Myxobolus acanthogobii Hoshina, 1952 and Myxobolus selari n. sp. (Myxosporea: Myxobolidae) infecting brain of commercial fishes in Terengganu, Malaysia.

Myxosporean infection in marine water fishes has drawn less attention than in freshwater fishes, which resulted in a higher taxonomic variety in freshwater in Malaysia. This study aimed to address the gap by conducting a myxosporean survey on two commercially significant marine fish species, Nemipterus furcosus (Valenciennes) (Eupercaria incertae sedis: Nemipteridae) and Selar crumenophthalmus (Bloch) (Carangiformes: Carangidae), collected from the northeastern part of peninsular Malaysia. During the examination of the organs, two distinct Myxobolus Bütschli, 1882 species were discovered in the brain tissue of these fishes, despite the absence of any observable pathological signs. The two Myxobolus species were characterized through morphometry, morphology, and analysis of partial small subunit ribosomal RNA (18S rDNA) gene. As a result, Myxobolus acanthogobii Hoshina, 1952, which infects 2.3% of N. furcosus, is synonymous with a myxobolid species commonly found in Japanese waters, based on its morphological traits, tissue tropism, and molecular diagnostics. Furthermore, a novel species, Myxobolus selari n. sp., was described, infecting the brain of one (11%) individual S. crumenophthalmus. This unique species displayed distinctive features, placing it within a well-supported subclade primarily comprising brain-infecting myxobolids. Maximum likelihood analysis further revealed the close relationships among these brain-infecting myxobolids, underscoring the significance of tissue tropism and host taxonomy for myxobolids. This study represents the initial documentation of Myxobolus species within the southern South China Sea, shedding light on the potential diversity of marine myxosporean in this region. This article was registered in the Official Register of Zoological Nomenclature (ZooBank) as urn:lsid:zoobank.org:pub:7C400E35-7CB8-4DEE-92B7-F75FF3926441.

First report of Myxobolus neurofontinalis (Bivalvulida: Myxobolidae) infecting anadromous Brook Trout from Prince Edward Island, Canada.

OBJECTIVE: During routine histological examination of tissues from mortality events of anadromous Brook Trout Salvelinus fontinalis from Prince Edward Island (PEI), Canada, myxospores consistent with Myxobolus were observed infecting the central nervous system. The objective of this study was to identify the species of Myxobolus infecting the nervous system of anadromous Brook Trout from PEI, Canada. METHODS: Myxospore morphology, small subunit (SSU) ribosomal DNA (rDNA) sequence data, and histology were used to identify myxospores isolated from infected Brook Trout. RESULT: Myxospore measurements from the PEI samples matched those reported in the description of Myxobolus neurofontinalis from North Carolina. A 1057-bp fragment of the SSU rDNA from myxospores collected from Brook Trout in PEI was identical to an isolate of M. neurofontinalis (MN191598) collected previously from the type locality, New River basin, North Carolina. Histological sections confirmed infections were intercellular in the central nervous system. Minimal host response was observed, with only sparse mononuclear inflammatory infiltrates present at the periphery of and within dispersed myxospores, suggesting that infections are not pathogenic to Brook Trout. CONCLUSION: Myxospores were identified as M. neurofontinalis, which was previously described from the central nervous system of Brook Trout from the New River basin, North Carolina, USA. This constitutes the first time M. neurofontinalis has been documented outside of the New River basin in North Carolina.

The Immune Response to the Myxozoan Parasite Myxobolus cerebralis in Salmonids: A Review on Whirling Disease.

