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Bitterling fish species (subfamily: Acheilognathinae) are endangered in Japan due to habitat loss. The decline of freshwater mussels also enhances the decrease of bitterlings because bitterlings lay eggs in the gills of freshwater mussels. Furthermore, loss of unionid mussels causes hybridization between bitterling species. This study aims to analyze the frequency of hybridization between congeneric species of bitterlings—Tanakia lanceolata and Tanakia limbata—at a well‐preserved site, where both species occur naturally and compare this with other regions more severely impacted by human intervention. One part of the irrigation streams of the Asahi River System, Okayama, is inhabited by a natural monument species of Japan, a benthic cobitid, Parabotia curtus, and therefore, the natural substratum and the structurally heterogeneous stream banks are maintained. We collected Tanakia individuals and surveyed mussel density at this well‐preserved site. We also developed six nuclear single‐nucleotide polymorphism (SNP) markers on different chromosomes to distinguish T. lanceolata and T. limbata. These SNP markers effectively determined individuals as being either one of these species or a hybrid. Based on genotyping, eight individuals were determined to be hybrids, whereas 90 and 173 individuals were determined as purebreds of T. lanceolata and T. limbata, respectively. The proportion of hybrid individuals was 3.0% and was relatively low compared to other regions. In addition, five species of unionids were densely distributed in this stream. Prezygotic isolation between sympatric T. lanceolata and T. limbata was established at this well‐preserved site, where unionid mussels are densely populated and provide enough breeding substrate for both species. [ABSTRACT FROM AUTHOR]

Paratanakia chii is a bitterling fish of the genus Paratanakia, subfamily Acheilognathinae and family Cyprinidae. The mitochondrial DNA sequence of P. chii is reported in this paper. The complete mitochondrial genome of P. chii is 16,575 bp in length, including 13 protein-coding genes (PCGs), 2 rRNA genes, 22 tRNA genes, and 1 displacement loop (D-loop). The genome sequence is consistent with those of most other carp. The majority of PCGs have AT- (Met) start codons and TA- end codons. The A + T contents of the genome, PCGs, transfer RNAs (tRNAs), and ribosomal RNAs (rRNAs) are 56.92%, 58.07%, 56.34%, and 54.21%, respectively. Phylogenetic analysis showed that P. chii is most closely related to Tanankia himantegus. These data will benefit relative ecological and phylogenetic studies.

Bitterling embryos compete with the host mussel for oxygen, and bitterling can be considered as parasites of mussels (Reichard et al., [12]). Mussels that co-occur with bitterlings have evolved a response of ejecting bitterling eggs and also show morphological and behavioral responses that can limit bitterling spawning success (Kitamura et al., [7]). Bitterling egg shape, therefore, appears to rapidly evolve in response to selection pressure from adaptations of host mussels against bitterling parasitism, generating conspicuous variation in egg shape and size. [Extracted from the article]

Paratanakia chii is a bitterling fish of the genus Paratanakia, subfamily Acheilognathinae and family Cyprinidae. The mitochondrial DNA sequence of P. chii is reported in this paper. The complete mitochondrial genome of P. chii is 16,575 bp in length, including 13 protein-coding genes (PCGs), 2 rRNA genes, 22 tRNA genes, and 1 displacement loop (D-loop). The genome sequence is consistent with those of most other carp. The majority of PCGs have AT- (Met) start codons and TA- end codons. The A + T contents of the genome, PCGs, transfer RNAs (tRNAs), and ribosomal RNAs (rRNAs) are 56.92%, 58.07%, 56.34%, and 54.21%, respectively. Phylogenetic analysis showed that P. chii is most closely related to Tanankia himantegus. These data will benefit relative ecological and phylogenetic studies. [ABSTRACT FROM AUTHOR]

Three new species of Gyrodactylus are described from three species of bitterling in Donghu Lake, China: Gyrodactylus ocellorhodei n. sp. from Rhodeus ocellatus ; G. sinenorhodei n. sp. from Rhodeus sinensis ; and G. acheilorhodei n. sp. from Acheilognathus macropterus. All the three new species showed similar opisthaptor morphology, especially the marginal hooks: all had a slender and perpendicular sickle shaft, and flat sickle base with distinct heel and inner arch which was different from the G. rhodei -group species parasitic on bitterling. Multivariate analyses based on hamulus and marginal hooks suggested that these three new species cannot be completely distinguished, despite some morphology divergence observed in certain less reliable morphometric features, such as hamulus root length, ventral bar total length and process shape. These three new species shared an identical 18S ribosomal RNA gene sequence, while the variation in the Internal Transcribed Spacers (ITS1-ITS2) sequence among them (8.4–11.2%, K2P) far exceeded the 1% ITS sequence difference that had been suggested as a threshold for species delimitation of Gyrodactylus. Phylogenetic analysis based on ITS1-ITS2 showed that all these sequenced Gyrodactylus spp. parasitic on the subfamily Acheilognathinae host formed a monophyletic group. However, a clear differentiation (18.9–20.9%, K2P of ITS1-ITS2) could be found between the subgroup from China (G. ocellorhodei n. sp., G. sinenorhodei n. sp. and G. acheilorhodei n. sp.) and that from Europe (G. rhodei). [Display omitted] • Three new species of Gyrodactylus are described from bitterling in Donghu Lake, China. • The identified species had distinct ventral bar features, although their hamulus and marginal hooks were similar. • Gyrodactylus spp. parasitic on bitterling formed a monophyletic group. [ABSTRACT FROM AUTHOR]

