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Freshwater fishes in the genus Paraleucogobio include two species, Paraleucogobio notacanthus and Paraleucogobio strigatus. In this study, we determined complete mitochondrial genomes of P. notacanthus and P. strigatus to clarify their phylogenetic positions. The two mitochondrial genomes showed similar gene arrangements, codon use, gene overlaps or gene intervals with the length of 16,596 bp and 16,598 bp. Our phylogeny revealed that P. notacanthus and P. strigatus were nested within Gnathopogon fishes. The findings indicate that Paraleucogobio is a junior synonym of Gnathopogon.

Migration of wild and cultivated juvenile honmoroko Gnathopogon caerulescens of from the spawning and nursery areas in Lake Biwa were investigated, both in the Ibanaiko Lagoon and its outlet to Daido River, using beam‐trawl surveys in 2013 and 2014. The study demonstrated migration of G. caerulescens from a nursery lagoon toward Lake Biwa after the juvenile stage. These findings appear to be the first direct evidence for migration of an exclusively pelagic cyprinid species from a littoral nursery to a pelagic adult habitat in a large deep lake. [ABSTRACT FROM AUTHOR]

Honmoroko Gnathopogon caerulescens is a critically endangered species and important for commercial fisheries; thus stock enhancement programs are being conducted to restore resources. We evaluated the genetic population structure of field collected samples including spawned eggs around spawning areas in Lake Biwa and the extent of genetic diversity in wild samples and hatchery stocks using sequences of mitochondrial cytochrome b gene. Pairwise Φst analysis and AMOVA clearly showed minimal population structure and haplotype network did not reveal any clear geographic pattern in Lake Biwa. It is probable that strays spawn in non-natal spawning areas, resulting in significant levels of gene flow among spawning areas. Genetic characteristics of hatchery stock F1, F2, and F3 were similar to those of wild samples in terms of haplotype diversity, nucleotide diversity and pairwise Φst values. These results indicate that the relatively high genetic diversity at its initiation was retained due to a lot of broodstock over two successive generations. Accordingly we propose that the current Honmoroko breeding method is appropriate for conserving the genetic diversity of Honmoroko and that the hatchery stock are genetically compatable for release and stock enhancement. [ABSTRACT FROM AUTHOR]

The age composition, and age- and size-dependent sex ratios of mass samples of 'Honmoroko', Gnathopogon caerulescens, were examined in Lake Biwa. The fish ranged from 0 to 2 years in age, but were mostly age 0 (97.9 %). The proportion of females was 48.6 % for age 0, 73.2 % for age 1, and 90.0 % for age 2 fish. Age 0 fish were significantly male biased, while ages 1 and 2 were significantly female biased, though the grand total showed a balanced sex ratio. The proportion of females was 48.0 % or less among age 0 fish in size classes of less than 9 cm in standard length (SL) and significantly different from a female:male ratio of 1:1 in such size classes, except for the 4-5.99 class. In size classes of 9 cm SL or greater, the proportion of females among age 0 fish was greater, more than 71.3 %, with significant differences from a balanced sex ratio for all such classes. These results suggest that G. caerulescens can be regarded as essentially an annual fish and that its spawning habits ought to result in a higher mortality for males than females, thus leading to female-biased sex ratios at ages 1 and 2. [ABSTRACT FROM AUTHOR]

The influence of hatching date on the sex ratio of wild Gnathopogon caerulescens was examined. Cohorts reared from eggs collected in the early and middle parts of the spawning season showed almost balanced sex ratios, with female bias in some cohorts. Cohorts born later in the season mostly displayed male bias, and the mean proportion of males later in the season was significantly higher than in early- and mid-season cohorts. These results indicate that the sex ratio of G. caerulescens changes with the time of breeding, increasing along with the ambient water temperature of the lake. [ABSTRACT FROM AUTHOR]

