The fish collection built up by Chiyomatsu Ishikawa (1860–1935), a Japanese zoologist who investigated the fish fauna of Lake Biwa in the 1890s, was reassessed for the first time in many years, and found to provide an important insight into the fish fauna of the lake at the end of the 1800’s. Now held in the National Museum of Nature and Science, Tsukuba, Japan, the collection includes 1,795 specimens (110 lots) collected from 12 sites in Lake Biwa and adjacent areas (i.e., Hikone, Imazu, Kaizu, Kaminyu, Lake Yogo, Maebara (= Maibara), Matsubara, Nagahama, Omi-Hachiman, Seta River, Shiotsu and Zeze). Thirty-three species, including 10 endemic species/subspecies, in 11 families were identified, including the type series of Pseudogobio zezera (=Biwia zezera). The majority of specimens were included in the following 7 species: Tanakia lanceolata, Acheilognathus tabira tabira, Candidia sieboldii, Ischikauia steenackeri, Sarcocheilichthys variegatus microoculus, Tachysurus nudiceps, and Plecoglossus altivelis altivelis (landlocked type). Such species are now seen infrequently along the lake foreshore (except for P. a. altivelis), the collection indicating a formerly rich fish fauna before the establishment of artificial influences (e.g., concrete revetments, invasion of alien species such as Micropterus nigricans and Lepomis macrochirus, and artificial control of water levels by the Seta River Weir). Although the occurrence of Acheilognathus longipinnis and Sarcocheilichthys variegatus variegatus in Lake Biwa has been unclear for a long time, examples of those species/subspecies in the collection provided evidence of their past distributions in the lake. Importantly, the collection sets a benchmark for any restoration of the past fish fauna of Lake Biwa.
The ceratoid anglerfish genus Dolopichthys Garman, 1899, distributed in the bathypelagic zone of all three major oceans, is characterized by the following combination of characters: females with well-developed sphenotic spines; body relatively long and slender, not globular; pectoral-fin lobe short, shorter than the longest pectoral-fin rays; skin naked and entirely smooth; lower jaw with a well-developed symphysial spine; pterygiophore emerging on the snout from between the frontal bones; caudal peduncle depth less than 20% of standard length (SL); quadrate spine well developed; frontal bones long and straight; hyomandibula with a double head. The genus includes seven valid species, Dolopichthys allector Garman, 1899, Dolopichthys danae Regan, 1926, Dolopichthys longicornis Parr, 1927, Dolopichthys jubatus Regan and Trewavas, 1932, Dolopichthys pullatus Regan and Trewavas, 1932, Dolopichthys dinema Pietsch, 1972, and Dolopichthys karsteni Leipertz and Pietsch, 1987, with only D. longicornis being known from Japanese waters to date. A single female specimen (88.6 mm SL) of the rare species D. danae, was collected at a bottom depth of 902–917 m off Iwate Pref., Pacific coast of northern Japan, on 12 October 2022. The specimen was distinguished from other congeners by a longer illicium (length 70% SL), dorsal midline of the escal bulb with two darkly pigmented, distally bifurcating papillae, vomer without teeth, and lower jaw with ca. 150 teeth. Dolopichthys danae was previously known from six specimens only, all from the North Atlantic (south of 40˚N), the present specimen therefore representing the seventhknown specimen and first record of the species from the Indo-Pacific, including Japanese waters. The new standard Japanese name “Enaga-mimizuku-rakuda-anko” is proposed for the species.
Two species of lefteye flounder (Bothidae), Engyprosopon mozambiquense Hensley, 2003 and Engyprosopon parvipectorale Amaoka and Ho, 2018, are newly recorded from Japan based on five specimens (one male and four females) and a single male specimen, respectively, from Nakagusuku Bay, Okinawa Island, Ryukyu Islands. The two species resemble each other in sharing the following combination of characters: extremely narrow interorbital space; large mouth (posterior margin of ocular side upper jaw extending beyond anterior margin of lower eye); inner margin of gill rakers with serrae; and a pair of dark blotches on caudal fin absent. However, the present male specimen of E. mozambiquense differed from male specimens of E. parvipectorale from Taiwan and Japan in having a greater interorbital width, 11.5 in head length (vs. 23.1–67.7 in male E. parvipectorale), a rostral spine on the ocular side of the snout (vs. absent), and three dark blotches on the ventral surface of the ocular side lower jaw (vs. uniformly black). The present female specimens of E. mozambiquense were characterized by having small teeth on both jaws (vs. anterior teeth on the upper jaw, and all teeth on the lower jaw large and canine-like in both male and female E. parvipectorale). The two species are also similar to the Japanese endemic congener, Engyprosopon kushimotoense Amaoka, Kaga and Misaki, 2008 (known only from the male holotype from Wakayama Prefecture), and Engyprosopon longipelvis Amaoka, 1969 (known from southern Japan) in having gill rakers with serrae and a narrow interorbital space. However, E. kushimotoense and E. longipelvis differ from the former in having 43 and 37–42 lateral-line scales, respectively (vs. 49–52 in E. parvipectorale and 46–52 in E. mozambiquense). The new standard Japanese names “Yorime-darumagarei” and “Kiba-yorime-darumagarei” are proposed here for E. mozambiquense and E. parvipectorale, respectively.