The life history and reproductive ecology of an autumn‐spawning bitterling Acheilognathus typus were studied under natural and experimental conditions. In the study pond, the embryos of A. typus emerged from mussels in May and grew rapidly until August, whereas overwintered age‐1 fish grew slowly. Adult A. typus in the pond was smaller (32–47 mm in standard length) than they were in other habitats and mainly spawned in smaller mussels. The number of A. typus embryos in mussels was negatively correlated with the shell length of the mussel, and a lower number of embryos were observed in larger mussels (over 110 mm in shell length). In the mussel size‐choice experiment conducted in an enclosure, smaller A. typus selected smaller mussels, and larger A. typus selected larger mussels for spawning. In some cases, smaller A. typus spawned in larger mussels and the number of spawned eggs ejected increased by over four times compared with other cases. These results of the enclosure experiment explained the lower number of embryos in larger mussels in the study pond. In addition, reproductive traits such as ovipositor length and the number of ovulated eggs of female A. typus, which are considered to contribute to their size‐dependent host utilization, were positively correlated with their standard length. Because A. typus is geologically or seasonally isolated from other bitterling species, this size‐dependent host utilization contributes to a reduction in intraspecies rather than interspecies competition. [ABSTRACT FROM AUTHOR]

Rhodeus cyanorostris Li, Liao & Arai, 2020 is a freshwater fish that is endemic to China and restricted to Chengdu City in Sichuan Province. This study is the first to sequence and characterize the complete mitochondrial genome of R. cyanorostris. The mitogenome of R. cyanorostris is 16580 bp in length, including 13 protein-coding genes, two rRNA genes, 22 tRNA genes, and a control region (D-loop). The base composition of the sequence is 28.5% A, 27.6% C, 26.4% T, and 17.5% G, with a bias toward A+T. The genome structure, nucleotide composition, and codon usage of the mitogenome of R. cyanorostris are consistent with those of other species of Rhodeus. To verify the molecular phylogeny of the genus Rhodeus, we provide new insights to better understand the taxonomic status of R. cyanorostris. The phylogenetic trees present four major clades based on 19 mitogenomic sequences from 16 Rhodeus species. Rhodeus cyanorostris exhibits the closest phylogenetic relationship with R. pseudosericeus, R. amarus, and R. sericeus. This study discloses the complete mitochondrial genome sequence of R. cyanorostris for the first time and provides the most comprehensive phylogenetic reconstruction of the genus Rhodeus based on whole mitochondrial genome sequences. The information obtained in this study will provide new insights for conservation, phylogenetic analysis, and evolutionary biology research. [ABSTRACT FROM AUTHOR]

• The first report of complete mitochondrial genome of Acheilognathus gracilis. • A. gracilis shows a unusual AT-skew with slightly negative. • Unusual AT-skew in nd5 implies unique strategy of adaptive evolution in A. gracilis. • The monophyly of Acheilognathus and the paraphyly of Rhodeus - Tanakia are supported. Acheilognathus gracilis, a bitterling species, distribute in lower reaches of Yangtze River. They are identified as the top-priority bitterling species for conservation as having high evolutionary distinctiveness and are at risk of extinction. In present study, we first sequenced the complete mitogenome of A. gracilis and analyzed its phylogenetic position using 13 PCGs. The A. gracilis mitogenome is 16,774 bp in length, including 13 protein-coding genes, 2 ribosomal RNAs, 22 transfer RNAs, a control region and the origin of the light strand replication. The overall base composition of A. gracilis in descending order is T 27.9 %, A 27.7 %, C 26.1 % and G 18.3 %, shows a unusual AT-skew with slightly negative. Further investigation revealed A. gracilis uses excess T over A in NADH dehydrogenase 5 (nd5), whereas the most of other bitterlings are biased toward to use A not T, implying there is likely to be unique strategy of adaptive evolution in A. gracilis. We also compared 13 PCGs of 30 bitterling mitogenomes and the results exhibit highly conservative. Phylogenetic trees constructed by 13 PCGs strongly support the monophyly of Acheilognathus and the paraphyly of Rhodeus and Tanakia. Current results will provide valuable information for follow-up research on conservation of species facing with serious population decline and can provide novel insights into the phylogenetic analysis and evolutionary biology research. [ABSTRACT FROM AUTHOR]