Evolution of ecomorphologically relevant traits such as body shapes is important to colonize and persist in a novel environment. Habitat-related adaptive divergence of these traits is therefore common among animals. We studied the genomic architecture of habitat-related divergence in the body shape of Gnathopogon fishes, a novel example of lake-stream ecomorphological divergence, and tested for the action of directional selection on body shape differentiation. Compared to stream-dwelling Gnathopogon elongatus, the sister species Gnathopogon caerulescens, exclusively inhabiting a large ancient lake, had an elongated body, increased proportion of the caudal region and small head, which would be advantageous in the limnetic environment. Using an F2 interspecific cross between the two Gnathopogon species (195 individuals), quantitative trait locus ( QTL) analysis with geometric morphometric quantification of body shape and restriction-site associated DNA sequencing-derived markers (1622 loci) identified 26 significant QTLs associated with the interspecific differences of body shape-related traits. These QTLs had small to moderate effects, supporting polygenic inheritance of the body shape-related traits. Each QTL was mostly located on different genomic regions, while colocalized QTLs were detected for some ecomorphologically relevant traits that are proxy of body and caudal peduncle depths, suggesting different degree of modularity among traits. The directions of the body shape QTLs were mostly consistent with the interspecific difference, and QTL sign test suggested a genetic signature of directional selection in the body shape divergence. Thus, we successfully elucidated the genomic architecture underlying the adaptive changes of the quantitative and complex morphological trait in a novel system. [ABSTRACT FROM AUTHOR]

Egg size affects larval size, growth rate, survival and fecundity with maternal fitness being maximized by a trade-off between egg size and fecundity. Production of a small number of large eggs maximizes female fitness under poor food conditions, as does a large number of small eggs under rich food conditions. Gnathopogon caerulescens (Honmoroko) spawns over a wide range of water temperature from spring to summer. Thus, we determined whether or not egg size varied with water temperature and how egg size influenced hatchling size at different water temperature. Changes in egg size strongly correlated with seasonal changes in water temperature around the lake, regardless of time and area. An experiment using eggs from the lake indicated that hatchling size has a significant positive relationship with egg size in water temperatures of 24 °C. On the other hand, a lower incubation temperature, similar to that likely to be encountered at the beginning of the spawning season, resulted in a smaller hatchling size, eggs requiring a longer time to hatch. At the beginning of the spawning season, therefore, egg size may have a lesser impact on hatching size in the natural environment of Honmoroko because of the relatively lower temperatures. Although fish larvae below a certain threshold of effective body size are generally not expected to have a high early survival rate due to, for example, a lower competitive ability or a high susceptibility to predation, seasonal egg size variation in Honmoroko may be adaptive so as to enhance the likehood of early survival by establishing an effective body size under changing water temperature conditions. [ABSTRACT FROM AUTHOR]

Diel drift patterns of larvae of the endangered cyprinid Gnathopogon caerelescens in an inlet of the Ibanaiko Lagoon, connected to Lake Biwa in Japan, were assessed in April 2012. Peak occurrence of yolk-sac larvae was within a few hours after dark. Drift of newly hatched larvae is considered to be an important biological mechanism that ensures larval dispersal and recruitment from the inlets (spawning grounds) to the lagoon which functions as a nursery ground. [ABSTRACT FROM AUTHOR]

Length-weight relationships ( LWRs) are presented for 11 species [ Acrossocheilus monticola (Günther, 1888), Squalidus wolterstorffi (Regan, 1908), Sinibrama taeniatus (Nichols, 1941), Gnathopogon herzensteini (Günther, 1896), Rhynchocypris oxycephalus (Sauvage & Dabry de Thiersant, 1874), Rhodeus lighti (Wu, 1931), Platysmacheilus nudiventris Luo, Le & Chen, 1977, Hemibagrus macropterus Bleeker, 1870, Glyptothorax fokiensis (Rendahl, 1925), Liobagrus marginatoides (Wu, 1930), Sinogastromyzon szechuanensis Fang, 1930] from the Nuoshuihe Precious Water Animal National Nature Reserve in southwestern China. Samples were collected bimonthly with trap-nets (mesh size: 5 × 5 mm; height 0.3 m; width 0.4 m; length 7 m) from 2015 to 2016. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Highlights: [•] Sertoli cell line expressing nuclear receptors was established from G. caerulescens. [•] Response to androgen and progestogen was measured by the transfection of pGL4.36. [•] 11-KT and DHP but not T and P4 worked as agonists of endogenous nuclear receptors. [•] NP but not BPA showed anti-androgenic effect on 11-KT and R1881. [•] Neither NP nor BPA showed anti-progestogenic effect on DHP. [ABSTRACT FROM AUTHOR]