Salmonids are affected by the economically significant whirling disease (WD) caused by the myxozoan parasite Myxobolus cerebralis. In the past, it was endemic to Eurasia, but it has now spread to different regions of North America, Europe, New Zealand, and South Africa. Among salmonids, rainbow trout is considered the most highly susceptible host. Upon entering to the host's body, the parasite invades the spine and cranium, resulting in whirling behaviour, a blackened tail, and destruction of cartilage. The disease is characterized by the infiltration of numerous inflammatory cells, primarily lymphocytes and macrophages, with the onset of fibrous tissue infiltration. Several efforts have been undertaken to investigate the role of various immune modulatory molecules and immune regulatory genes using advanced molecular methods including flow cytometry and transcriptional techniques. Investigation of the molecular and cellular responses, the role of STAT3 in Th17 cell differentiation, and the inhibitory actions of suppressors of cytokine signaling (SOCS) on interferons and interleukins, as well as the role of natural resistance-associated macrophage proteins (Nramp) in WD have significantly contributed to our understanding of the immune regulation mechanism in salmonids against M. cerebralis. This review thoroughly highlights previous research and discusses potential future directions for understanding the molecular immune response of salmonids and the possible development of prophylactic approaches against WD.

Myxobolus xiushanensis n. sp. (Myxozoa: Myxobolidae) infecting the gill arches of Yellowhead Catfish Tachysurus fulvidraco from China.

OBJECTIVE: Myxosporidiosis of bagrid fishes has been a focus of aquaculture research in recent years. The purpose of this study is to characterize a novel myxobolid, named Myxobolus xiushanensis n. sp., infecting Yellowhead Catfish Tachysurus fulvidraco in China. METHODS: We used molecular biology, morphology, phylogeny, and histopathology in the present study. RESULT: Mature myxospores were circular to ellipsoidal in valve view, measuring 12.2 ± 0.4 µm (mean ± SD; range = 11.2-13.2 µm) in length and 10.6 ± 0.4 µm (9.5-11.1 µm) in width. Two oval polar capsules were equal in width (3.4 ± 0.2 µm; 3.0-3.8 µm) but slightly unequal in length: 5.6 ± 0.3 µm (5.3-6.1 µm) and 4.7 ± 0.2 µm (4.4-5.5 µm). The polar capsule was packed with five to seven spirals of polar tubules. Histopathological investigation demonstrated that the plasmodium under the cuticular layer of the gill arch only induced a local inflammatory response and did not cause serious damage to the gill arch's internal structure. The two small subunit (SSU) ribosomal DNA sequences of M. xiushanensis n. sp. showed 100% similarity and uniqueness, and the highest similarity with other myxosporean sequences in GenBank was 90.27% (query coverage = 94%). The secondary structures of the SSU ribosomal RNA revealed that the present species was distinctly different from related species in regions V4 and V7. Phylogenetic analysis showed that M. xiushanensis n. sp. clustered independently within a branch. CONCLUSION: These results enrich our understanding of the biodiversity of myxobolids infecting bagrid fishes and provide fundamental data for the diagnosis of myxosporidiosis.

The first detection of Myxobolus lentisuturalis Dyková, Fiala et Nie, 2002, a highly pathogenic muscle-infecting parasite of gibel carp (Carassius auratus gibelio Berg, 1932) in Hungary.

Myxobolus lentisuturalis is a myxosporean parasite infecting the musculature both of goldfish (Carassius auratus auratus) and gibel carp (Carassius auratus gibelio). The species was originally described in China from gibel carp that is a common fish for sport fishing in Hungary meanwhile is one of the most popular farmed fish in China due to its high demand. Eighteen gibel carp with distortions were collected from a barrage pond in southern Hungary. All fish had large humps in the dorsolateral region due to infection of the muscle between the head and the dorsal fin. The swollen degenerated tissue was filled with myxozoan spores, which were collected for morphological and molecular studies. By size and morphology, the spores were consistent with morphological description of M. lentisuturalis. Histopathological examination showed that the formation of plasmodia containing myxospores leads to severe destruction of muscle tissue. The 18S ribosomal DNA and 28S ribosomal DNA data of the samples presented matched with previous sequences of M. lentisuturalis in GenBank. Phylogenetic analyses confirmed that our sequences belong to a monophyletic group with them supported by a high bootstrap. This study highlights the occurrence of a highly pathogenic myxozoan, M. lentisuturalis in Hungary as a new geographical location.

The Molecular Mechanisms Employed by the Parasite Myxobolus bejeranoi (Cnidaria: Myxozoa) from Invasion through Sporulation for Successful Proliferation in Its Fish Host.