Bitterling fishes (Subfamily: Acheilognathinae) spawn in the gills of living freshwater mussels and obligately depend on the mussels for reproduction. On the Matsuyama Plain, Japan, populations of unionid mussels—Pronodularia japanensis, Nodularia douglasiae, and Sinanodonta lauta—have decreased rapidly over the past 30 years. Simultaneously, the population of a native bitterling fish, Tanakia lanceolata, which depends on the three unionids as a breeding substrate, has decreased. Furthermore, a congeneric bitterling, Tanakia limbata, has been artificially introduced, and hybridisation and genetic introgression occur between them. Here, we hypothesised that decline of the unionids has enhanced this invasive hybridisation through competition for the breeding substrate.Three study sites were set in three streams on the Matsuyama Plain. We collected adult bitterling fishes (native T. lanceolata, introduced T. limbata, and foreign Rhodeus ocellatus ocellatus) once a week from April to October 2013 to measure their densities in streams and to examine seasonal differences in female ovipositor length, which elongates in the breeding season. Simultaneously, we set quadrats and captured unionids and measured environmental conditions. Each unionid individual was kept separately in its own aquarium to collect ejected bitterling eggs/larvae. Tanakia eggs and larvae were genotyped using six microsatellite markers and the mitochondrial cytochrome b gene.Introduced T. limbata was more abundant, had a longer breeding period, and produced more juveniles than native T. lanceolata. Hybrids between the two species occurred at all sites, and in total 101 of the 837 juveniles genotyped were hybrids. The density of P. japanensis was low, at most 0.42 individuals/m2. Nodularia douglasiae and S. lauta have nearly or totally disappeared from these sites. Hybrid clutches of Tanakia species occurred more frequently where the local density of P. japanensis was low. Mussels were apparently overused and used simultaneously by three species of bitterlings.Decline of freshwater unionid populations has enhanced hybridisation of native and invasive bitterling fishes through increasing competition for breeding substrate. We showed that rapid decline of host mussel species and introduction of an invasive congener have interacted to cause a rapid decline of native bitterling fish.Degradation of habitat and the introduction of invasive species interact to cause a cascade of extinctions in native species. In our study, obligate parasite species are threatened because the host species are disappearing, which means there is a serious threat of coextinction. [ABSTRACT FROM AUTHOR]

The bitterling Tanakia lanceolata is a primary freshwater fish with wide distribution range in Japan; therefore, analysis of this species will yield much information on the formation of Japanese freshwater fish fauna. However, populations of this species are threatened by several human activities. To reveal the genetic population structure of T. lanceolata and the process of its formation, as well as its genetic status, we conducted phylogenetic analyses and estimated divergence times based on partial sequences of the mitochondrial DNA cytochrome b gene, using specimens collected across the distribution range. The results of the analysis showed that Japanese T. lanceolata is monophyletic and consists of seven local population groups that diverged from the Late Pliocene to the Middle Pleistocene. The population structure in western Japan was similar to that of other freshwater fishes (e.g., separation by the Suzuka Mountains), although there were several differences in population boundaries and the presence/absence of a secondary contact zone. The Central Highlands in central Honshu are the primary, or at least the most effective, geological barrier responsible for population divergence in Japanese freshwater fish species. However, the small genetic differentiation of the T. lanceolata population between the western and eastern sides of the Central Highlands suggested recent dispersal and gene flow across the region after uplift of the highlands. The genetic population structure indicated extensive genetic disturbance in the Kanto Region. Our results provide information on the formation process of the Japanese freshwater fish fauna, which could aid conservation efforts toward T. lanceolata. [ABSTRACT FROM AUTHOR]

Parasitic infections elicit host defences that pose energetic trade-offs with other fitness-related traits. Bitterling fishes and unionid mussels are involved in a two-way parasitic interaction. Bitterling exploit mussels by ovipositing into their gills. In turn, mussel larvae (glochidia) develop on the epidermis and gills of fish. Hosts have evolved behavioural responses to reduce parasite load, suggesting that glochidia and bitterling parasitism are costly. We examined the energetic cost of parasitism on both sides of this relationship. We used intermittent flow-through respirometry to measure (1) standard metabolic rate (SMR) of individual duck mussels Anodonta anatina (a common bitterling host) before and during infection by embryos of the European bitterling Rhodeus amarus, and (2) SMR and maximum oxygen uptake (MO2max) of individual R. amarus before and during infection with glochidia of the Chinese pond mussel Sinanodonta woodiana (a mussel species that successfully infects bitterling). As predicted, we observed an increase in mussel SMR when infected by bitterling embryos and an increased SMR in glochidia-infected bitterling, though this was significantly mediated by the time post-infection. Contrary to our predictions, glochidia infection did not impair MO2max and the number of glochidia attached to gills positively (rather than negatively) correlated with MO2max. The results suggest that tolerance is the prevailing coping mechanism for both fish and mussels when infected, while resistance mechanisms appear to be confined to the behavioural level. [ABSTRACT FROM AUTHOR]