We succeeded to establish cell lines from endemic fish species Honmoroko Gnathopogon caerulescens, which inhabits Lake Biwa, the third oldest lake in the world. Two cell lines designated as RMT1 and RMO1 were established from testis and ovary of G. caerulescens, respectively. These cell lines were initially cultured in Leibovitz's L-15 medium supplemented with fetal bovine serum (FBS), fish embryo extract, epidermal growth factor, and basic fibroblast growth factor. Further addition of forskolin and β-mercaptoethanol was required to establish and maintain these cell lines for more than 60 passages. RMT1 and RMO1 cells showed fibroblast- and epithelial-like morphology, respectively. From immunocytochemical staining and gene expression patterns, RMT1 cells showed a characteristic of testicular Sertoli cells and RMO1 cells did that of ovarian theca cells. Both RMT1 and RMO1 cells multiplied well in the medium supplemented with 10 % FBS at 28 °C and their minimum population doubling times were 24.4 and 28.8 h, respectively. At the 45th passage, most of the RMT1 and RMO1 cells had a hyperploid set of chromosomes (67.3 and 96.1 %, respectively). Cells with normal diploid chromosome set were not observed. RMT1 cells were transfected with an enhanced green fluorescent protein (EGFP) expression vector and human elongation factor 1 α promoter worked efficiently to express EGFP. In addition, EGFP-expressing cell lines were also established, suggesting that the cell lines could be utilized as an in vitro monitor system (biosensor) for the evaluation of endocrine disruptors which might affect gonadal function. [ABSTRACT FROM AUTHOR]

The cyprinid species of the genus Gnathopogon, exhibiting flexible morphological and ecological variation, include limnetic life forms. We examined the origin of the limnetic forms and the population divergence of the Japanese Gnathopogon species, using molecular phylogenetic and phylogeographic analyses. A Bayesian phylogenetic inference approach based on mtDNA cytochrome b sequence data revealed three major lineages in G. elongatus. One of them formed a monophyletic group with the limnetic species G. caerulescens, which is endemic to an ancient lake, Lake Biwa. The divergence of the G. caerulescens lineage was estimated to date back to the early Pleistocene. This precedes the formation of the extensive pelagic environment in the present Lake Biwa. However, the recent genetic divergence of G. caerulescens was inferred to originate in the present Lake Biwa in the late Pleistocene. Another lacustrine population in the Mikata Lakes was shown to belong to a different lineage from G. caerulescens. The majority of the population possessed unique, but non-monophyletic, haplotypes, suggesting a short evolutionary history. One of the cryptic lineages of G. elongatus discovered in the Ina Valley, the lower area of Lake Suwa, might be related to the extinct lacustrine subspecies G. elongatus suwae, which has been replaced by introduced congeners. The previous and ongoing introductions of Gnathopogon fishes would have produced genetic disturbance to the indigenous populations. [ABSTRACT FROM AUTHOR]

Background: The construction of linkage maps is a first step in exploring the genetic basis for adaptive phenotypic divergence in closely related species by quantitative trait locus (QTL) analysis. Linkage maps are also useful for comparative genomics in non-model organisms. Advances in genomics technologies make it more feasible than ever to study the genetics of adaptation in natural populations. Restriction-site associated DNA (RAD) sequencing in next-generation sequencers facilitates the development of many genetic markers and genotyping. We aimed to construct a linkage map of the gudgeons of the genus Gnathopogon (Cyprinidae) for comparative genomics with the zebrafish Danio rerio (a member of the same family as gudgeons) and for the future QTL analysis of the genetic architecture underlying adaptive phenotypic evolution of Gnathopogon. Results: We constructed the first genetic linkage map of Gnathopogon using a 198 F2 interspecific cross between two closely related species in Japan: river-dwelling Gnathopogon elongatus and lake-dwelling Gnathopogon caerulescens. Based on 1,622 RAD-tag markers, a linkage map spanning 1,390.9 cM with 25 linkage groups and an average marker interval of 0.87 cM was constructed. We also identified a region involving female-specific transmission ratio distortion (TRD). Synteny and collinearity were extensively conserved between Gnathopogon and zebrafish. Conclusions: The dense SNP-based linkage map presented here provides a basis for future QTL analysis. It will also be useful for transferring genomic information from a "traditional" model fish species, zebrafish, to screen candidate genes underlying ecologically important traits of the gudgeons. [ABSTRACT FROM AUTHOR]