Myxozoa is a unique group of obligate endoparasites in the phylum Cnidaria that can cause emerging diseases in wild and cultured fish populations. Recently, we identified a new myxozoan species, Myxobolus bejeranoi, which infects the gills of cultured tilapia while suppressing host immunity. To uncover the molecular mechanisms underlying this successful parasitic strategy, we conducted transcriptomics analysis of M. bejeranoi throughout the infection. Our results show that histones, which are essential for accelerated cell division, are highly expressed even one day after invasion. As the infection progressed, conserved parasitic genes that are known to modulate the host immune reaction in different parasitic taxa were upregulated. These genes included energy-related glycolytic enzymes, as well as calreticulin, proteases, and miRNA biogenesis proteins. Interestingly, myxozoan calreticulin formed a distinct phylogenetic clade apart from other cnidarians, suggesting a possible function in parasite pathogenesis. Sporogenesis was in its final stages 20 days post-exposure, as spore-specific markers were highly expressed. Lastly, we provide the first catalog of transcription factors in a Myxozoa species, which is minimized compared to free-living cnidarians and is dominated by homeodomain types. Overall, these molecular insights into myxozoan infection support the concept that parasitic strategies are a result of convergent evolution.

Myxozoan survey of thicklip grey mullet Chelon labrosus reinforces successful radiation of Myxobolus in mugiliform hosts.

A myxozoan survey was performed on specimens of thicklip grey mullet Chelon labrosus (Risso) captured from the Douro River estuary, northern Portugal. Eleven new species, all belonging to the genus Myxobolus Bütschli, 1882 (M. abdominalis n. sp., M. aestuarium n. sp., M. caudalis n. sp., M. chelonari n. sp., M. cucurbitiformis n. sp., M. douroensis n. sp., M. intestinicola n. sp., M. invictus n. sp., M. labicola n. sp., M. peritonaei n. sp., and M. pinnula n. sp.) are described based on microscopic and molecular data, confirming the known high radiation of these myxozoans in mullets. Additionally, Myxobolus pupkoi Gupta et al., 2022 is reported for the first time from C. labrosus, bringing forth a novel case of morphological plasticity between geographic isolates. We consider that molecular-based comparisons are imperative for the description of mugiliform-infecting Myxobolus, with distance estimation further matching two of the novel Myxobolus spp. with sphaeractinomyxon types previously reported from another Portuguese estuary. This finding supports sphaeractinomyxon as specific life cycle counterparts of Myxobolus that infect mullets. Phylogenetic analyses of 18S rDNA retrieved a monophyletic clade of mugiliform-infecting myxobolids comprising well-supported lineages of species parasitizing mullets from the genera Chelon, Mugil, Crenimugil, and Planiliza. The existence of more than one Chelon- and Planiliza-infecting lineage reveals that myxobolids parasitized members of these genera multiple times during their evolution. Lastly, the elevated number of unmatched sphaeractinomyxon sequences included in the Chelon-infecting lineages clearly shows that Myxobolus diversity hosted by this genus remains underrated.

Title: Un inventaire des myxozoaires du mulet lippu Chelon labrosus confirme le rayonnement réussi de Myxobolus chez les hôtes mugiliformes. Abstract: Un inventaire des myxozoaires a été réalisé sur des spécimens de mulets lippus Chelon labrosus (Risso) capturés dans l'estuaire du fleuve Douro, au nord du Portugal. Onze nouvelles espèces, toutes appartenant au genre Myxobolus Bütschli, 1882 (M. abdominalis n. sp., M. aestuarium n. sp., M. caudalis n. sp., M. chelonari n. sp., M. cucurbitiformis n. sp., M. douroensis n. sp., M. intestinicola n. sp., M. invictus n. sp., M. labicola n. sp., M. peritonaei n. sp. et M. pinnula n. sp.) sont décrites sur la base de données microscopiques et moléculaires, confirmant le rayonnement connu de ces myxozoaires chez les mulets. De plus, Myxobolus pupkoi Gupta et al., 2022 est signalé pour la première fois chez C. labrosus, démontrant un nouveau cas de plasticité morphologique entre des isolats géographiques. Nous considérons que les comparaisons moléculaires sont impératives pour la description des Myxobolus infectant les mugiliformes, l'estimation de la distance correspondant en outre à deux des nouveaux Myxobolus spp. avec des types de sphaeractinomyxons précédemment signalés dans un autre estuaire portugais. Cette découverte soutient les sphaeractinomyxons en tant que contreparties spécifiques du cycle de vie de Myxobolus qui infectent les mulets. Les analyses phylogénétiques de l'ADNr 18S ont montré un clade monophylétique de Myxobolidae infectant les mugiliformes, comprenant des lignées robustes d'espèces parasitant les mulets des genres Chelon, Mugil, Crenimugil et Planiliza. L'existence de plusieurs lignées infectant Chelon et Planiliza révèle que les Myxobolidae ont parasité des membres de ces genres plusieurs fois au cours de leur évolution. Enfin, le nombre élevé de séquences de sphaeractinomyxons non appariées incluses dans les lignées infectant Chelon montre clairement que la diversité de Myxobolus hébergée par ce genre reste sous-estimée.

