The grass carp (Ctenopharyngodon idella) aquaculture industry is severely threatened by GCRV-induced hemorrhagic disease. Breeding GCRV-resistant grass carp is an effective strategy to mitigate these losses, but molecular targets with in vivo functional validation remain scarce. In this study, we identified 7-dehydrocholesterol reductase (Dhcr7), a highly conserved enzyme in cholesterol biosynthesis, as a promising target for GCRV-resistant breeding. Dhcr7 is predominantly expressed in the hepatopancreas and brain of grass carp. To assess its breeding potential, we generated dhcr7 knockout grass carp using CRISPR/Cas9 and selected crispants with > 50% mutation rates. Disruption of dhcr7 gene in mutants was confirmed at both mRNA and metabolite levels. Following GCRV-II challenge, these dhcr7 crispants showed ∼40% higher survival rates than wild-type controls, along with significantly upregulated antiviral immune, reduced viral loads, and markedly attenuated hepatopancreas damage. Mechanistically, Dhcr7 deficiency increased Irf3 protein levels, leading to enhanced activation of antiviral immunity. Importantly, dhcr7 disruption did not impair growth performance or muscle morphology. Collectively, our work uncovers a key antiviral role of grass carp dhcr7 and provides a valuable molecular target and a practical strategy for disease-resistant breeding in grass carp.

THOR (testis-associated highly conserved oncogenic long non-coding RNA) is a highly conserved and testis-enriched lncRNA across vertebrates that plays diverse roles in various cancers. However, its physiological function and regulatory mechanism in testes remain largely unknown. Here, we investigated the genomic location and expression pattern of THOR in the model organism zebrafish, and generated a homozygous THOR knockout model using CRISPR-Cas9 technology. Loss of THOR in zebrafish impaired spermatogenesis, leading to oligospermia (38.7% reduction in sperm count), reduced sperm motility, sperm ultrastructural defects, and decreased fertilization rates. RNA-seq analysis of WT and THOR knockout testes revealed dysregulation of cell cycle-related genes, including cdkn1d, foxo1a, tsc1a, tsc2, atrx, and rad21b. RNA pulldown assays in zebrafish testes identified 486 potential THOR-interacting proteins primarily involved in ribosome biogenesis, RNA splicing, chromatin architecture, and meiotic progression. Notably, the core synaptonemal complex components Sycp1, Sycp2, and Sycp3 were all captured as THOR-binding partners. We further demonstrated that THOR directly interacts with Sycp3 and positively regulates its protein levels. Immunostaining assays on chromosome spreads revealed a significantly higher frequency of discontinuous Sycp3 signals in THOR-/- testes, suggesting the presence of meiosis defects caused by Sycp3 downregulation. Our findings expand the understanding of lncRNA-mediated control of spermatogenesis and male infertility by providing the first evidence that lncRNA THOR interacts with the synaptonemal complex to regulate meiosis progression.

The Chinese mitten crab (Eriocheir sinensis), a key species in China’s freshwater aquaculture, faces growing threats from Hepatopancreatic Necrosis Syndrome caused by the microsporidian parasite Hepatospora eriocheir. Deciphering the molecular mechanisms underlying host-pathogen interactions is essential for developing effective disease control strategies. While alternative splicing (AS) and alternative polyadenylation (APA) represent a critical regulatory mechanism in immune responses to pathogenic challenges, their functional significance in E. sinensis remains poorly characterized. This study employed RNA-seq to analyze hepatopancreas transcriptomes during H. eriocheir infection, systematically investigating differentially expressed genes (DEGs), AS and APA events dynamics. We identified 831 DEGs (|log2FoldChange| ≥ 1 and p-value < 0.05) enriched in immune-related pathways including G protein-coupled receptor signaling and epithelial morphogenesis. Additionally, 83 AS events and 914 APA events were detected, demonstrating their coordinated regulatory roles in infection responses. Our analysis revealed APA as a novel post-transcriptional modulator of host immunity, providing critical insights into molecular defense mechanisms against microsporidian invasion. These findings advance understanding of RNA processing regulation in invertebrate innate immunity and establish a framework for targeted disease management in crustacean aquaculture.

