A NOVEL SPECIES OF MYXOBOLUS (CNIDARIA: MYXOSPOREA: MYXOBOLIDAE) FROM THE GILL OF GREEN SUNFISH, LEPOMIS CYANELLUS (PERCIFORMES: CENTRARCHIDAE), FROM THE BLACK RIVER OF NORTHEASTERN ARKANSAS.

During March 2023, 7 green sunfish (Lepomis cyanellus) and 2 bluegill (Lepomis macrochirus) were collected from the Black River (White River drainage) in Lawrence County, Arkansas. In addition, during March 2023 and again in May-June 2023, 13 L. cyanellus and 6 L. macrochirus were taken from Butcherknife and Big Fork creeks (Ouachita River drainage), Polk County, Arkansas, 9 L. cyanellus were collected from the Caddo River, Montgomery County, Arkansas, and 5 green sunfish were taken from Clear Creek at Savoy, Washington County, Arkansas. All fish had their gill, gallbladder, fins, integument, musculature, and other major organs examined for myxozoans. The gill of 1 of 34 (3%) L. cyanellus was infected with a new myxozoan, Myxobolus fergusoni n. sp. Qualitative and quantitative morphological data were obtained from fresh myxospores, and molecular data consisted of a 1,933-base-pair sequence of the partial small subunit (SSU) ribosomal RNA (rRNA) gene. Phylogenetic analysis grouped M. fergusoni n. sp. with other centrarchid-infecting myxobolids from North America and placed this cluster in a larger clade comprising myxozoans that infect North American and European esocids, a North American aphredoderid, European percids, and a gasterosteid from Japan. Myxobolus fergusoni n. sp. infects the gill arches of L. cyanellus, similar to Myxobolus cartilaginis (Hoffman, Putz, and Dunbar, 1965), which was described from head cartilage, gill arches, and large fin rays of L. cyanellus. Another is Myxobolus mesentericusKudo, 1920, which was described from the viscera of green sunfish. A large polysporic plasmodium filled with myxospores was present in a basifilamental location associated with multiple gill filaments at their junction with the gill arch. The intact plasmodium replaced connective tissue within the arch but elicited only mild proliferation of overlying epithelium and a minimal host inflammatory response. This is the third time a myxozoan has been described from L. cyanellus, as well as being the first time it has been described from an Arkansas specimen.

New species of Myxobolus in potamodromous catfish from the eastern Amazon, Brazil.

The mapará (Hypophthalmus marginatus) is a commercially important fish in the Brazilian Amazon and has been described as a host for numerous myxosporid species. The integrated taxonomy of a new species, Myxobolus mickeyii n. sp., discovered in the urinary bladder of H. marginatus, is undertaken in this study. In 105 specimens of H. marginatus, plasmodia and myxospores were observed in the urinary bladder fluid, the myxospores measuring 20.5 (19.6-21.3) µm in length and 14.0 (13.2-14.9) µm in width. The posterior valves of the spore body were thick, with valvulogenic nuclei, endoplasmic reticulum, and the presence of secretory vesicles. Two elliptical, rounded appendages attached to the valve, containing tubular filaments. The two polar capsules, symmetry, measuring 6.1 (5.9-6.3) µm in length and 4.4 (3.6-6.2) µm in width, with polar tubules of 3 to 5 turns. Phylogenetic analyses of the small subunit ribosomal RNA gene (SSU rDNA) sequencing revealed that M. mickeyii n. sp. is part of a Myxobolidae family clade with freshwater fish of the Siluriformes order, with a genetic distance of 19% to the nearest species. This work contributes to the wide diversity of myxozoans in this host, as other taxa have previously been reported infecting different tissues.

Occurrence of Myxobolus spp. (Myxozoa) in the blood of Metynnis lippincottianus (Osteichthyes: Serrasalmidae) from eastern Amazon, Brazil.