Abstract Sinorhodeus microlepis (S. microlepis) is recently described as a new species and represents a new genus Sinorhodeu of the subfamily Acheilognathinae. In this study, we first sequenced the complete mitogenome of S. microlepis and compared with the other 29 bitterling mitogenomes. The S. microlepis mitogenome is 16,591 bp in length and contains 37 genes. Gene distribution pattern is identical among 30 bitterling mitogenomes. A significant linear correlation between A+T% and AT-skew were found among 29 bitterling mitogenomes, except S. microlepis shows unusual AT-skew with slightly negative in tRNAs and PCGs. Bitterling mitogenomes exhibit highly conserved usage bias of start codon, relative synonymous codons and amino acids, overlaps and non-coding intergenic spacers. Phylogenetic trees constructed by 13 PCGs strongly support the polyphyly of the genus Acheilognathus and the paraphyly of Rhodeus and Tanakia. Together with the unusual characters of S. microlepis mitogenomes and phylogenetic trees, S. microlepis should be a sister species to the genus Rhodeu that might diverge about 13.69 Ma (95% HPD: 12.96–14.48 Ma). Highlights • The first report of complete mitochondrial genome of S. microlepis. • Unusual AT-skew and base compositions in S. microlepis mitogenome. • Highly conserved overlaps and non-coding intergenic spacers among bitterling mitogenomes. • S. microlepis should be a sister species to the genus Rhodeu that might diverge about 13.69 Ma. [ABSTRACT FROM AUTHOR]

The infection status with Clonorchis sinensis metacercariae (CsMc) was examined in freshwater fishes from Yangcheon (a branch of Gyeongho-gang), which is located in Sancheong-gun, Gyeongsangnam-do, the Republic of Korea. Total 2,201 fishes in 26 species were examined by the artificial digestion method through 7 years. CsMc were detected in 1,171 (53.2%) fishes in 21 spp. (80.8%) and their density was 85 per fish infected. Total 532 (99.6%) out of 534 Pungtungia herzi (index fish) examined were infected with 147 CsMc per fish infected. Metacercarial densities in this fish were highest in 2015 (179 CsMc), followed by 2012 (168), 2013 (152), 2016 (145), 2014 (114), and 2017 (89) respectively. In the gobioninid fish group, i.e., P. herzi, Sarcocheilichthys spp., Squalidus spp., Pseudogobio esocinus, Hemibarbus longirostris, and Hemibarbus labeo, 841 (92.7%) fishes were infected with 117 CsMc per fish infected. Total 250 (54.7%) acheilognathinid fish (bitterlings), Acheilognathus spp. and Acanthorhodeus spp. were infected with 5.8 CsMc. In the rasborinid fish (chubs) group, i.e., Zacco platypus, Zacco temminckii, and Zacco koreanus, 77 (13.7%) out of 563 fish examined were infected with 2.4 CsMc in average. The susceptibility indices of CsMc were 49.09 in the overall positive fish group, 104.15 in the gobioninid group, 3.17 in the acheilognathinid group and 0.35 in the rasborinid fish group respectively. Only 1 CsMc was detected in 3 fish species, Coreoperca herzi, Channa argus, and Lepomis macrochirus, respectively. Conclusively, it was confirmed that CsMc are moderately prevalent in fishes from Yangcheon in Sancheon-gun, Gyeongsangnam-do, Korea. [ABSTRACT FROM AUTHOR]

Bitterling fishes and unionid mussels are involved in a two-sided co-evolutionary association. On the one side, bitterling exploit unionids by ovipositing in their gills. On the other side, unionids develop via a larval stage (glochidium) that attaches to fish gills. Both interactions are parasitic and expected to have negative consequences for the host. Here, we examine the effects of this association on the metabolic rates of mussel and fish hosts by measuring oxygen uptake rates (MO2). Measurements were performed on two widespread and broadly coexisting species, namely the rose bitterling Rhodeus ocellatus and Chinese pond mussel Sinanodonta woodiana. As predicted, we observed an increase in routine MO2in mussels parasitized by bitterling, but only when hosting early stages of bitterling embryos that reside in the interlamellar space of the gills and obstruct water circulation. Hosting later-stage bitterling embryos (that reside in the suprabranchial cavity outside the host gills) was not associated with a higher routine MO2. We did not observe an acute negative effect of glochidial infestations on maximal oxygen uptake rate (MO2max), but glochidia-infested bitterling showed consistently lower oxygen consumption rates during recovery from MO2max. Our results suggest that acute costs of this mutually parasitic relationship might be mitigated, at least in part, by adaptations to limit infestation rates. [ABSTRACT FROM AUTHOR]

