Lake Biwa Museum

Kusatsu, Japan

Lake Biwa Museum

Kusatsu, Japan

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Fujioka Y.,Lake Biwa Museum | Ueno S.,Shiga Prefecture Fisheries Experiment Station
Fisheries Science | Year: 2014

The honmoroko has been inferred to have an XX/XY sex determination system, but the parental genome can also affect the sex ratio of the offspring. The extent of parental effects on sex determination was examined by checking the sex ratios of F1 and F2 gynogenetic diploids and control diploids. Eleven gynogenetic broods from different females consisted of all or nearly all females, but eight broods showed a variable proportion of males (<50 %). One second-generation brood of gynogenetic diploids consisted wholly of females, but others produced some males. In crosses with a control diploid female, four males from a high-percentage male brood of gynogenetic diploids produced offspring with a balanced sex ratio. Sib-mating between a gynogenetic female and three gynogenetic males from the brood produced predominantly male progeny. These results suggest that there are at least four possible genotypes: genotypic female (XX), phenotypic female carrying a silent Y chromosome, genotypic male (XY), and genotypic supermale (YY). These inferences suggest that this fish has an XY system but a relatively high proportion of females possess a mutated, silent Y chromosome which does not lead to testis formation. © 2014, Japanese Society of Fisheries Science.


Morphology of trunk limbs of the laevicaudatan branchiopod Lynceus biformis (Ishikawa, 1895) varies along the anterior/posterior axis of the body. On anterior limbs, the praecoxal endite is elongate and strongly flexed, endites of the coxa and basis are broad, and lobes of the endopod are elongate. On more posterior limbs protopodal endites and endopodal lobes are more similar to each other and none is particularly long or broad. In addition, an exite fails to form on more posterior limbs, and the exopod becomes progressively reduced in males or modified in females. Sexual dimorphism is expressed by fewer trunk limbs, 10, and a transformed trunk limb 1 of males, as well as by a modified exopod of posterior trunk limbs 8-12 of females. Development of all limbs includes an asetose step and several setose steps; some limb pairs may begin as a transverse bilobate flap. Developmental changes include the progressive addition of limbs posteriorly, addition of endites and lobes to some limbs, addition of an exite and proximal rod-like structure during the transformation to a setose limb, and the transformation of sexually dimorphic limbs during the molt to the adult. Naupliar asetose limbs 1-5 have fewer endites and lobes than the more posterior asetose limbs of juveniles have. The male clasper of L. biformis is a subchela formed from the basis and the distal segment of the endopod; the proximal and middle endopodal segments are closely associated with the subchela. In contrast, the clasper of male spinicaudatans is a subchela formed from the distal endopodal segment and the proximal of two middle segments of the endopod. The distal of the two middle endopodal segments and the palp it bears (together, the so-called "articulated palp") are absent in the clasper of L. biformis. The modified exopod on trunk limbs 7-10 of females of L. biformis has no similarly transformed counterpart on limbs of female spinicaudatans. There is no discoid endite on the trunk limb of L. biformis as there is on trunk limbs of spinicaudatans, and no setose attenuate endite either, although the asetose rod-like structure may be homologous to the latter. © Koninklijke Brill NV, Leiden, The Netherlands 2012.


Previous studies from southern Japan reported larval stages of eight gnathiid isopod species parasitising coastal elasmobranchs. Since gnathiid larvae of these different species closely resembled each other, it was necessary to obtain specimens of free-living adult males for identification to the species level. This was achieved by allowing larvae of the final stage to moult into adult males. From these males, specimens of a species new to science were discovered and described here as Gnathia rufescens n. sp. The main differentiating characteristics of G. rufescens n. sp. are: (i) the apex of pleotelson is oval shaped; (ii) the dorsal sulcus is wide in the posterior part; and (iii) the article 3 of the pylopod is not reduced in the male. Additionally, this paper summarises the specific pigmentation patterns of third-stage larvae of the new species and eight previously described species. Furthermore, host records and host use by the gnathiids were summarised based on data from 158 hosts and over 4,500 gnathiid samples; these are discussed with a focus on host-specificity of the nine gnathiid species studied. © 2015, Springer Science+Business Media Dordrecht.


During surveys of a variety of groundwater, spring and interstitial habitats (e.g. in river bars, domestic wells, springs, and seeps) in Shiga Prefecture, Japan, a total of 15 ostracod species were recovered and identified. Three species and one genus are described for the first time herein, Undulacandona spinula n. gen & n. sp., Cryptocandona tsukagoshii n. sp. and Cavernocypris cavernosa n. sp.. Microdarwinula zimmeri (Menzel, 1916) is reported for the first time from Japan. Dolerocypris ikeyai Smith & Kamiya, 2006, Eucypris pigra (Fischer, 1851) and Cryptocandona brehmi (Klie, 1934) are new records for Shiga Prefecture. © 2011 · Magnolia Press.


Kawase S.,Kinki University | Hosoya K.,Lake Biwa Museum
Ichthyological Exploration of Freshwaters | Year: 2015

Pseudorasbora pugnax, new species, is described from the Ise Bay area in central Honshu, Japan. It is distinguished from its Japanese congener P. pumila by the absence of a dark lateral stripe (vs. presence), 33-34 (vs. 34-35) vertebrae, a comparatively more developed infraorbital canal of the cephalic lateralis system with a rostral branch present (vs. absent), a nasal canal present (vs. absent) and mandibular canal complete (vs. incomplete). It is distinguished from the sympatric P. parva, by the longer head (27.5-31.9 % SL vs. 23.5-27.3), incomplete (vs. complete) lateral line, and incomplete (vs. complete) infraorbital, supraorbital and supratemporal canals of the cephalic lateralis. Pseudorasbora pumila is redescribed and a lectotype designated. © 2015 by Verlag Dr. Friedrich Pfeil, München, Germany.