Myxozoans are obligatory parasites and can be found in various organs and bloodstreams of fish, thus, the objective of this work was to describe the occurrence of Myxobolus spp. in the circulating blood of Metynnis lippincottianus from River Curiaú, Macapá City, eastern Amazon, Brazil. The samples of M. lippincottianus (11) were caught using cast net and gillnets. The fish blood was collected by puncturing the caudal vessel, using needles and syringes containing 10% of EDTA solution. Blood smear were prepared and panchromatic stained with a combination of May Grunwald-Giemsa-Wright, for observation and examination of the parasitic structures in optical microscope. Tissues from the kidney was examined using specific stereoscopic binoculars to check for the presence of cysts, lesions and parasites. The prevalence of Myxobolus spp. infecting the circulating blood of the fish was 36.36% (4/11) and 15 spores of mixosporyds were visualized. Myxobolus spp. had a prevalence of 54.55% (6/11) in host's kidney tissue and the morphometric spores data converge with observed in the blood. The morphological characteristics of the spores in the blood samples revealed two morphotypes of Myxobolus spp. This is the sixth occurrence recorded of Myxobolus spp. infecting fish blood in Brazil.

Scoliosis and kyphosis in blue-spotted and marbled flathead fish associated with a Myxobolus acanthogobii-like parasite.

Spinal deformities in finfish have the potential to impact aquaculture industries and wild populations by increasing morbidity, mortality, and reducing growth rates. Myxobolus acanthogobii has been implicated in causing scoliosis and lordosis in various aquatic species in Japan. We investigated 4 cases of spinal deformity in 2 flathead (Platycephalus) species that were submitted to the Elizabeth Macarthur Agricultural Institute (EMAI) in New South Wales (NSW), Australia, between 2015 and 2021. Flathead are commercially significant species that are popular among Australian consumers, and are also sought-after species targeted by recreational fishers. Gross deformities are concerning to the community and may impact the quality and quantity of specimens available for consumption. Three blue-spotted flathead (P. caeruleopunctatus) and one marbled flathead (P. marmoratus) were submitted, all with marked scoliosis and kyphosis; 1-2-mm cysts were present on the dorsum of the brain, most often over the optic lobe or cerebellum. Cytology and differential interference microscopy of cyst material revealed numerous oval spores, x̄ 14 ± SD 0.75 µm × x̄ 11.5 ± SD 0.70 µm, with 2 pyriform polar capsules, the morphology of which is consistent with a Myxobolus sp. PCR assay and 18S rDNA sequencing of the cyst material identified a Myxobolus sp. with 96% identity to M. acanthogobii. The identification of this Myxobolus sp. confirms the presence of parasites with the potential to cause spinal deformity in significant aquatic species in NSW waterways.

A NEW SPECIES OF MYXOBOLUS (CNIDARIA: MYXOSPOREA: MYXOBOLIDAE) FROM THE BLUE SUCKER, CYCLEPTUS ELONGATUS (LESUEUR) (CYPRINIFORMES: CATOSTOMIDAE: CYCLEPTINAE), FROM ARKANSAS.

During 9-10 February 2018 and 21-22 February 2020, 7 adult Blue Suckers, Cycleptus elongatus, were collected by hoop nets from the Red River, Little River County (n = 3), and the Black River, Lawrence County (n = 4), Arkansas, and their gills, gallbladders, fins, integument, other major organs, and musculature were examined for myxozoans. All 7 (100%) were infected with an unknown species of gill-infecting Myxobolus sp. Twenty formalin-fixed plasmodia (cysts) of Myxobolus cloutmani n. sp. were elliptoidal, 407 µm long × 270 µm wide. Formalin-fixed myxospores were orbicular to broadly elliptoidal, 8.7 µm long × 7.8 µm wide. Two polar capsules were pyriform and subequal in size, extending over halfway in the myxospore. The larger polar capsule was 5.5 µm long × 3.1 µm wide, while the shorter was 5.1 × 2.9 µm. A coiled polar filament possessed 5 or 6 coils. The myxospore was 3.7 µm thick in sutural view, with a distinct sutural ridge. Qualitative and quantitative morphological data were from formalin-fixed as well as ethanol-preserved spores, while molecular data consisted of a 2,010 base pair sequence of the partial 18S ribosomal RNA gene and a 2,502 base pair sequence of the partial 28S ribosomal RNA gene. Phylogenetic analysis grouped M. cloutmani n. sp. with the other catostomid-infecting myxobolids. This is the first myxozoan reported from C. elongatus.