The infection status of Clonorchis sinensis metacercariae (CsMc) was examined in freshwater fish from a highly prevalent site, Wicheon (a branch of Nakdong-gang), which is located in Gunwi-gun, Gyeongsangbuk-do, the Republic of Korea. Total 1,162 fish in 32 species were examined by the artificial digestion method through 6 years. CsMc were detected in 720 (67.5%) out of 1,067 fish (26 spp.) and their density was 610 per fish infected. In the susceptible gobioninid fish group, i.e., Pungtungia herzi, Squalidus gracilis majimae, Squalidus japonicus coreanus, Sarcocheilichthys variegatus wakiyae and Pseudorasbora parva, all of 323 fish were infected with an average of 1,310 CsMc. Total 23 (95.8%) gobioninid fish, i.e., Pseudogobio esocinus, Abbottina springeri, Hemibarbus longirostris, Microphysogobio koreensis, and Microphysogobio jeoni, were infected with 127 CsMc in average. In the acheilognathinid fish (bitterlings) group, the prevalence was 77.0%, and the density was 50 CsMc per fish infected. In the rasborinid fish (chubs) group, i.e., Zacco platypus, Zacco temminckii, Zacco koreanus, and Opsariichthys uncirostris amurensis, 147 (36.5%) out of 403 fish examined were infected with 15 CsMc in average. The susceptibility indices of CsMc were 412 in the overall positive fish group, 1,310 in the gobioninid group-1, 122 in the gobioninid group-2, 38.5 in the acheilognathinid group, and 5.5 in the rasborinid fish group. Conclusively, it was confirmed that CsMc are highly prevalent in fish from Wicheon, and their infection tendency varied according to the subfamily groups in Cyprinidae fish hosts. [ABSTRACT FROM AUTHOR]

Paratanakia chii is a bitterling fish of the genus Paratanakia , subfamily Acheilognathinae and family Cyprinidae. The mitochondrial DNA sequence of P. chii is reported in this paper. The complete mitochondrial genome of P. chii is 16,575 bp in length, including 13 protein-coding genes (PCGs), 2 rRNA genes, 22 tRNA genes, and 1 displacement loop (D-loop). The genome sequence is consistent with those of most other carp. The majority of PCGs have AT- (Met) start codons and TA- end codons. The A + T contents of the genome, PCGs, transfer RNAs (tRNAs), and ribosomal RNAs (rRNAs) are 56.92%, 58.07%, 56.34%, and 54.21%, respectively. Phylogenetic analysis showed that P. chii is most closely related to Tanankia himantegus . These data will benefit relative ecological and phylogenetic studies., Competing Interests: No potential conflict of interest was reported by the author(s)., (© 2023 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group.)

Somjin bitterling ( Tanakia somjinensis ), an endemic cyprinid on the Korean Peninsula, is critically endangered with only a few small populations found in limited areas in a single drainage, raising concerns that this species has likely suffered low levels of genetic variability. In the current study, 23 polymorphic microsatellite markers were developed using Illumina paired-end sequencing for quantification of the genetic diversity in this species and to determine their amplification efficiency in other bitterling species. A total of 50 somjin bitterlings collected from two localities were genotyped using these 23 loci. This species showed a remarkably high level of genetic variability, with an average number of alleles per locus of 17.30 and mean observed and expected heterozygosity values of 0.758 and 0.802, respectively. Our relatedness analyses for all pairs of individuals clearly indicated that the two somjin bitterling populations were completely outbred. No signature of drastic demographic decline was detected using our analytical methods. Many of our loci were validated as successfully transferable within and between genera and could potentially be used for genetic and demographic studies in other bitterling species. [ABSTRACT FROM AUTHOR]

Bitterlings are relatively small cypriniform species and extremely interesting evolutionarily due to their unusual reproductive behaviors and their coevolutionary relationships with freshwater mussels. As a group, they have attracted a great deal of attention in biological studies. Understanding the origin and evolution of their mating system demands a well-corroborated hypothesis of their evolutionary relationships. In this study, we provide the most comprehensive phylogenetic reconstruction of species relationships of the group based on partitioned maximum likelihood and Bayesian methods using DNA sequence variation of nuclear and mitochondrial genes on 41 species, several subspecies and three undescribed species. Our findings support the monophyly of the Acheilognathidae. Two of the three currently recognized genera are not monophyletic and the family can be subdivided into six clades. These clades are further regarded as genera based on both their phylogenetic relationships and a reappraisal of morphological characters. We present a revised classification for the Acheilognathidae with five genera/lineages: Rhodeus , Acheilognathus (new constitution), Tanakia (new constitution), Paratanakia gen. nov., and Pseudorhodeus gen. nov. and an unnamed clade containing five species currently referred to as “ Acheilognathus ”. Gene trees of several bitterling species indicate that the taxa are not monophyletic. This result highlights a potentially dramatic underestimation of species diversity in this family. Using our new phylogenetic framework, we discuss the evolution of the Acheilognathidae relative to classification, taxonomy and biogeography. [ABSTRACT FROM AUTHOR]