Diversity of myxozoans (Cnidaria) infecting Neotropical fishes in southern Mexico.

Myxozoans are a unique group of microscopic parasites that infect mainly fishes. These extremely reduced cnidarians are highly diverse and globally distributed in freshwater and marine habitats. Myxozoan diversity dimension is unknown in Mexico, a territory of an extraordinary biological diversity. This study aimed to explore, for the first time, myxozoan parasite diversity from fishes of the Neotropical region of Mexico. We performed a large morphological and molecular screening using host tissues of 22 ornamental and food fish species captured from different localities of Veracruz, Oaxaca and Chiapas. Myxozoan infections were detected in 90% of the fish species, 65% of them had 1 or 2 and 35% had 3 and up to 8 myxozoan species. Forty-one putative new species were identified using SSU rDNA phylogenetic analyses, belonging to two main lineages: polychaete-infecting (5 species) and oligochaete-infecting (36 species) myxozoans; from those we describe 4 new species: Myxidium zapotecus sp. n., Zschokkella guelaguetza sp. n., Ellipsomyxa papantla sp. n. and Myxobolus zoqueus sp. n. Myxozoan detection increased up to 6 × using molecular screening, which represents 3.7 × more species detected than by microscopy. This study demonstrated that Neotropical fishes from Mexico are hosts of a multitude of myxozoans, representing a source of emerging diseases with large implications for economic and conservation reasons.

Myxobolus lentisuturalis infection in a farmed population of goldfish Carassius auratus from the USA.

Myxobolus lentisuturalis is a myxozoan parasite of piscine muscle that has been described in goldfish Carassius auratus and Prussian carp Carassius gibelio. This report documents a naturally occurring infection of M. lentisuturalis in a population of farmed goldfish in the USA. Postmortem examination was performed on 4 affected goldfish. Gross findings included large cystic cavities along the dorsal midline filled with caseous exudate. Histopathology revealed myxozoan plasmodia and spores in the epaxial muscles with varying degrees of granulomatous and necrotizing myositis accompanied by lymphohistiocytic meningoencephalitis. Spore morphology and dimensions were consistent with M. lentisuturalis, as observed by light microscopy. PCR and sequence analysis of the small subunit ribosomal DNA of infected muscle samples from 2 goldfish confirmed the parasite to have 99-100% nucleotide identity to M. lentisuturalis sequences recovered from similar cases of this parasite infecting goldfish in China and Italy and Prussian carp in China. This is the first reported case of M. lentisuturalis in the USA and furthers the understanding of the pathogenicity of this under-described parasite.

Identification of Myxobolus distalisensis n. sp. (Cnidaria: Myxozoa) infecting yellow catfish Tachysurus fulvidraco (Richardson), with a supplement description of M. voremkhai (Akhmerov, 1960) Landsberg and Lom, 1991.