Molecular data and phylogenetic analysis of Myxobolus pseudonobilis n. sp. infecting the gill filaments of silver carp, Hypophthalmichthys molitrix Valenciennes, 1844.

In the present study, we combined morphological and phylogenetic methods to characterize Myxobolus pseudonobilis n. sp. infecting Hypophthalmichthys molitrix Valenciennes, 1844 from Chongqing, China. The morphology and molecular characteristics of M. pseudonobilis n. sp. were distinct from those of other previously described Myxobolus species. Mature myxospores were ovoid in frontal view with spore dimensions of 10.0 ± 0.4 (9.3-10.9) µm in length and 8.5 ± 0.2 (7.9-9.0) µm in width. Two polar capsules occupying approximately half of the myxospore length were unequal in size. The larger polar capsule containing 6 to 7 filament coils measured 5.2 ± 0.3 (4.5-5.8) µm in length and 3.6 ± 0.2 (3.2-3.9) µm in width, while the smaller capsule with 4 to 5 filament coils measured 3.9 ± 0.3 (3.0-4.4) µm in length and 2.5 ± 0.3 (2.1-3.6) µm in width. The comparison of molecular characteristics demonstrated similarities and genetic distances of 18S rDNA sequences of 95.19% - 98.20% and 1.82% - 5.46%, respectively, between M. pseudonobilis n. sp. and its morphologically similar species, and secondary structures were also distinctly different. Moreover, phylogenetic analysis showed that M. pseudonobilis n. sp. was clustered with other myxobolids possessing spores with a blunt anterior end and branched independently. In addition, the morphology of myxosporeans as an important indicator was discussed.

Increasing the known biodiversity of cnidarian parasites of bryconid fishes from South America: two novel Myxobolus species with ultrastructure and ssrDNA-based phylogeny.

This study increases the known biodiversity of cnidarian parasites in neotropical bryconid fishes. Two novel Myxobolus species are described based on morphology, ultrastructure and small subunit ribosomal DNA (ssrDNA) sequencing: Myxobolus vetuschicanus n. sp. infecting fins of Salminus franciscanus and Myxobolus mineirus n. sp. infecting the mesentery of Brycon orthotaenia from the São Francisco River basin, Minas Gerais State, Brazil. Ultrastructural analysis of the two species revealed an asynchronous sporogenesis process, with germinative cells and young developmental stages of myxospores in the periphery of the plasmodia. In M. vetuschicanus n. sp., the plasmodia were surrounded by a layer of fibroblasts and in M. mineirus n. sp., the plasmodial membrane had direct contact with the host tissue. The phylogenetic analysis based on the ssrDNA of Henneguya/Myxobolus species showed that the two novel Myxobolus species grouped in subclades together with other parasite species of bryconid fishes.

First report of Myxobolus episquamalis Egusa, Maeno & Sorimachi, 1990 (Myxozoa: Bivalvulida) in Lebranche mullet Mugil liza Valenciennes, 1836 (Teleostei: Mugiliformes) from Neotropical region.

In the current study, Myxobolus episquamalis Egusa, Maeno & Sorimachi, 1990 (Myxozoa: Bivalvulida) is reported from the Lebranche mullet Mugil liza Valenciennes, 1836 in the estuarine region of the Maricá Lagoon, State of the Rio de Janeiro, southeastern Brazil. To date, this myxozoan species was reported in mullets from Asia, Africa, Europe, and Oceania. The characteristics of M. episquamalis previously reported are similar to the findings of the present study. DNA sequences of the nuclear small subunit ribosomal DNA (SSU rDNA) had 99.7-100% similarity with the sequences of M. episquamalis from North Africa and Asia. Therefore, strong morphological and molecular similarities ensure the identification of M. episquamalis in the current study. Finally, this finding records a new host and locality, revealing the worldwide distribution of this myxozoan species.