Microbial communities are increasingly recognized for their essential roles in the reproductive system. However, the microbial communities in healthy gonads—neither in the ovary nor the testis—have not been extensively explored, particularly with respect to sex differentiation. Sex reversal is a unique mode of sex differentiation that is a well-documented phenomenon in various animal species, with the swamp eel (Monopterus albus) being a notable example of a hermaphroditic species that undergoes natural female-to-male sex reversal. Thus, swamp eel offers a robust system for exploring gonad microbial communities and their biological and functional significance. Our study revealed a living microbial community in the gonads of healthy swamp eel, with microbial loads comparable to those found in three distinct niches: gut, skin, and blood. The gonad microbial communities shared > 55 1. Gonadal microbial communities at homeostasis are partially derived from the gut and blood microbiomes. 2. The dominant ovarian bacteria Bacillus leads to ovarian dysbiosis. 3. Prostaglandin E3 may serve as a metabolic biomarker in response to Bacillus. 4. Bacillus induces testicular inflammation and reduces sperm motility in hermaphroditic swamp eel.

MicroRNAs are important post-transcriptional regulators, yet the molecular crosstalk between miRNAs and their target genes during sex differentiation remains poorly understood. Medaka (Oryzias latipes), the first fish in which the sex determination gene was identified, serves as an ideal model for studying this process. Here, we generated gonadal RNA-seq and small RNA-seq data from XYDMY- females, wild-type females and males to explore this crosstalk. A total of twenty-seven RNA-seq datasets, comprising 188 Gb of raw reads, and twenty-seven small RNA-seq datasets, totaling 18 Gb of raw reads, were collected, covering 10, 30 and 120 days. After optimizing the mapping and normalizing, we conducted transcriptional and post-transcriptional dynamic analyses of differentially expressed genes and miRNAs between WT females and males, as well as between WT females and XYDMY- females. Additionally, we integrated the RNA-seq and small RNA-seq data to construct comprehensive interaction networks and performed a detailed analysis of the temporal dynamics in gene and miRNA expression. These resources offer valuable insights into the transcriptional regulation of gonadal differentiation and development in vertebrates.

The swamp eel (Monopterus albus) is an economically important freshwater fish. However, its natural sex reversal contributes to low egg production and fry shortages in aquaculture. The molecular mechanisms governing this process remain poorly understood, hindered by incomplete gene annotations and a lack of comprehensive multi-omics characterization of the gonad. To address this, we performed integrated Iso-seq, RNA-seq, and ATAC-seq profiling across nine key stages of natural female-to-male sex reversal. This approach revealed an extensive, previously unannotated transcriptome landscape, identifying 37,911 novel transcripts. These included 16,900 novel genes and alternative isoforms derived from 24,193 annotated genes. Furthermore, chromatin accessibility mapping identified 2,174 putative cis-regulatory elements, uncovering dynamic regulatory shifts correlated with gene expression changes during sex reversal. Our integrated multi-omics analysis delivers a significantly enhanced transcript annotation framework for M. albus, resolving precise polyadenylation sites and surpassing the current NCBI annotation in comprehensiveness. Collectively, this work establishes an essential resource for investigating gonadal development and deciphering sex reversal mechanisms in fish.

The greater amberjack is a very important fishery species with high commercial value, and it is distributed worldwide. Transcriptome-based studies on S. dumerili have been limited by an inadequate reference genome and a lack of well-annotated full-length transcripts. In this study, a total of 12 tissues from juvenile and adult fish both sexes were collected for next-generation RNA sequencing (RNA-seq) and full-length isoform sequencing (Iso-seq). For Iso-seq, a total of 163,218, 149,716, and 189,169 high-quality unique transcript sequences were obtained, with an N50 of 5,441, 5,255, and 5,939, from juvenile, adult male and adult female S. dumerili, respectively. We integrated the Iso-seq and RNA-seq data to construct a comprehensive gene annotation and systematically profiled the dynamics of gene expression across the 12 tissues. Our gene models had greater detail and accuracy than those from NCBI and Ensembl, with more precise polyA locations. These resources serve as a foundation for functional genomic studies and provide valuable insights into the molecular mechanisms underlying the development, reproduction and commercial traits of amberjack.