With growing scale of intensive fish cultivation, the risk of parasite infection in commercial fish is increased. Precisely identifying and characterizing the parasites that infect the farmed fish is critical to understanding the dynamics of their communities. Here, two species of Myxobolus were identified in farmed yellow catfish Tachysurus fulvidraco (Richardson) in China. Myxobolus distalisensis n. sp. developed plasmodia in the gill filaments, with oval to elliptical myxospores measuring 11.3 ± 0.6 (10.4-12.6) × 8.1 ± 0.3 (7.5-8.6) × 5.5 ± 0.2 (5.2-5.8) µm. Two pyriform polar capsules of equal size were measured 5.3 ± 0.4 (4.5-6.3) × 2.7 ± 0.1 (2.3-3) µm. Myxobolus voremkhai (Akhmerov, 1960) Landsberg and Lom, 1991 developed plasmodia in the gill arch and had a myxospore morphology similar to the conspecific isolates described in previous studies. The consensus sequences of M. distalisensis was remarkably distinct from those deposited in the GenBank, with exception of whereas M. voremkhai showing 99.84% identity. The genetic data on both isolates differed considerably from each other, revealing only 86.96% molecular identity. Histologically, M. distalisensis resided in the filament cartilage, and the aggressive proliferation of the sporogenic stages led to lytic cartilage corrosion. In contrast, plasmodia of M. voremkhai grossly observed at the base of the gill filament were embedded by the connective tissue in the gills arch. Phylogenetically, both isolates were separately placed in different subclades, indicating difference in their evolutionary history. Besides, the taxon under the family Myxobolidae was demonstrated non-monophyletic origins, and parasite radiation largely followed their host affinity.

Phylogeny and ultrastructure of Myxobolus rangeli n. sp. (Myxozoa, Bivalvulida), a histozoic parasite in Siluriformes fish from the Amazon region.

A new species of Myxobolus parasitizing the arterial bulb and cardiac musculature of the freshwater fish Pimelodus ornatus Kner, 1858, from the Arari river in the municipality of Cachoeira do Arari, island of Marajó, Pará, Brazil, was described. In the present study, the observed prevalence of myxozoan parasites in the heart tissue of the hosts was 20% (6/30). The myxozoans observed had mature biconvex spores, slightly rounded, an anterior end with two pyriform polar capsules and a posterior end with very evident sporoplasm, measuring 8 ± 0.2 µmin length. The spore width was 5.8 ± 0.4 µm, with a thickness of 3.4 ± 0.2µm. The length of the polar capsules was 3.6 ± 0.3 µm and the width was 1.2 ± 0.2µm, with 6 to 7 turns of the polar filament. The divergences observed, regarding the morphometric and genetic structure of SSU rDNA, in relation to other Myxobolidae already described in the literature, confirm the description of the new species Myxobolus rangeli n. sp.

On the validity and distribution of Myxobolus curemae Vieira, Agostinho, Negrelli, Silva, Azevedo and Abdallah, 2022 (Myxozoa: Bivalvulida) from a new record on the coast of southeastern Brazil.

Myxobolus spp. are parasites of wide diversity and distribution in fish, both in the natural environment and in freshwater or marine farming systems around the world and are sometimes associated with severe disease in their hosts (Schmahl et al. 1989; Lom and Dyková, 1995; Eiras et al. 2021). The white mullet Mugil curema Valenciennes, 1836 is a pelagic fish of the Mugilidae family widely distributed in the Atlantic Ocean (Froese & Pauly 2022). Recently, Myxobolus curemae Vieira, Agostinho, Negrelli, Silva, Azevedo and Abdallah, 2022 was described from white mullets Mugil curema Valenciennes, 1836 in Brazil (Vieira et al. 2022). In the current work, Myxobolus sp. was identified with the same biological and morphological characteristic features of M. curemae from white mullets from the Jacarepaguá Lagoon Complex in the State of Rio de Janeiro, Brazil, in addition to being 100% identical for a genic region of the nuclear small subunit ribosomal DNA. However, this Myxobolus sp. was also similar to Myxobolus hani Faye, Kpatcha, Diebakate, Fall and Toguebaye, 1999, which was described from white mullets in Senegal, Africa, without molecular identification (Faye et al. 1999). Therefore, this current work makes observations on these Myxobolus spp. which are morphologically and biologically similar, and that could establish M. curemae as a junior synonymy of M. hani.