An updated geographic distribution of Myxobolus cerebralis (Hofer, 1903) (Bivalvulida: Myxobolidae) and the first diagnosed case of whirling disease in wild-caught trout in the south-eastern United States.

Myxobolus cerebralis (Bivalvulida: Myxobolidae), the aetiological agent of salmonid whirling disease, was detected in 2 river basins of North Carolina during 2015, which initiated the largest spatial-temporal monitoring project for the disease ever conducted within the south-eastern United States (focused mainly in eastern Tennessee and western North Carolina). A total of 2072 rainbow trout Oncorhynchus mykiss, 1,004 brown trout Salmo trutta and 468 brook trout Salvelinus fontinalis were screened from 113 localities within 7 river basins during June 2017 through October 2019. Infections were detected by pepsin-trypsin digest, microscopy and the species-specific nested polymerase chain reaction (PCR) in 19 localities across 6 river basins. Myxospore morphology was indistinguishable from the published literature. In 2019, five rainbow trout that symptomatic for whirling disease (sloping neurocranium and lordosis) were captured and processed for histopathology. Myxospores were detected in the calvarial cartilage of two deformed trout with associated erosion of the cartilage consistent with reported whirling disease lesions. This is the first report of M. cerebralis in Tennessee and the first histologically confirmed cases of whirling disease in southern Appalachian (south-eastern United States) rivers and streams and expands the distribution of M. cerebralis throughout western North Carolina and eastern Tennessee.

Involvement of sphaeractinomyxon in the life cycle of mugiliform-infecting Myxobolus (Cnidaria, Myxosporea) reveals high functionality of actinospore morphotype in promoting transmission.

Four new actinospore types belonging to the sphaeractinomyxon collective group (Cnidaria, Myxosporea) are described from the coelomic cavity of a marine Baltidrilus sp. (Oligochaeta, Naididae) inhabiting a northern Portuguese estuary. Host identification supports the usage of marine oligochaetes, namely of the family Naididae Ehrenberg, 1828, as definitive hosts for myxosporeans inhabiting estuarine/marine environments. The absence of mixed infections in the host specimens analysed is suggested to reflect the influence of host-, parasite- and environmental-related factors regulating myxosporean-annelid interactions. Molecular analyses matched the SSU rDNA sequences of three of the four new types with those of mugiliform-infecting Myxobolus spp., namely Myxobolus mugiliensis and a Myxobolus sp. from flathead grey mullet Mugil cephalus, and Myxobolus labrosus from thicklip grey mullet Chelon labrosus. These results directly link, for the first time, the sphaeractinomyxon collective group to a myxospore counterpart, further confirming their previously hypothesized specific involvement in the life cycle of myxobolids that infect mullets. Acknowledging this life cycle relationship, the functionality of the sphaeractinomyxon morphotype is suggested to have been decisive for the evolutionary hyperdiversification of the genus Myxobolus in mullets. Unlike other actinospore morphotypes, sphaeractinomyxon lack valvular processes, which implies a limited capability for buoyancy. Considering the benthic-feeding nature of mullets, this feature is most likely crucial in promoting successful transmission to the vertebrate host.

Common dace (Leuciscus leuciscus) - A new host of the myxozoan fish parasite, Myxobolus elegans (Cnidaria: Myxozoa) - Short communication.

This paper reports the detection of the myxozoan species Myxobolus elegans Kashkovsky 1966 in common dace (Leuciscus leuciscus) that has not been previously listed as its host. The problem of differentiation of phenotypically similar Myxobolus species is addressed. During parasitological survey of common dace from the desalinated part of the Gulf of Finland at the city of Sestroretsk, Russia, numerous oval-shaped plasmodia, 0.2-0.4 mm in size, filled with Myxobolus spores were found on the gills. Pear-shaped myxospores were 15.4 (14.8-16.0) × 10.2 (9.6-10.9) µm in size with a rib on each valve. On the basis of spore morphology, the species appeared to be similar to M. elegans and Myxobolus hungaricus Jaczó, 1940. In order to identify the species, molecular genetic analysis was performed, and the species was identified on the basis of morphological characteristics and 18S rDNA data. The results obtained indicate that the Myxobolus species observed on the gills of dace is M. elegans. Thus, common dace is another valid host of M. elegans besides the type host, ide (Leuciscus idus).