INTRODUCTION:Global warming is increasing interest in how aquatic animals can adjust their physiological performance and cope with temperature changes. Therefore, understanding the behavioral changes and molecular underpinnings in fish under warming is crucial for both the individual and groups survival. This could provide experimental evidence and resource for evaluating the impact of global warming. OBJECTIVE:Three genetic families of common carp (Cyprinus carpio) were generated. These juveniles were constructed short-term (4 days) and long-term (30 days) warming groups to investigate the effects of warming on behavioral responses and to elucidate the potential underlying mechanisms of warming-driven behavior. METHODS:Behavioral tests were used to explore the effects of short- and long-term exposure to warming on the swimming behavior of C. carpio. Brain transcriptome combined with measurement of nervous system activity was used to further investigated the comprehensive neuromolecular mechanisms under warming. RESULTS:Long-term warming groups had a more significant impact on the decline of swimming behavior in juvenile C. carpio. Furthermore, brain comparative transcriptomic analysis combined with measurement of nervous system activity revealed that genes involved in cytoskeletal organization, mitochondrial regulation, and energy metabolism are major regulators of behavior in the juvenile under warming. Importantly, especially in the long-term warming groups, enrichment analysis of associated gene expression suggested functional alterations of synaptic transmission and signal transduction leading to swimming function impairment in the central nervous system, as revealed by behavioral tests. CONCLUSIONS:Our study provides evidence of the neurogenomic mechanism underlying the decreased swimming activity in juvenile C. carpio under warming. These findings have important implications for understanding the impacts of climate change on aquatic ecosystems and the organisms that inhabit them.

The swamp eel (Monopterus albus) is a commonly cultured freshwater fish. Selection and cultivation of fecund broodstock is crucial for efficient artificial reproduction in this species. However, there are currently no guidelines for selecting high-quality males in M. albus. This study quantitatively investigated the sperm motility of male swamp eels during the breeding season by using computer-assisted sperm analysis system. Variability in the proportion and number of motile sperm was observed between individual males. The testes were grouped into high-quality and low-quality according to sperm quality. Morphometric parameters of the two groups were analyzed. We found that high-quality testes were longer (150 +/- 27 mm verses 127 +/- 19 mm) than low-quality testes. Besides, the proportion of testes with a dark appearance was slightly higher (58.3% verses 48.1%) in the high-quality group than in the low-quality group. Metabolomic analysis was conducted to compare the metabolite profiles of high-quality and low-quality testes. Glycerophospholipids, organic acids, glycerolipids, amino acids, sphingolipids, and nucleotides were the most abundant metabolites in the testes of swamp eels. Moreover, 135 differential metabolites were identified. Several nucleotide derivatives, including 5'-deoxy-adenosine, 2'-deoxyadenosine, and ribosyl adenosine, were the most significantly enriched metabolites in high-quality testes. These metabolites are potential indicators for the testis quality in M. albus. Altogether, our work provides systematic and quantitative data about the physiological and biochemical characteristics of M. albus testis, which provides an evidential basis for the selection of high-fecundity parents to improve artificial repro-duction efficiency of M. albus.

Various bacterial diseases have caused great economic losses to the high-density and intensive aquaculture industry; however, the pathogenic mechanism underlying the large-scale challenged to caused by many bacteria remain unclear, making the prevention and treatment of these diseases difficult. In the present study, we isolated a bacterial strain from Cyprinus carpio having a typical bacterial disease and named it Cc2021. Through subsequent morphological observations, a regression challenge, biochemical identification, and 16S rRNA gene sequence analysis, we determined Cc2021 to be Plesiomonas shigelloides . Subsequently, we comprehensively investigated the pathogenicity of P. shigelloides in C. carpio through a regression challenge and assessed the underlying the pathogenic mechanism. Mortality results revealed that P. shigelloides is highly pathogenic and infects various tissues throughout the body, resulting in edema of the liver, spleen, and body and head kidneys. Histopathological analysis revealed obvious inflammation, bleeding, and necrosis in the intestine, spleen, and head kidney. The body’s immune tissues actively produce complement C3, superoxide dismutase, and lysozyme after a challenge to resist bacterial invasion. With regard to the underlying pathogenesis of P. shigelloides , comparative transcriptome analysis revealed 876 upregulated genes and 828 downregulated genes in the intestine of C. carpio after the challenge. Analysis of differentially expressed unigenes revealed the involvement of major immune pathways, particularly the TNF signaling pathway, interleukin (IL)-17 signaling pathway, and Toll-like receptor signaling pathway. The present study provides new valuable information on the immune system and defense mechanisms of P. shigelloides .