In some taxa, males perform multiple ejaculations, which may function in sperm competition or in maintaining a baseline density of spermatozoa in the female reproductive tract to ensure fertilization, a process that has been termed 'topping up'. We investigated the function of multiple ejaculations in two species of bitterling, the European bitterling ( Rhodeus amarus) and Chinese rose bitterling ( Rhodeus ocellatus). Bitterling oviposit in living freshwater mussels, with fertilization taking place within the mussel gill cavity. Thus, although fertilization is external, the mussel is analogous to the female reproductive tract in an internally fertilizing species. We measured the frequency of ejaculations and mussel inspections by individual males of two bitterling species in 28 replicated mesocosms and examined focal male responses to rival ejaculations and the presence of females in spawning condition. We used a model of ejaculatory behaviour to simulate the temporal abundance of spermatozoa in mussels. Male R. amarus exhibited high rates of ejaculation and inspection of the siphons of mussels and increased their ejaculation rate in response to the presence of females in spawning condition. Rhodeus ocellatus showed lower overall rates of ejaculation, but significantly elevated ejaculation rate in response to rival ejaculations. The ejaculatory strategy of R. amarus is one that maintains a minimum level of spermatozoa in mussels, which is elevated when the probability of oviposition increases. In contrast, R. ocellatus engages more directly in sperm competition with rivals. We discuss these results in the context of the function of multiple ejaculations and male mating tactics. [ABSTRACT FROM AUTHOR]

Geographic isolation and colonization events have been considered complimentary historical processes in shaping the contemporary structure of regional biotas and taxonomic diversity. Accordingly, insight regarding vicariance and geodispersal might be gained by the analysis of phylogenetic pattern of related but geographically isolated taxa. Here, we examined endangeredRhodeus pseudosericeusin the Korean Peninsula based on mitochondrial cytochromebsequences to provide information regarding the evolutionary origin of Amur-European bitterlings,Rhodeus sericeusandRhodeus amarus. Our data and the contemporary distribution ofR. pseudosericeusindicate that founding individuals have colonized the western coast of the Korean Peninsula via the paleo-Huang He River and since been subdivided into populations isolated by drainage formation. Our phylogenetic analyses indicated that it was likelyR. pseudosericeushad a sister relationship to theR. sericeus–amaruscomplex, indicating that theR. sericeus–amarusclade originated from the dispersal of eitherR. pseudosericeusor its ancestral lineage. The geodispersal scenario based on our phylogenetic analyses supports the previous hypothesis that the Amur River likely created confluences with some tributaries of the paleo-Huang He River. Overall, the present study offers new insight into the taxonomic entity ofR. pseudosericeusand a more comprehensive understanding of the phylogeographic history ofR. sericeusand European bitterling lineages. [ABSTRACT FROM PUBLISHER]

Sperm competition occurs when the spermatozoa of one male coincide with those of another to fertilise the same eggs. In some taxa males perform multiple ejaculations, which may function in sperm competition or in maintaining a baseline density of spermatozoa in the female reproductive tract to ensure fertilisation, a process that has been termed 'topping up'. We investigated multi-ple ejaculations in the European bitterling (Rhodeus amarus), a freshwater fish that oviposits in freshwater mussels. We quantified spermatozoa in the mussel mantle cavity following ejaculation, and measured sperm motility parameters of males adopting different mating tactics. Following ejaculation spermatozoa density in the mussel increased linearly, peaked after 30 s, and then de-clined exponentially. Spermatozoa motility parameters did not differ between male mating tactics. We parameterised a model of sperm competition for R. amarus, which accurately predicted male fertilisation probability. We discuss these results in the context of multiple ejaculations and male mating tactics. [ABSTRACT FROM AUTHOR]