Novel myxosporean species parasitizing an economically important fish from the Amazon basin.

This paper provides morphological and phylogenetic analyses of two new myxobolid species found infecting Piaractus brachypomus from the Amazon basin. The fish were caught in the Tapajós River, in the municipality of Santarém, in the state of Pará, Brazil. The plasmodial development of Henneguya brachypomus n. sp. occurred in the gill lamellae while Myxobolus pirapitingae n. sp. developed in the pyloric cecum. Morphological analyses did not identify inflammatory infiltrate for either species, but H. brachypomus n. sp. induced stretching of the epithelium, compression of the adjacent tissues, and displacement and deformation of the neighboring lamellae. The mature myxospores of H. brachypomus n. sp. were ellipsoid, with a length of 11.7-13.8 µm, a width of 4.0-4.6 µm, and a thickness of 3.5-4.3 µm. The polar capsules were elongated, with a length of 5.6-7.3 µm and a width of 1.3-2.0 µm, and each contained a polar filament with 8-9 coils. The caudal process was 40.5-48.1 µm long and the total length of the myxospore was 52.4-61.6 µm. Myxobolus pirapitingae n. sp. exhibited rounded mature myxospores measuring 10.0-11.1 µm in length, 7.0-7.6 µm in width, and 5.4-6.3 µm in thickness. The polar capsules were of equal size and occupied less than half the myxospore, measuring 3.5-4.0 µm in length and 2.0-2.6 µm in width, with each containing a polar filament with 6-7 coils. Phylogenetic analysis based on partial small subunit ribosomal DNA (ssrDNA) sequences showed that H. brachypomus n. sp. clustered as a sister species of Henneguya piaractus, while M. pirapitingae n. sp. was grouped in a sub-clade together with Myxobolus matosi and Myxobolus colossomatis.

Myxobolus spp. (Cnidaria: Myxozoa) in introduced yellow perch Perca flavescens (Mitchill, 1814).

We surveyed introduced yellow perch Perca flavescens (Mitchill, 1814) from the Willamette River, OR, USA, to determine if these fish have co-introduced myxosporean parasites. Mature parasite myxospores were observed in brains of 3/19 fish, and were morphologically and molecularly consistent with Myxobolus neurophilus (Guilford 1963), a parasite known from yellow perch in their native range. We identified another Myxobolus species from the gill filaments of 1/22 fish. The spores from the gill filaments were oval-shaped, 11.7 (10.7-12.3) µm long × 8.6 (7.7-9.0) µm wide × 5.2 (4.6-5.6) µm thick, with two oval-shaped polar capsules 5.7 (5.1-6.5) µm × 2.7 (2.4-3.2) µm, each containing a polar tubule with 8-9 turns. Small-subunit ribosomal DNA sequences from each of four plasmodia were identical, and 4.0% different (over 1800 nucleotides) from the closest known myxosporeans. Interestingly, these sequences had overlapping peaks in their chromatograms, which suggested that DNA from multiple species was present. Hence, we isolated and sequenced three individual myxospores and found that they too had mixed chromatograms, which indicated presence of at least two sequence types of small-subunit ribosomal DNA in each spore (GenBank accession MK592012, MK592013), a rare character among described myxosporeans. The spore morphology, morphometry, tissue tropism, and DNA sequence supported a diagnosis of a novel species, Myxobolus doubleae n. sp. This parasite is unknown from yellow perch in its native range, despite extensive historical surveys, which suggests that introduced yellow perch might have acquired an endemic Myxobolus species via spillback from another fish host.