Alternative splicing is an important way of regulating gene functions in eukaryotes. Several key genes involved in sex determination and gonadal differentiation, such as nr5a1 and ddx4, have sex-biased transcripts between males and females, suggesting a potential regulatory role of alternative splicing in gonads. Currently, the sex-specific alternative splicing events and genes have not been comprehensively studied at the genome-wide level in zebrafish. In this study, through global splicing analysis on three independent sets of RNA-seq data from matched zebrafish testes and ovaries, we identified 120 differentially spliced genes shared by the three datasets, most of which haven’t been reported before. Functional enrichment analysis showed that the GO terms of mRNA processing, mRNA metabolism and microtubule-based process were strongly enriched. The testis- and ovary-biased alternative splicing genes were identified, and part of them (tp53bp1, tpx2, mapre1a, kif2c, and ncoa5) were further validated by RT-PCR. Sequence characteristics analysis suggested that the lengths, GC contents, and splice site strengths of the alternative exons or introns may have different influences in different types of alternative splicing events. Interestingly, we identified an unexpected high proportion (over 70%) of non-frameshift exon-skipping events, suggesting that in these cases the two protein isoforms derived from alternative splicing may both have functions. Furthermore, as a representative example, we found that the alternative splicing of ncoa5 causes the loss of a conserved RRM domain in the short transcript predominantly produced in testes. Our study discovers novel sex-specific alternative splicing events and genes with high reliabilities in zebrafish testes and ovaries, which would provide attractive targets for follow-up studies to reveal the biological significances of alternative splicing events and genes in sex determination and gonadal differentiation.

The common carp (Cyprinus carpio) accounts for approximately 10% of the annual freshwater aquaculture production and is an ideal model to study cyprinidae reproduction. Female common carp grow faster than the males; therefore, related research presents an opportunity with high application value. Although we have a detailed understanding of common carp's early gonadal differentiation process, information about genome-wide gene expression, regulation, and underlying molecular mechanisms during this process remain limited. Here, time-course data comprising six key stages during testicular differentiation and maturation were investigated to further understand the molecular mechanisms underlying the testicular development in cyprinid species. After integrating these time-series data sets, common carp genome, including 98,345 novel transcripts and 3,071 novel genes were re-annotated and precisely updated. Gene co-expression network analysis revealed that the ubiquitin-mediated proteolysis pathway was essential for metabolism during testicular differentiation in the endocrine system of C. carpio. Functional enrichment analyses indicated that genes mainly related to amino acid metabolism and steroid hormone synthesis were relatively highly expressed at the testicular undifferentiation stages, whereas genes associated with cell cycle and meiosis were expressed from the beginning of testicular differentiation until maturation. The dynamics of alternative splicing events demonstrated that exon skipping accounted for majority of the alternative splicing events in the testis and the brain during gonad development. Notably, several potential male-specific genes (fanci and sox30) and brain-specific genes (oxt, gad2, and tac1, etc.) were identified. Importantly, we traversed beyond the level of transcription to test for stage- and gonad-specific alternative splicing patterns between the brain and testis. This study is the first to describe a comprehensive landscape of alternative splicing events and gene expression patterns during gonadogenesis in common carp. This work is extremely valuable to elucidate the mechanisms underlying gonadal differentiation in Cyprinidae as well as other fish species.

研究报道了中国首例摇蚊微孢子虫,结合各发育阶段形态特征、生态学特征及分子特征,鉴定其为萨梅诺娃新佩雷斯虫Neoperezia semenovaiae Issi,et al.2012,系我国新记录.萨梅诺娃新佩雷斯虫寄生于羽摇蚊幼虫脂肪体组织,导致其体表呈白浊状.成熟孢子呈卵圆形,孢子长(5.7±0.2)μm(5.3—6.3μm),宽(3.7±0.1)μm(3.4—4.0μm).透射电镜观察显示各发育阶段均为离核,发育不同步,与宿主细胞质直接接触.早期发育阶段为高电子密度的多核裂殖体阶段,经原生质团分裂形成单核或多核产孢体,进一步发育为单核孢子母细胞.孢子母细胞形状不规则,周围被内质网环绕,并逐渐形成微孢子虫的典型结构如极丝、极质体和三层孢壁等.成熟孢子卵圆形,离核,细胞核较大,位于孢子正中央,被大量核糖体包围.极质体分为两部分,前半部分为海绵状,后半部分薄膜状.锚状盘位于孢子前端,呈蘑菇状.孢壁三层,外层为高电子密度层,厚26.5—62.7 nm,中间层为电子透明层,厚151.8—236.1 nm,里层为质膜层.同型极丝,30—31圈,分2—3列排列.扩增获得其小核糖体序列为1356 bp,序列比较发现其与俄罗斯列宁格勒区羽摇蚊的N.semenovaiae相似性为99.1％.系统发育关系分析表明N.semonovaiae与Neoperezia、Bryonosema、Schroedera属种类聚为一独立进化枝,N.semonovaiae种群出现明显的地理分化.