Synopsis of the aurantiactinomyxon collective group (Cnidaria, Myxozoa), with a discussion on the validity of morphotype definition and demise of guyenotia.

Aurantiactinomyxon is one of the most diverse myxozoan collective groups, comprising types that mostly infect freshwater and marine oligochaetes belonging to the family Naididae Ehrenberg, 1828, but also Lumbriculidae Claus, 1872. In this study, a comprehensive revision of all known aurantiactinomyxon types is performed and highlights the fallibility of using the form and length of the valvular processes as main criterion for differentiating among style-less actinospore morphotypes. The demise of the guyenotia collective group is proposed based on the ambiguous features of several types that allow conformity with both the aurantiactinomyxon and guyenotia definitions. Nonetheless, the information presently available clearly shows that a general shift is needed in our approach to actinospore grouping, which should probably be based on actinospore functionality relative to environment and host ecology, rather than on morphology. Life cycle studies based on experimental transmission and molecular inferences of the 18S rDNA have linked aurantiactinomyxon (including former guyenotia) to myxozoans belonging to a diverse array of genera, including Chloromyxum, Henneguya, Hoferellus, Myxobolus, Paramyxidium, Thelohanellus and Zschokkella. This undoubtedly shows a high capacity of the aurantiactinomyxon morphotype to promote infection in intrinsically distinct vertebrate hosts and environmental habitats, consequently increasing interest in its study for attaining a better understanding of myxozoan-host interactions. The identification of novel and known types, however, is impeded by the lack of concise information allowing a comprehensive analysis of biological, morphological, and molecular criteria. In this sense, the compilation of data presented in this study will ultimately help researchers seeking to perform reliable identifications.

Synopsis of myxosporean species (Cnidaria: Myxozoa) parasitizing fishes from Vietnam.

This paper provides an updated checklist of species-level identified myxosporeans from marine and freshwater fishes in Vietnam. The list includes 51 nominal species (38 marine and 13 freshwater) belonging to 9 genera: Myxobolus Bütschli, 1882 (26 species); Kudoa Meglitsch, 1947 (6 species); Henneguya Thélohan, 1892 (6 species); Thelohanellus Kudo, 1933 (5 species); Unicapsula Davis, 1924 (2 species); Ceratomyxa Thélohan, 1892 (2 species), Zschokkella Auerbach, 1909 (2 species); Auerbachia Meglitsch, 1960 (1 species), and Meglitschia Kovaleva, 1988 (1 species). For each parasite species, information on myxospore morphology, line drawings, fish hosts, infection sites, and collection locality in Vietnam are reported. Where available, we also provide GenBank accession numbers for nucleotide sequence data. In addition, taxonomic status of several species was discussed and Myxobolus eszterbaueri nom. nov. is proposed as a junior homonym for Myxobolus hakyi Baska, Voronin, Eszterbauer, Müller, Marton & Molnár 2009, which is preoccupied.

The myxozoan parasite Myxobolus bejeranoi (Cnidaria: Myxozoa) infection dynamics and host specificity in hybrid tilapia aquaculture.

Nile × blue tilapia hybrid (Oreochromis niloticus × O. aureus) has become an important food fish in intensive freshwater aquaculture. Recently, the parasite Myxobolus bejeranoi (Cnidaria: Myxozoa) was found to infect hybrid tilapia gills at high prevalence, causing immune suppression and high mortality. Here, we explored additional characteristics of M. bejeranoi­tilapia interaction, which enable efficient proliferation of this parasite inside its specific host. Highly sensitive quantitative polymerase chain reaction (qPCR) and in situ hybridization analyses of fry collected from fertilization ponds provided evidence to an early-life infection of fish by a myxozoan parasite, occurring less than 3 weeks post-fertilization. Because Myxobolus species are highly host-specific, we next compared infection rates in hybrid tilapia and in both its parental species following a 1-week exposure to infectious pond water. Analysis by qPCR and histological sections showed that while blue tilapia was as susceptible to M. bejeranoi as the hybrid, Nile tilapia appeared to be resistant. This is the first report of differential susceptibility of a hybrid fish vs its parental purebreds to a myxozoan parasite. These findings advance our understanding of the relationship between M. bejeranoi and tilapia fish and raise important questions regarding the mechanisms that allow the parasite to distinguish between very closely related species and to infect a specific organ at very early-life stages.