The distributions of seven bitterling species and subspecies- Tanakia lanceolata, T. limbata, Acheilognathus tabira nakamurae, A. rhombeus, Rhodeus ocellatus kurumeus, R. ocellatus ocellatus, and R. atremius atremius-in northern Kyushu were predicted using generalized linear models (GLMs) in order to provide information helpful for conserving native bitterlings and preventing the expansion of alien bitterling species. Predictions were made according to the following procedure: (1) a set of GLMs for each species was formulated using environmental data from 710 sites that were derived using digital maps and GIS software, from which the best fit model for each species was selected using the Akaike information criterion for predicting the fish occurrence, (2) model performance was evaluated based on the receiver-operating characteristics (ROC) analysis using occurrence and environmental data from 362 sites, and (3) potential distributions of the bitterling were analyzed using the best fit models and environmental data for 1,272 sites, of which 200 data points without occurrence data were prepared. The best fit models revealed that 4-6 environmental factors were important in predicting seven bitterling distributions, which was supported by the area under the ROC curve (AUC) values of these fishes ranging from 0.753 to 0.927. The AUC values in model evaluation were significantly greater than 0.5 for six fishes, suggesting the moderate accuracies of these best fit models for predicting the fish distributions. These predictive models can be used for evaluating potential native bitterling richness and the potential distribution expansion of an alien subspecies. [ABSTRACT FROM AUTHOR]

Ecologically specialized species may be more susceptible to anthropogenic impacts than generalist species. Japan's native bitterlings (subfamily Acheilognathinae), which are specialized to spawn on the gills of certain freshwater mussels, have been declining dramatically during the last few decades. To identify factors affecting the local occurrence of the threatened bitterling species Tanakia lanceolata, we measured its presence and absence, along with several environmental factors, at 68 sites within agricultural canal networks in the Lake Mikata basin, Fukui Prefecture, Japan. Based on the theoretical information approach of Akaike's information criterion, generalized linear mixed models were constructed. These revealed that the species' occurrence is strongly affected by five major factors: the presence of freshwater mussels Anodonta sp., water depth, floating plants coverage, the presence of bullfrogs, and submerged plants coverage. The probability of the presence of T. lanceolata was higher at shallower sites with lower floating plants coverage, located within channels containing mussel beds. These results suggest that mussel-containing channel systems are high-priority conservation zones for T. lanceolata. [ABSTRACT FROM AUTHOR]

A new species of bitterling, Acheilognathus striatus sp. nov., is described on the basis of 57 specimens collected from the lower Yangtze River in Jiangxi Province, China. It can be distinguished from all congeners by the following combined characters: a pair of relatively long barbels, slightly longer than half of eye diameter; dorsal fin with three simple and 8–9 branched fin rays, anal fin with three simple and 7–8 branched fin rays; a black longitudinal stripe on body from the base of caudal peduncle, distinctly reaching anteriorly to the vertical line from the origin of dorsal fin, broader in males than in females; a scale distance between the longitudinal stripe and lateral line below the origin of dorsal fin; dorsal and anal fin margined with black band in males. [ABSTRACT FROM AUTHOR]

Resource availability may affect both individual fitness and population demography and the effects can interact. We used two experiments to test how breeding resource abundance and its spatial distribution, combined with female abundance, affected male reproductive behavior, population spawning rate, and embryo development and recruitment in the European bitterling ( Rhodeus amarus), a small cyprinid fish that lays its eggs in living unionid mussels. In the first experiment, we found that at the population level the abundance of breeding resources (freshwater mussels) was more important for bitterling recruitment than resource spatial distribution (clumped or regular). In contrast at the individual level, (variability in reproductive success) the spatial distribution of resources was more important, but only when resource abundance was not limiting. Territorial males obtained almost exclusive access to fertilizations when resources were abundant and distributed regularly, but were unable to defend large clusters of resources (when rival abundance was always high) and abandoned territoriality. Surprisingly, territorial males remained aggressive and successfully defended their territories when resources were grouped into a single cluster, but at a low abundance. In the second experiment, more rapid embryo development and larger juvenile body size at the end of the growing season was detected at high resource abundance and low female abundance, indicating that early hatched juveniles survived better and hence investment in offspring production early in the season yields a higher fitness pay-offs. The abundance of females in spawning condition was the best overall predictor of the intensity of male reproductive behavior in both experiments. [ABSTRACT FROM AUTHOR]

Rhodeus pseudosericeusis a native bitterling to the Korean Peninsula and found in very limited areas with small census size. Here, its complete mitochondrial genome was analyzed to provide novel data for the reconstruction of phylogenetic relationship among Acheilognathinae species. The genome was a 16,574 bp long consisting of 1 putative control region, 2 rRNA genes, 22 tRNA and 13 protein-coding genes. The gene arrangement was completely identical to those observed in other Acheilognathinae species as well as in other cyprinid species. In our phylogenetic analyses, three major genera of Acheilognathinae indepedently formed monophyletic groups in the tree reconstructed based on the whole genome sequences, whereasRhodeuswas not recovered as a single monophyly when solely considering protein-coding genes, indicating that the taxonomic reevaluation is still required in this subfamily. [ABSTRACT FROM PUBLISHER]

The article focuses on a study which described the phylogenetic relationships of the Tanakia himantegus complex (Teleostei: Cyprinidae) in Taiwan and China. The study analyzed the complete cytochrome (Cyt) b deoxyribonucleic acid (DNA) sequences of 61 specimens of the Tanakia himantegus complex in order to understand their phylogeny, genetic differentiation and historical demography. A comparison between the characteristics of the Taiwanese himantegus and Chinese chii is also presented. Study authors concluded that bimodal or ragged mismatch distributions for the Chinese chii and Taiwanese himantegus demonstrate that they are either admixtures of two expanding populations or stable populations.