Liver myxobolosis, caused by Myxobolus wulii severely prevents the sustainable development of gibel carp (Carassius auratus gibelio) aquaculture in China. More insights into the host-parasite interaction will undoubtedly help to develop potential solutions to control this myxobolosis. Liver is an important organ to perform immunological and metabolic functions, changes of gene expression profile involved in fish liver against the local myxosporean infection, however, remain unknown. Here, a comparative transcriptomic analysis of severely infected and mildly infected liver from the same fish individuals, liquefying liver from the just died fish and control liver from the uninfected fish was conducted to investigate the possible involved molecular responses in the liver against the M. wulii infection. Upregulated differentially expressed genes (DEGs) were predominantly involved in adaptive immune responses, including the anti-inflammatory responses resulted from the synergism of Th1, Th17 and Treg cells, and antibody responses mediated by B cells. Downregulated DEGs were mainly involved in metabolic processes. Furthermore, 10 representative DEGs possibly involving in the immunemetabolic interactions were downregulated in the affected liver, demonstrating that the possible synergic mechanism of the suppression of metabolic activities and the facilitation of anti-inflammatory responses occurred in the infected liver. Combining the significant downregulation of cytoskeleton-related genes and upregulation of cell size-related genes, the histopathological, transmission and scanning electron microscopic analysis, it can be suspected that M. wulii is of intracellular infection. This is the first study to elucidate the molecular mechanism of immune-metabolic interactions underlying the fish liver myxobolosis, which will deepen the knowledge of the fish-myxospoean dialogue.

Zn 2+ is required for the activity of many mitochondrial proteins, which regulate mitochondrial dynamics, apoptosis and mitophagy. However, it is not understood how the proper mitochondrial Zn 2+ level is achieved to maintain mitochondrial homeostasis. Using Caenorhabditis elegans , we reveal here that a pair of mitochondrion-localized transporters controls the mitochondrial level of Zn 2+ . We demonstrate that SLC-30A9/ZnT9 is a mitochondrial Zn 2+ exporter. Loss of SLC-30A9 leads to mitochondrial Zn 2+ accumulation, which damages mitochondria, impairs animal development and shortens the life span. We further identify SLC-25A25/SCaMC-2 as an important regulator of mitochondrial Zn 2+ import. Loss of SLC-25A25 suppresses the abnormal mitochondrial Zn 2+ accumulation and defective mitochondrial structure and functions caused by loss of SLC-30A9. Moreover, we reveal that the endoplasmic reticulum contains the Zn 2+ pool from which mitochondrial Zn 2+ is imported. These findings establish the molecular basis for controlling the correct mitochondrial Zn 2+ levels for normal mitochondrial structure and functions.

为有效鉴定三棱碘泡虫的有效性,补充其生物学特征,实验利用现代粘孢子虫整合分类学方法,包括形态特征、寄生特性(宿主特征和寄生部位)及分子特征,对其进行重新描述,证实其分类有效性,探讨其系统发育关系.结果显示,三棱碘泡虫专性寄生于草鱼鳃丝间,未在其他器官(肝脏、肾脏、肠道等)检获孢子.包囊呈乳白色,长椭圆形,长(2.4±0.3)(2.1～2.7)mm,宽(0.8±0.1)(0.6～0.9)mm.成熟孢子壳面观呈卵圆形,孢子后端未见"V"形褶皱,孢子外包裹有一层透明的圆形黏液膜,缝面观呈纺锤形,孢子缝面可见三条平行而突出的脊线;孢质均匀,孢子后端具有一个大嗜碘泡;成熟孢子长(10.3±0.4)(9.4～11.0)μm,宽(9.5±0.5)(8.7～10.9)μm,厚(7.4±0.5)(6.4～8.0)μm;两极囊等大,梨形,极丝7～8圈;组织病理显示,病灶鳃组织未出现严重炎症反应.BLAST比对发现,三棱碘泡虫与隐杆碘泡虫小核糖体RNA序列相似性最高(89.58％),但远低于种内序列相似性.分子系统发育分析结果显示,三棱碘泡虫先与寄生于鲤科鱼类的隐杆碘泡虫形成姊妹关系,再与寄生于胭脂鱼科鱼类鳃的诺布尔碘泡虫、微小碘泡虫及毕斯塔斯碘泡虫形成独立的鳃寄生碘泡虫分枝,表明宿主亲缘关系与组织趋向性在鱼类组织寄生碘泡科粘孢子虫系统演化历程中扮演重要作用.本研究补充了三棱碘泡虫包囊形态结构、组织趋向性及分子数据,证实了其分类有效性.