Five specimens of scaleless dragonfish of the genus Melanostomias (Stomiidae: Melanostomiinae) were collected off the Ogasawara Islands, southern Japan and Fukushima Prefecture, Pacific coast of northern Japan. The specimens conformed to Melanostomias nigroaxialis Parin and Pokhilskaya, 1978 as follows: tips of the upper and lower jaw teeth bifurcated; chin barbel distally expanded from midpoint, the dorsal and ventral expanded areas membranous and transparent, and including small luminous bodies; a single ovoid body without a terminal filament on terminal part of chin barbel; distinct luminous patch on dorsal surface of head absent; and axis of chin barbel almost entirely black, except terminal part. However, the present specimens had a shorter chin barbel than noted in the original description of M. nigroaxialis. Because a plot of barbel lengths (as % of standard length) versus standard length of the present specimens and three specimens examined in the original description indicated that barbel lengths tended to decrease with growth, the difference in barbel length between the two groups of specimens was consistent with intraspecific variation. In addition, the present specimens had different numbers of VAV, AC, IC, VAL and OA photophores compared with the original description of M. nigroaxialis, although the ranges were less than the those in many congeneric species, also indicative of intraspecific variation. Consequently, the present specimens were identified as M. nigroaxialis, previously known only from the Banda Sea, southern Philippines Sea and northern New Zealand. This is the northernmost record of M. nigroaxialis, and first from Japanese waters. The new standard Japanese name “Tomoshibi-kanten-tokagegisu” is proposed for this species.
A single specimen (440 mm in total length) of the genus Ophichthus Ahl, 1789 (Anguilliformes: Ophichthidae), captured during a bottom trawl survey at a depth of 351– 353 m off Ibaraki Prefecture, Pacific coast of northern Japan, was identified as Ophichthus longicorpus Vo and Ho, 2021, due to the following combination of characters: 29 predorsal and 162 total vertebrae; head length 8.4% of total length; dorsal fin origin situated at 5.0 pectoral fin length (1.2 head length) behind head; pre-dorsal length 19.5% of total length; pectoral fin length 25.6% of head length; pectoral-fin tip slightly pointed; and body without spots and bands. The present specimen represents the second record of the species since its original description, based on Vietnamese specimens, and adds considerable northern and eastern extensions to its known distribution. On the other hand, a number of morphological differences were apparent between the Japanese (n = 1) and Vietnamese (n = 13) specimens, including differences in cephalic sensory pore numbers (1 + 3 = 4 in the supraorbital series and 5 in the mandibular series in the former vs. 1 + 4 = 5 and 6 in the latter), and anus position (somewhat anterior to the middle between the snout tip and tail tip vs. almost in middle). The differences are presently considered to represent intraspecific variations, due to the wide range of morphological variations recorded in other species of Ophichthus, although further taxonomic considerations may be in order pending the availability of a greater number of widely-distributed specimens. The new standard Japanese name “Azuki-umihebi” is proposed for the species, referring to its reddish-brown body coloration.
The pipehorse genus Solegnathus Swaison, 1839 is divided into two subgenera, Solegnathus Swaison, 1839 (superior trunk ridge discontinuous, with superior tail ridge) and Runcinatus Whitley, 1929 (ridges continuous), the former including Solegnathus (Solegnathus) hardwickii (Gray, 1830), S. (S.) lettiensis Bleeker, 1860, S. (S.) spinosissimus (Günther, 1870), and S. (S.) robustus McCulloch, 1911, and the latter, S. (Runcinatus) dunckeri Whitley, 1927. Of these five species, only S. (S.) hardwickii and S. (S.) lettiensis, have been recorded to date from Japanese waters, the latter being known from only two specimens [259.6 mm and 284.6 mm total length (TL)], both reported from the middle of the Okinawa Trough, southern East China Sea in 1978. However, a single specimen (KAUM–I. 182558, 367.0 mm TL) of S. (S.) lettiensis was found on a beach on Kamikoshiki-shima Island, Koshiki Islands, northern East China Sea, Kagoshima Prefecture, Japan in December 2022, probably a discarded bycatch from a deepwater bottom trawl fishery operating off the island. The specimen was characterized by having the superior trunk ridge discontinuous, with a superior tail ridge; opercular membrane without bony side platelets; body surface mainly tuberculate; length of dorsal-fin base 1.41 in head length; 23 trunk rings; and 74 total rings, and its identification confirmed after comparison with the two previously-collected specimens (above). The former, representing the second Japanese record and northernmost record of S. (S.) lettiensis, is described herein in detail, and the new standard Japanese name “Shinkai-sumitsuki-yoji” proposed for the species.