A new species of Myxobolus (Cnidaria: Myxosporea: Myxobolidae) from the gibel carp Carassius gibelio (Cypriniformes: Cyprinidae).

Myxobolus zhaltsanovae n. sp., is described from the gills of gibel carp Carassius gibelio found during a survey of myxozoans from the watershed of Lake Baikal, Russia, based on morphological and molecular characterizations. Plasmodia of M. zhaltsanovae n. sp. develop extravascularly and measure 500-1000 µm long, 25-100 µm wide. The myxospore is circular to oval, measuring 13.23 ± 0.09 (11.3-14.8) µm (mean ± SD, range) in length, 10.19 ± 0.07 (9.1-11.4) µm in width, and 6.49 ± 0.12 (5.4-7.2) µm in thickness. Polar capsules are unequal and subspherical; measurements of polar capsules are: length 5.62 ± 0.06 (4.7-6.7), width 3.44 ± 0.04 (2.4-4.4) µm and length 3.42 ± 0.05 (2.5-4.1), width 1.94 ± 0.04 (1.3-3.3) µm. Phylogenetic analysis with the 18S rDNA gene shows M. zhaltsanovae n. sp. as a sister species of the subclade formed by M. musseliusae, M. tsangwuensis, and M. basilamellaris, which infect common carp Cyprinus carpio.

A new Myxobolus (Cnidaria: Myxosporea: Myxobolidae) from the gills of the southern striped shiner, Luxilus chrysocephalus isolepis (Cypriniformes: Leuciscidae), from southwestern Arkansas, USA.

The southern striped shiner, Luxilus chrysocephalus isolepis (Hubbs & Brown) is a relatively large minnow belonging to the true minnow family Leuciscidae Bonaparte. Between May 2020 and January 2022, 55 L. c. isolepis were collected from watersheds in Montgomery (n = 6), Polk (n = 17) and Sevier (n = 32) counties, Arkansas, USA, and their gills, gallbladders, urinary bladders, fins, integument, other major organs, and musculature were examined for myxozoans. Gills of 11 (34%) individual southern striped shiners from Sevier County were infected with a new myxozoan, Myxobolus carlhubbsi n. sp. A qualitative and quantitative morphological description was based on formalin-fixed preserved myxospores, and molecular data consisted of a 1,970 base pair sequence of the partial small subunit rRNA gene from ethanol-preserved specimens. Histologically, plasmodia filled and expanded interlamellar troughs. Hyperplastic epithelial and goblet cells filled interlamellar troughs adjacent to plasmodia, but inflammatory response was limited to scattered lymphocytes. Phylogenetic analysis revealed that M. carlhubbsi n. sp. is a member of a clade of species with pyriform myxospores parasitizing North American Pogonichthyinae Girard and North American and Eurasian Leuciscinae Bonaparte. This is the first report of a myxozoan from L. c. isolepis. This article was registered in the Official Register of Zoological Nomenclature (ZooBank) as urn:lsid:zoobank.org:pub:D10D71C2-2C75-4A1C-80ED-B98FF36CB509.

A NEW SPECIES OF MYXOBOLUS (CNIDARIA: MYXOSPOREA: MYXOBOLIDAE) FROM THE FINS OF THE WESTERN CREEK CHUBSUCKER, ERIMYZON CLAVIFORMIS (CYPRINIFORMES: CATOSTOMIDAE), FROM ARKANSAS.

Between November 2018 and December 2021, 35 juvenile and adult Western Creek Chubsuckers, Erimyzon claviformis, were collected from 5 sites in western and southern Arkansas (Ouachita and Red River drainages), and their gills, gallbladders, fins, integument, other major organs, and musculature were examined for myxozoans. The fins of 12 (34%) individuals were infected with a novel species, Myxobolus stuartae n. sp. Qualitative and quantitative morphological data were obtained from formalin-fixed preserved myxospores. Molecular data from ethanol-preserved specimens consisted of a 2,028 base pair sequence of small subunit (SSU) ribosomal DNA (rDNA) from a specimen collected in Nevada County. Three other specimens from Polk County yielded partial SSU rDNA sequences that were identical to the first sequence. Phylogenetic analyses placed M. stuartae n. sp. as sister to Myxobolus bibullatus (Kudo, 1934), both clustering with other catostomid-infecting myxobolids. This is the first fin-infecting myxozoan reported from E. claviformis.