Arginine catabolism involves enzyme-dependent reactions in both mitochondria and the cytosol, defects in which may lead to hyperargininemia, a devastating developmental disorder. It is largely unknown if defective arginine catabolism has any effects on mitochondria. Here we report that normal arginine catabolism is essential for mitochondrial homeostasis in Caenorhabditis elegans. Mutations of the arginase gene argn-1 lead to abnormal mitochondrial enlargement and reduced adenosine triphosphate (ATP) production in C. elegans hypodermal cells. ARGN-1 localizes to mitochondria and its loss causes arginine accumulation, which disrupts mitochondrial dynamics. Heterologous expression of human ARG1 or ARG2 rescued the mitochondrial defects of argn-1 mutants. Importantly, genetic inactivation of the mitochondrial basic amino acid transporter SLC-25A29 or the mitochondrial glutamate transporter SLC-25A18.1 fully suppressed the mitochondrial defects caused by argn-1 mutations. These findings suggest that mitochondrial damage probably contributes to the pathogenesis of hyperargininemia and provide clues for developing therapeutic treatments for hyperargininemia.

A new microsporidian species was described from the hypoderm of Daphnia magna sampled from gibel carp (Carassius auratus gibelio) ponds located in Wuhan city, China. The infected cladocerans generally appeared opaque due to numerous plasmodia distributed in the host integument. The earliest stages observed were uninucleate meronts that were in direct contact with the host cell cytoplasm. Meronts developed into multinucleate sporogonial plasmodia enclosed in sporophorous vesicles. Sporoblasts were produced by the rosette-like division of sporogonial division. Mature spores were pyriform and monokaryotic, measuring 4.48 ± 0.09 (4.34-4.65) µm long and 2.40 ± 0.08 (2.18-2.54) µm wide. The polaroplast was bipartite with loose anterior lamellae and tight posterior lamellae. Polar filaments, arranged in two rows, were anisofilar with two wider anterior coils, and five narrower posterior coils. The exospore was covered with fibrous secretions and was composed of four layers. Phylogenetic analysis based on the obtained SSU rDNA sequence, indicated that the present species clustered with three unidentified Daphnia pulicaria-infecting microsporidia with high support values to form a monophyletic lineage, rather than with the congener, Agglomerata cladocera. The barcode motif of the internal transcribed spacer (ITS) region of the novel species was unique among representatives of the "Agglomeratidae" sensu clade (Vávra et al., 2018). Based on the morphological characters and SSU rDNA-inferred phylogenetic analyses, a new species was erected and named as Agglomerata daphniae n. sp. This is the first report of zooplankton-infecting microsporidia in China.

We report a new microsporidium Jirovecia sinensis sp. n. from a freshwater oligochaete, Branchiura sowerbyi collected in Hongze city, Jiangsu province, East China. Numerous whitish hypertrophied coelomocytes of 0.33-0.59 mm in diameter indicated infection. Transmission electron microscopy observations revealed that all developmental stages were diplokaryotic. The earliest life stages observed were meronts that were in direct contact with host cytoplasm, accumulated peripherally in the hypertrophied coelomocytes and connected with host cytoplasm through many pinocytotic canals. Mature spores are rod-shaped with a blunt end, measuring 17.0 +/- 0.1 (14.9-18.5) mu m long and 2.0 +/- 0.2 (1.7-2.2) mu m wide. The most conspicuous character of the novel microsporidian parasite is the tail-like posterior prolongations, with a length of 29.6-40.8 mu m. Mature spores have a manubrium with a diameter of 447-485 nm which consist of six density-discontinuous concentric circles. Spores possess a collar-shaped anchoring disk and a bipartite polarplast with an anterior lamellar region and a posterior tubular section. SSU rDNA-based phylogenetic analysis indicated with high support values that the new species clustered with two Bacillidium species (B. vesiculoformis and Bacillidium sp.) infecting the freshwater oligochaetes and Janacekia debaisieuxi infecting the insect Simulium maculatum. Based on the ultrastructural features and molecular characteristics, a new species in the genus Jirovecia, Jirovecia sinensis sp. n., is designated.