The second gnathopods of caprellid male amphipods are larger than the ones observed in females. The second gnathopods are armed with a propodus or tooth that is associated with a poison producing gland, by which male-male Contests lead to fatal Outcomes. Here we observed the ultrastructure of the second gnathopods by scanning electron microscopy and compared the relationship between the number of pores in the poison tooth and body length among the males of four caprellid species: Caprella acanthogaster, C. bispinosa, C. scaura, and C. penantis. All species possess pores on the poison tooth, and the number of pores increased with body size. The number of pores also differed among specimens of the four species. Furthermore, in males of three caprellid species, except for C. penantis, we found additional pores at the tip of the dactylus of second gnathopods. The number of pores on the tip of the dactylus did not increase with body length, and the average number of them differed among the three species. Although it is not known if venom is released from the pores of both structures, larger individuals that possess more pores on the second gnathopods could have a competitive advantage in male-male competition. [ABSTRACT FROM AUTHOR]

Primers were developed for single-tube genotyping of four genera, Cyprinus, Carassius, Gnathopogon, and Ischikauia. Most of the six species in Lake Biwa belonging to these four genera (one is a native Japanese common carp) are endangered, and two of the six are important fisheries resources. However, many aspects of their reproductive ecology are unclear, because these species spawn similar looking eggs on similar substrates during the same time of year. The molecular method developed here enabled efficient and cost-effective genus-level identification of such eggs, providing a breakthrough for developing effective conservation strategies for these species. [ABSTRACT FROM AUTHOR]

The sex ratios of the offspring of males from broods of honmoroko Gnathopogon caerulescens that displayed thermolabile sex determination (TSD), and those from eggs collected from the wild, strongly suggest that the combination of parents plays an important supplementary role in TSD in this species. The proportion of females in all broods from eight pairings of fish captured in the field decreased significantly at 30°C compared to 20°C, and one brood was entirely female at the lower temperature. These results suggest that phenotypic males (XX-males) exist in nature, probably as a result of sex change from genetic females caused by TSD. Sex ratios in relation to water temperature fall into five patterns, two of which seem to result from normal pairings of XX-females and XY- males, and from pairings of XX-males and XX-females with non-thermosensitivity. Two other patterns are thought to result from the same types of pairing, but with thermosensitivity. The last pattern, which shows male bias at both low and high temperature, is not explained only by the combination of genotypic sex determination (XX/XY) and TSD. Fluctuating temperatures close to natural conditions showed little potential to masculinize broods laid in the field between April and early June. However, the sex ratios of fish spawned in early June showed male bias at low and high temperatures. The sex determination mechanism in G. caerulescens may involve the interaction between temperature and sex-determining genetic factors, and the relative importance of each component differs with breeding season. [ABSTRACT FROM AUTHOR]