Ultrastructural morphology of the Myxobolus dermatobius Ishii 1915 (Mixosporea: Myxobolideae) microspores infecting eyes of Nile tilapia (Oreochromis niloticus) in Egypt.

A total of 1,000 cultured Nile tilapia (Oreochromis niloticus) were collected from different governmental and private fish farms and examined for detection of myxosporean parasites infection. The infected fishes showed slight unilateral exophthalmia with whitish cyst in the eye. Numerous white cysts like plasmodia of Myxobolus dermatobius were recovered from the eye of the examined fishes with low prevalence rate (1%). Small intact cyst was isolated, fixed in 3% glutaraldehyde in 0.1 M sodium cacodylate (pH 7.4) and prepared for transmission electron microscopy examination. Ultrathin sections myxospores of M. dermatobius revealed pair of capsulogenic cells at the apical pole of the developing myxospore. Single sporoplasm containing a single nucleus and sporoplasmosomes fills nearly all the space beneath the polar capsules. The later were pyriform in shape, each one had homogenous dense core and 4 turns of polar filaments. Ultrastructural characteristics of the present myxospore were described and discussed in detail.

Myxobolus sp. (Myxozoa; Myxosporea) causing asymptomatic parasitic gill disease in Astyanax aff. bimaculatus (Characiformes; Characidae) in the Tocantins river basin, amazon region, Brazil / Myxobolus sp. (Myxozoa; Myxosporea) causando doença parasitária assintomática nas brânquias em Astyanax aff. bimaculatus (Characiformes; Characidae) na bacia do rio Tocantins, região amazônica, Brasil

Abstract The middle course of the Tocantins river is located in the eastern portion of the "Legal Amazon" region of Brazil and the Dantas river is one of its tributaries. Among the components of the aquatic biota, eukaryote microparasites establish direct relationships with several species of fish and have zoonotic potential that is still little known. Myxozoans stand out among these parasites: they cause myxosporidiosis, a disease that gives rise to high mortality rates worldwide. The genus Myxobolus accounts for the largest number of species that have been described. Thirty specimens of Astyanax aff. bimaculatus that had been caught in the Dantas river were examined. The prevalence of cysts with spores morphologically compatible with myxozoans of the genus Myxobolus in the arcuate and gill filaments of these specimens was 20%.

Resumo O curso médio do rio Tocantins está localizado na porção leste da região da "Amazônia Legal" do Brasil, e o rio Dantas é um dos seus afluentes. Dentre os componentes da biota aquática, os microparasitos eucarióticos estabelecem relações diretas com várias espécies de peixes e possuem potencial zoonótico ainda pouco conhecido. Os mixozoários destacam-se entre esses parasitos causando mixosporidiose, doença que dá origem a altas taxas de mortalidade em todo o mundo. O gênero Myxobolus é responsável pelo maior número de espécies descritas de mixozoários. Trinta espécimes de Astyanax aff. bimaculatus capturados no rio Dantas foram examinados. A prevalência de cistos com esporos morfologicamente compatíveis com mixozoários do gênero Myxobolus nos filamentos arqueados e branquiais desses espécimes foi de 20%.

First Molecular Data on Myxobolus episquamalis (Myxozoa: Myxosporea) Infecting the Scale of Grey Mullet (Mugil cephalus) from Turkey