Chang C.Y.,Daegu University | Lee J.,Daegu University | Smith R.J.,Lake Biwa Museum
Zootaxa | Year: 2012

Preliminary surveys of brackish and freshwater habitats in the southeast and east of South Korea produced a total of fifteen species. Ten of these species are new records for Korea, and one additional species, belonging to the genus Tanycypris, is newly described herein. Twenty-seven species of nonmarine ostracods are now reported from Korea, but this is probably only a small proportion of the actual number of species inhabiting the peninsula. The presence of Dolerocypris ikeyai Smith & Kamiya, 2006, Cryptocandona brehmi (Klie, 1934), Cryptocandona tsukagoshii Smith, 2011, Physocypria nipponica Okubo, 1990 and Vestalenula cylindrica (Straub, 1952) on the Korean Peninsula demonstrates that these species are also distributed on the continent, and are not endemic to Japan. Copyright © 2012, Magnolia Press.


Hu X.,Ocean University of China | Kusuoka Y.,Lake Biwa Museum
Acta Protozoologica | Year: 2015

Two oxytrichid freshwater ciliates, Apoamphisiella tihanyiensis (Gellért and Tamás, 1958) Foissner, 1997 and Notohymena australis (Foissner and O’Donoghue, 1990) Berger, 1999, were recorded for the first time in Lake Biwa, a 4-million-year-old lake located at the Shiga Prefecture in Japan. Their morphology was investigated based on observations of live and protargol-impregnated material. Based on the present observation and previous descriptions, A. tihanyiensis is characterized by having an elliptical body shape, yellowish cortical granules, two long frontoventral rows, enlarged frontal and transverse cirri, highly variable numbers of frontoventral, and postoral ventral cirri, and six to 11 caudal cirri arranged in three short rows. New data confirm the presence of pretransverse ventral cirri in this species. Morphologically, N. australis differs from its congeners in having the following combination of characters: greenish cortical granules, the cirrus V/2 located slight anterior to the leftmost transverse cirrus, dorsal kinety 3 almost as long as body, and seven to 10 caudal cirri arranged in three short rows. Morphogenesis in N. australis shows the same pattern as in N. apoaustralis but differs from that of other congeners in the origin of oral primordium and the formation of more than just three caudal cirri. © 2015, Jagiellonian University. All rights reserved.


A neotype is designated for the large and ecologically interesting species of Japanese earthworm, Drawida hattamimizu Hatai, 1930. Its morphological redescription is unambiguously combined with the neotype's sequence of the Cytochrome Oxidase I (COI) locus of the mitochondrial DNA, the first time an earth-worm species' type has been thus profiled. Probably it is an introduced exotic rather than a translocated native, with a patchy distribution that appears only partly defined in Japan where it is both a restricted and an endangered listed species. Brief comparison of sympatric Drawida japonica (Michaelsen, 1892) to the type-species Drawida barwelli (Beddard, 1886) - and this latter from Shiga appears as a new record for Japan - allows the diagnosis of Drawida Michaelsen, 1900 to be amended slightly. The contentious issue of molecular 'cryptic species' is queried in relation to the lack of molecular data from type-specimens, the unique name-bearing references employed in zoological nomenclature. Without such reference, neither eco-taxonomic nor genomic studies of earthworm taxa can progress. In this regard, questions are raised concerning the molecular identities and provisional divergences of cosmopolitan generotypes Allolobophora chlorotica chlorotica (Savigny, 1826), the Aporrectodea caliginosa (Savigny, 1826) species-complex sensu Blakemore (2002), and of ecotoxicological standard test-species icon Eisenia fetida fetida (Savigny, 1826). Resurrection of their respective synonyms is mooted. Resolution of relationships within and between earthworm genera and families without DNA testing of the representative type-species and type-genera is flagged as another crucial concern.


Gnathiid larvae were collected from the gill chambers of coastal sharks in southwestern Japan. Some were reared in a laboratory aquarium and successfully metamorphosed into adults. Morphological observations of the adult males identified three undescribed species, which are designated Gnathia albipalpebrata n. sp., G. parvirostrata n. sp., and G. dejimagin. sp. on the basis of their larval morphologies and pigmentation patterns. Copyright © 2014 Magnolia Press.


Toda T.,Lake Biwa Museum
Japanese Journal of Limnology | Year: 2014

The geostrophic gyre system in Lake Biwa, the largest freshwater lake in Japan, was discovered in 1926. At first, this steady fl ow system over the lake was assumed to be a direct response to the summer monsoon. It was recognized as a geostrophic current in 1960, and was the focus of intensive observations and theoretical studies until the 1980s. The main part of the system is the anticlockwise 'First Gyre', which occupies the largest circle that can be drawn in the lake s North Basin. The gyre is continuously present from May to December each year. Its disappearance in winter implies that its existence depends on stratification. Because a stratified structure stores energy as a set of kinetic and available potential energies, we can explain the origin of the gyre system both by a "wind stress curl" and a "topographic heat accumulation effect". Therefore, a quantitative evaluation of the energy budget is necessary. Although a rough description of the overall gyre system has been established previously, unresolved problems still remain concerning, e.g., the detailed formation and maintenance mechanisms of the gyre system, and its interactions with other phenomena in the lake. © 2014, Japanese Society of Limnology. All rights reserved.

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