The relationships between environmental variables, distribution of freshwater fishes and their diet were investigated at 40 sites on irrigation ditches for rice fields in central Japan. Multivariate analyses showed that fish species richness and diversity in ditches was high when fishes were able to easily invade the rice fields. Natural stream beds not covered by concrete had greater total number and biomass of fishes in irrigation ditches. The connection between ditches and rice fields was of secondary importance. Canonical correlation analysis indicated that the two principal fish community variables, abundance and diversity, were respectively represented by the presence of the minnow, Gnathopogon elongatus elongatus, and the absence of the loach, Misgurnus anguillicaudatus. Most fishes in the irrigation ditches predominantly preyed upon aquatic insects such as ephemeropteran nymphs, chironomid larvae and trichopteran larvae, but aerial insects and benthic algae were also fed upon by a few species. Small fishes (<4 cm SL) preyed more on chironomid and less on trichopteran larvae than large (≥4 cm SL) fishes. The diet overlap between species was extremely high for small fishes in ditches weakly connected with rice fields. The recent changes in rice fields and irrigation ditches to increase production efficiency has led to a decrease in fish diversity. For the coexistence of rice production and fish diversity in rice areas, a new irrigation system, where fishes can easily invade rice fields and where plenty of invertebrates are available for fishes, should be developed. [ABSTRACT FROM AUTHOR]

Freshwater fishes in the genus Paraleucogobio include two species, Paraleucogobio notacanthus and Paraleucogobio strigatus. In this study, we determined complete mitochondrial genomes of P. notacanthus and P. strigatus to clarify their phylogenetic positions. The two mitochondrial genomes showed similar gene arrangements, codon use, gene overlaps or gene intervals with the length of 16,596 bp and 16,598 bp. Our phylogeny revealed that P. notacanthus and P. strigatus were nested within Gnathopogon fishes. The findings indicate that Paraleucogobio is a junior synonym of Gnathopogon. [ABSTRACT FROM AUTHOR]

The complete mitochondrial genome ofGnathopogon taenielluswas first determined in this study. It is 16,596 bp in length, contains 13 protein-coding genes, 2 rRNA genes, 22 tRNA genes and one control region in the typical vertebrate gene order and transcriptional direction. There are total of 29 bp short overlaps and 34 bp non-coding intergenic spacers were found in the mitogenome. Overall nucleotide base composition of light strand is 29.3% A, 25.8% C, 17.9% G and 27.0% T. Two start codons (ATG and GTG) and two stop codons (TAG and TAA/T) were used in the protein-coding genes. The origin of light strand replication (OL) was identified between tRNAAsnand tRNACysgenes and could fold a hairpin structure. The nucleotide composition of control region is 31.8% A, 20.9% C, 14.0% G and 33.3% T. [ABSTRACT FROM AUTHOR]

The complete mitochondrial genome was sequenced from one of the endemic freshewater gudgeons (Gnathopogon polytaenia) in China. The mitochondrial genome sequence was 16,594 bp in size, and the gene order and contents were identical with the congeneric speciesG. strigatusandG. elongatus.Six genes (COII, ATP6, COIII, ND3, ND4, Cytb) had an incomplete stop codon. Base composition of the genome is A (29.1%), T (26.9%), C (25.9%) and G (18.1%) with an A + T rich feature (56%) as that of other vertebrate mitochondrial genomes. [ABSTRACT FROM AUTHOR]

The complete mitochondrial genome ofGnathopogon argentatuswas determined to be 16,607 bp long circular molecule with a typical gene arrangement of vertebrate mitochondrial DNA. The complete mitochondrial genome ofG. argentatusis 16,607 bp in length with 56.02% AT content, including 13 protein-coding genes, 22 tRNA genes, 2 rRNA genes and 1 control region. The complete mitochondrial genome ofG. argentatuswas obtained for the first time and would play an important role in population structure and conservation genetic studies. [ABSTRACT FROM AUTHOR]

Freshwater fishes in the genus Paraleucogobio include two species, Paraleucogobio notacanthus and Paraleucogobio strigatus . In this study, we determined complete mitochondrial genomes of P. notacanthus and P. strigatus to clarify their phylogenetic positions. The two mitochondrial genomes showed similar gene arrangements, codon use, gene overlaps or gene intervals with the length of 16,596 bp and 16,598 bp. Our phylogeny revealed that P. notacanthus and P. strigatus were nested within Gnathopogon fishes. The findings indicate that Paraleucogobio is a junior synonym of Gnathopogon ., Competing Interests: The authors report no conflict of interest. The authors are also responsible for the content and writing of the paper., (© 2019 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group.)