, both investigating methods revealed intraspecific variations relative to body length in each species, indicating ontogenetic changes in otolith morphology. The occurrence of several outlier specimens suggested a variable pattern of ontogenetic changes among individuals and/or between developmental stages.
The mottled skate Beringraja pulchra, distributed in the western North Pacific, is a commercially important species, directly targeted by Japanese and Korean fisheries. Despite a recently decreasing catch rate, no studies of population structure, crucial to sustainable fisheries management and conservation practices, are known to have been made. Because skates generally have low dispersal ability and are likely to have an extensive population structure, due to large benthic egg capsules and no pelagic larval stage, the population structure of the species was assessed on the basis of sequence variations of the mitochondrial DNA cytochrome c oxidase subunit I (COI) 592 bp (in 166 individuals) and morphological variations in seven morphometric characters (in 192 individuals), representing five areas, including Hokkaido, Japan [coasts along Sea of Okhotsk, Pacific Ocean, and Sea of Japan (the East Sea of Korea)], western Sea of Japan, and Yellow Sea. The genetic analysis detected 12 haplotypes, six being shared among the sampling areas, although significant pairwise ΦST estimates indicated restricted gene flow among the sampling areas (excluding those off the Hokkaido). The extensive population structure of the species was also supported by morphological differences in several characters, such as disc length, disc width, and eye diameter. Beringraja pulchra was concluded as being clearly structured into three populations for future management, viz. Hokkaido, western Sea of Japan, and Yellow Sea populations. This population structure may have been shaped by the Tsushima Current flowing between the Korean Peninsula and the Japanese Archipelago, the species generally inhabiting colder water.
Difficulties in distinguishing between morphologically similar species, such as Phoxinus lagowskii steindachneri and Phoxinus oxycephalus jouyi, whose distributions overlap in the Kinki region, are significant for assessments of biodiversity and conservation, in addition to taxonomic status. Morphological analyses were undertaken on Phoxinus specimens (n = 75) collected in the Ishi and Chihaya rivers (Yamato River basin, Osaka Prefecture), and compared with type specimens (syntypes of Phoxinus steindachneri, Sauvage, 1883 and paratypes of Leusiscus jouyi, Jordan and Snyder, 1991) and non-type museum specimens (Phoxinus oxycephalus jouyi). Mitochondrial DNA (mtDNA) analyses of 16 individuals were also undertaken. Two distinct types of Phoxinus were recognized, differing morphologically in the presence or absence of a black horizontal band on the side of the body and scale numbers above the lateral line, and separated by a principal component analysis of 9 characters. In addition, 12 haplotypes (identified in the present and previous studies) were variously associated within two genetically different groups, corresponding to two ecological types that inhabit the upper and middle parts of the Yamato River, respectively. Because reproductive isolation is already clearly established between the two types, their recognition as separate species (Phoxinus lagowskii steindachneri and P. oxycephalus jouyi) in the Ishi and Chihaya rivers is upheld.
Topmouth gudgeon (Pseudorasbora parva; Japanese name, motsugo), originally distributed in western Honshu, Shikoku and Kyushu, has been artificially introduced well north of its natural distribution area, to the Tohoku region and Hokkaido. The occurrence of topmouth gudgeon in the pond of Notsukeushi park at Kitami City, Hokkaido, the first record of the species in the Okhotsk region, was established and the population size estimated using the mark-recapture method. Although more than 2,000 fish between 1 and 4 years old were determined as living in the pond, none were found in either the inflow and outflow rivers, despite their apparent suitability. Further efforts in public educations are required to prevent further spreading of this fish.
The Itasenpara bitterling Acheilognathus longipinnis is a small cyprinid fish belonging to the Acheilognathinae, a subfamily that has an unusual symbiotic spawning relationship with freshwater mussels. During the spawning period, mature males select a mussel to accommodate spawning of a female. Because females possess short ovipositors for inserting their eggs inside the suprabranchial cavity of the host mussel via the exhalant siphon, the pattern of mussel utilization by spawning Itasenpara bitterling was investigated in the Moo River and a conservation pond (Himi City, Toyama Prefecture, Japan), so as to clarify the most preferred mussel size. In the Moo River (lotic environment), Nodularia douglasiae nipponensis (38.8% of total 747 individuals) was the major host of A. longipinnis larvae, there being no obvious size preference, possibly because neither eggs nor larvae of A. longipinnis could be readily ejected from the host in the lotic environment. By contrast, in the conservation pond (lentic environment), where N. d. nipponensis (24.3% of total 136 individuals) was again the main host of A. longipinnis larvae, a tendency to prefer smaller-sized mussels was apparent, due to the ease of ejection of eggs and larvae of A. longipinnis from larger-sized hosts (shell length >66 mm) in the lentic environment. Accordingly, differences in host mussel suitability are suggested as being related to habitat differences.
To clarify the ichthyofauna of the Amami Island Ryukyu Archipelago, fish specimens from the region were examined in museums throughout Japan resulting in the discovery of a single specimen (75.9 mm standard length; SL) of the dwarf squirrelifish Sargocentron iota Randall, 1998 (Beryciformes, Holocentridae) in the Yokosuka City Museum. Collected from a deep (23m) dark recess in a rocky reef grotto at a rocky reef off Kakeroma Island. The specimen was characterized by XI, 13 dorsal-fin rays, IV, 9 anal-fin rays, 15 pectoral-fin rays, I, 7 pelvic-fin rays, 6 + 10 + 9 + 5 caudal-fin rays, 45 lateral-line scales, 3.5 scale rows between the mid base of the spinous dorsal fin and the lateral line, 9 scale rows between the lateral line and anal-fin origin, 4 oblique scale rows on the cheek, 5 + 10 gill rakers, 11 + 16 vertebrae, body depth 2.5 in SL, head length 2.7 in SL, head depth 3.6 in body depth, snout length less than half orbital diameter, upper-jaw length 2.6 in head length, fourth dorsal-spine longest, third dorsal-fin soft ray longest, a pair of retrorse spines on the edge of the premaxillary groove, a spine on the upper edge of the lacrimal absent, and a bright red body coloration when fresh. The longest anal-fin soft ray length of the Kakeroma Island specimen was slightly shorter than that of the type specimens of S. iota which is likely to be an individual or geographic variation. Although S. iota is distributed in the Indo-Pacific, it has been recorded only from the Hawaiian Islands and Palau within the North Pacific Ocean. Accordingly, the Kakeroma Island specimen represents the first record of S. iota from Japanese waters and the northernmost record for the species. The new standard Japanese name “Kogashira-ebisu” is proposed for the species.