We investigated male assessment of sperm competition in the bitterling, Rhodeus sericeus, a freshwater fish that spawns on the gills of living unionid mussels. Field experiments showed males increased their inspection rate of mussels into which a testis solution containing sperm had been experimentally released. Males avoided leading females to mussels that contained high numbers of embryos, but did not alter their leading behavior in response to the presence of sperm. In laboratory experiments males also increased their inspection rate of mussels into which a testis solution had been released and also failed to alter their leading behavior in response to the presence of sperm in mussels. However, males avoided leading females to mussels in close proximity to other males, and thereby may avoid sperm competition. In a second field study, territorial males were shown to ejaculate into mussels at a low rate in the absence of competitors, increase the frequency of ejaculations in competition with a rival, then decrease relative ejaculate expenditure as the number of competing males increased. Observed data were shown to be significantly correlated with predicted estimates of ejaculate expenditure for a model of sperm competition intensity. We discuss our results in the context of adaptive responses of males to sperm competition. [ABSTRACT FROM AUTHOR]

Sexual selection may operate through either direct selection on preference genes or indirect genetic benefits. However, in many species both direct and indirect selection may operate and can influence female mate and oviposition choice. Adaptations by males for sperm competition can also affect female mate and oviposition choice and can lead to sexual conflict. We investigated the role of direct and indirect benefits and male adaptation to sperm competition for female oviposition decisions in the bitterling, Rhodeus sericeus, a freshwater fish that spawns on the gills of living unionid mussels. Field experiments showed that females chose mussels for spawning on the basis of the number of embryos already in mussels and the body size and/or extent of red coloration of the eyes of territorial males. There was also a significant interaction between these direct and indirect benefits of oviposition choice. Territorial male bitterling avoided leading females to mussels into which rivals had already released sperm. Males also increased their rate of sperm release into mussels in response to sperm release by sneaking males. We discuss the possibility that sexual conflict in oviposition choice occurs in this species. [ABSTRACT FROM AUTHOR]

A new bitterling, Rhodeus pseudosericeus sp. nov., is described on the basis of 31 specimens from five localities included in the Namhan River system, South Korea. The new species is distinguished from other Rhodeus species by the following combination of characters: branched dorsal fin rays 9–10 (mode 9); branched anal fin rays 9–11 (mode 10); longest simple ray of dorsal fin strong and stiff, distally segmented; pelvic fin rays i, 6–7; iris of males blackish; dorsal and anal fins of males grayish in breeding season; karyotype with 2 n = 48 (8m + 20sm + 20st). Rhodeus pseudosericeus sp. nov. is similar to Rhodeus sericeus sericeus in the number of pelvic fin and branched dorsal fin rays and the melanophores present on the dorsal fin membrane, but differs from the latter in having a greater body depth, more branched anal fin rays, fewer vertebrae, a lower number of scales in the lateral series, and differing male nuptial coloration. [ABSTRACT FROM AUTHOR]

Rhodeuscyanorostris Li, Liao & Arai, 2020 is a freshwater fish that is endemic to China and restricted to Chengdu City in Sichuan Province. This study is the first to sequence and characterize the complete mitochondrial genome of R.cyanorostris . The mitogenome of R.cyanorostris is 16580 bp in length, including 13 protein-coding genes, two rRNA genes, 22 tRNA genes, and a control region (D-loop). The base composition of the sequence is 28.5% A, 27.6% C, 26.4% T, and 17.5% G, with a bias toward A+T. The genome structure, nucleotide composition, and codon usage of the mitogenome of R.cyanorostris are consistent with those of other species of Rhodeus . To verify the molecular phylogeny of the genus Rhodeus , we provide new insights to better understand the taxonomic status of R.cyanorostris . The phylogenetic trees present four major clades based on 19 mitogenomic sequences from 16 Rhodeus species. Rhodeuscyanorostris exhibits the closest phylogenetic relationship with R.pseudosericeus , R.amarus , and R.sericeus . This study discloses the complete mitochondrial genome sequence of R.cyanorostris for the first time and provides the most comprehensive phylogenetic reconstruction of the genus Rhodeus based on whole mitochondrial genome sequences. The information obtained in this study will provide new insights for conservation, phylogenetic analysis, and evolutionary biology research., (Wenjing Li, Ning Qiu, Hejun Du.)