A NEW SPECIES OF MYXOBOLUS (CNIDARIA: MYXOSPOREA: MYXOBOLIDAE) FROM THE GILLS OF CREEK CHUB, SEMOTILUS ATROMACULATUS (CYPRINIFORMES: LEUCISCIDAE: PLAGIOPTERINAE), FROM THE OUACHITA DRAINAGE OF ARKANSAS.

During October and November 2021, 33 creek chubs, Semotilus atromaculatus, were collected from 3 sites in Polk County, Arkansas (Ouachita River drainage), and their gills, gallbladder, fins, integument, musculature, and other major organs were examined for myxozoans. The gills of 9 (27%) were infected with a new myxozoan, Myxobolus fountainae n. sp. Qualitative and quantitative morphological data were from fresh and formalin-fixed preserved spores, while molecular data consisted of a 1918 base pair sequence of the partial small subunit ribosomal RNA gene. Phylogenetic analysis grouped M. fountainae n. sp. with the other leuciscid-infecting myxobolids from North America and within a larger clade of European myxozoans. In addition, histological information is provided on the infection. A previous record of Myxobolus muelleriBütschli, 1882, from the gills and ureters of S. atromaculatus is considered invalid and represents an unknown species. Myxobolus fountainae n. sp. is the only named myxozoan known to infect the gill filaments of S. atromaculatus, whereas Myxobolus pendula (Guilford, 1967) infects the gill arches.

Immunosuppression and apoptosis activation mediated by p53-Bcl2/Bax signaling pathway -The potential mechanism of goldfish (Carassius auratus Linnaeus) gill disease caused by Myxobolus ampullicapsulatus.

Myxobolus, a major harmful type of myxospora, is one of the main parasitic pathogens of freshwater fish. Once myxoboliosis occurs, treatment can be extremely difficult. Therefore, clear understandings of the etiology of myxoboliosis and its pathological mechanism are keys for prevention and control. Here, histology, transmission electron microscopy, transcriptome study, tunel assay, and immunohistochemistry were carried out, revealing the morphology, pathological effects as well as host response mechanism of goldfish gill to Myxobolus ampullicapsulatus. Histological studies showed that the mature spores of Myxobolus ampullicapsulatus were composed of three parts, the spore shell, sporoplasm and bottle shaped polar capsule containing double S-shaped polar filaments. Transcriptome analysis revealed that Myxobolus ampullicapsulatus -infected (Myx) goldfish gills were characterized by apoptosis activation mediated by "p53 signaling pathway" with significantly up-regulated apoptosis-related differential genes dominated by p53-Bcl2/Bax signaling pathway. In addition, tunel assay revealed severe gill apoptosis in the Myx group. Transcriptome analysis also revealed that Myx group showed changes in immune response and significantly down-regulated immune-related differential genes. Beyond that, immunohistochemistry showed that there was no significant increase in the number of gill lymphocyte after parasite infection. These results suggest that the pathological mechanism of Myxobolus ampullicapsulatus infection on gills of goldfish may be related to apoptosis and immunosuppression. Subsequent qRT-PCR showed that apoptosis-related genes (Caspase3,Bad, Bax) and anti-inflammatory gene IL-10 were significantly increased, while immune-related pro-inflammatory genes (IL-1ß, IL-8) were markedly down-regulated, further verifying the transcriptome results. Based on the above results, we concluded that p53-Bcl2/Bax related networks that dominant the expression of apoptosis genes were activated while immunity was suppressed in the gills of Myxobolus ampullicapsulatus infected goldfish. Our study is not only of benefit to enrich the taxonomy of Myxobolus but also clarifies its pathogenic mechanism, thus providing targets for prevention and control of myxoboliosis.