Two egg population samples, G2901 (n = 27) and G2902 (n = 22), were collected from a shingle beach along the northern coast of the North Basin of Lake Biwa, Japan. Eight eggs were randomly selected from each sample and the mitochondrial 12S rRNA region was partially sequenced (177 bp). All 16 eggs shared a single haplotype and were identified as Pseudogobio esocinus based on phylogenetic analysis. To date, eggs of this species found in lake environments (including those of the lakes other than Lake Biwa) have been reported only from a single sandy gravel beach along the eastern coast of the North Basin of Lake Biwa. The present finding is the first record of P. esocinus eggs from a shingle beach.
Fifteen specimens of the Chinese false gudgeon Abbottina rivularis were collected from three rivers in the Lake Biwa–Yodo River system, Kyoto Prefecture, Japan for the first time in 38 years. A molecular phylogenetic analysis of mitochondrial cytochrome b gene sequences indicated that the specimen haplotypes completely matched two haplotypes included in the Honshu clade of the Japanese lineage, suggested as indigenous to Japan in a previous study. Further surveys are necessary to reveal the origin and distribution of the species in Kyoto Prefecture, and future conservation requirements, in addition to progressing biogeographic studies in the Kinki region.
A fish specimen [ca. 39 cm standard length (SL)] collected on 11 November 2022 in the Azuma River (a small urban river feeding the South Basin of Lake Biwa) was identified as Biwa salmon (Oncorhynchus masou subsp.), based on morphology and DNA analysis of the mitochondrial ATPase6 and CO III genes. Although the specimen when collected was in very poor condition, lacking several vertebrae and internal organs (including the gonads), the jaw shape, nuptial color on the body, and white abraded caudal peduncle surface indicated that it was a mature female that had attempted to dig a spawning bed. The river-run specimen represents the first specimen-based record of the subspecies in a river flowing into the South Basin of Lake Biwa, and the southernmost river-run record.
Sneaking behavior directed towards a pair of Lake-run form Biwa salmon (ca. 50 cm TL) by a mature male parr (ca. 10cm TL), observed in the Oura River, a small inlet stream of Lake Biwa, central Japan on 25 October 2020, resulted in successful sperm release by the latter. If the parr individual was a Biwa salmon, the observation is important for improved understanding of spawning in the latter, as such sneaking has not been previously recorded with any certainty. On the other hand, if the parr was a stocked Amago salmon individual, it likely represented an unregulated stock, the release of such possibly promoting genetic introgression into the Lake-run form. A third possibility, that the sneaking parr was a native Amago salmon, would support the hypothesis that outbreeding occurs between native Amago salmon and Biwa salmon in the Lake Biwa water system.
Four collected gobiid specimens (55.3–87.6 mm in standard length) and a single photographed and released individual, from the coast of Miyazaki Prefecture, Kyushu, southern Japan, were identified as the endemic Japanese species Siphonogobius nue Shibukawa and Iwata, 1998, characterized by a simple infraorbital canal extending below the eye, and the oculoscapular canal between pore’s A' and L' lacking other pores, except for pore D. The species has been recorded to date from the Pacific coast of Honshu, northeastern Japan (between Fukushima and Shizuoka prefectures), the present specimens representing the southernmost known record of the species. A detailed description and color photograph of the Kyushu specimens is provided.
A single specimen (95.0 mm standard length) of Tomiyamichthys russus (Cantor, 1849), an Indo-Pacific goby associated with alpheid shrimps, was collected from Tanegashima Island, Osumi Islands, Satsunan Islands, Kagoshima Prefecture, Japan. In Japanese waters, the species has previously been recorded only from the Okinawa-jima and Iriomotejima islands (central and southern Ryukyu Islands). Thus, the Tanega-shima specimen, described in detail herein, represents the first record of T. russus from the Satsunan Islands (third Japanese record), and northernmost record for the species.
Nagaremon-charr, a rare morphotype of Salvelinus leucomaenis characterized by wavy parr markings (Nagaremon type) instead of typical parr marks (normal type), inhabit a tributary of the Ane River basin (Lake Biwa system). However, the frequency of the Nagaremon type has decreased from the 1970s. To explain this reduction, mating trials were conducted between the Nagaremon and normal morphotypes. One trial yielded populations that approximated a 1:1 segregation ratio for the two phenotypes, suggesting that the Nagaremon type is a recessive trait and that the parent with a normal phenotype (collected from the tributary) was a heterozygous carrier for the Nagaremon trait. Therefore, conservation of Nagaremon-charr should involve management of the entire tributary, thereby including normal type charr.