Objective: The aim of the present study was to show the morphologic and molecular characterization of Myxobolus species in grey mullet (Mugil cephalus) caught from the Black Sea coasts of Turkey. Methods: A total of 104 grey mullets caught from Turkish Black Sea coasts were obtained from fish markets between November 2017 and February 2018 and were examined for the presence of Myxobolus by using morphological and advanced molecular diagnostic methods. Results: Totally, three out of 104 fish specimens were found to be infected with large and white coloured plasmodia and the prevalence was determined as 2.8%. The myxospores were morphologically identified as Myxobolus episquamalis, confirmed by using sequence analyses of their 18S rRNA gene regions. The shape of myxospores was oval and they were 8.6 (7.8-9.4) µm in length, 6.7 (6.1-7.3) µm in width and 4.7 (4.1-5.3) µm in thickness. Measuremenst of two pyriform polar capsules were 4.2 (3.7-4.6) µm in length ve 2.2 (2.1-2.4) µ m in width. The length of polar filament was determined as 27-51 µm. Nucleotide sequences of the 18S rRNA gene of the ES-2018-ERU isolate (MK012069) found in our study showed 99.8% and 100% similarity with M. episquamalis isolates submitted to GenBank from Tunisia (AY129312) and South Korea (JF810537; KC733437), respectively. Pairwise genetic distance (%) between ES-2018-ERU isolate and the other Myxobolus species which were identified in mullets from various countries were determined as 9.9-14.8%. Conclusion: This study provides first molecular Conclusion: This study provides first molecular data on M. episquamalis found in the scale of the grey mullets (Mugil cephalus) from Turkey.

Myxobolus sp. (Myxozoa; Myxosporea) causing asymptomatic parasitic gill disease in Astyanax aff. bimaculatus (Characiformes; Characidae) in the Tocantins river basin, amazon region, Brazil.

The middle course of the Tocantins river is located in the eastern portion of the "Legal Amazon" region of Brazil and the Dantas river is one of its tributaries. Among the components of the aquatic biota, eukaryote microparasites establish direct relationships with several species of fish and have zoonotic potential that is still little known. Myxozoans stand out among these parasites: they cause myxosporidiosis, a disease that gives rise to high mortality rates worldwide. The genus Myxobolus accounts for the largest number of species that have been described. Thirty specimens of Astyanax aff. bimaculatus that had been caught in the Dantas river were examined. The prevalence of cysts with spores morphologically compatible with myxozoans of the genus Myxobolus in the arcuate and gill filaments of these specimens was 20%.

Morphological variation in Myxobolus drjagini (Akhmerov, 1954) from silver carp and description of Myxobolus paratypicus n. sp. (Cnidaria: Myxozoa).

There is uncertainty in the identification of Myxobolus drjagini, the causative agent of silver carp twist disease, in the literature. An investigation of fish parasites in Lake Taihu, China, revealed several Myxobolus drjagini-like myxosporeans infecting the subcutaneous tissue of the head skin, the olfactory and oculomotor nerves in the cranial cavity, and the intrafilamental epithelium of the gills of silver carp Hypophthalmichthys molitrix (Valenciennes, 1844). Myxospores from the head skin and the nerves were identified as conspecific to M. drjagini based on morphological and molecular data; although the spores from each of the two organs presented morphological variations. SSU rDNA sequence analysis revealed that the sequence of M. drjagini previously deposited in GenBank (AF085179) was invalid. Myxospores from the gills were identified as Myxobolus paratypicus n. sp. The spores were oval, asymmetric in frontal view, 13.8 (12.9-14.9) µm long, 9.9 (9.2-11.1) µm wide, and 7.0 µm thick. Two pyriform polar capsules were unequal in size (ratio above 4:1) with slightly converging anterior ends, and the posterior end of the large polar capsule extended beyond the middle of the spore. The large polar capsule was 7.5 (6.2-8.2) µm long and 5.0 (4.2-5.6) µm wide; the small polar capsule was 2.7 (2.1-3.6) µm long and 1.4 (1.1-1.9) µm wide. Polar filaments were coiled with 7-8 turns in the large polar capsule. The SSU rDNA sequence of M. paratypicus n. sp. was not identical to that of any myxozoan available in GenBank and showed highest similarity with M. drjagini (96%) and Myxobolus pavlovskii (95%) collected from bighead carp and silver carp, respectively.

New data on Myxobolus imparfinis (Cnidaria, Myxosporea): host, distribution, and ultrastructural morphology.

A mass of free myxozoan spores was found in the gill filaments of specimens of Cetopsorhamdia iheringi Schubart and Gomes, 1959, popularly known as "three-barbeled catfishes" (Heptapteridae, Siluriformes) collected in streams of the Middle Paranapanema River, Upper Paraná River basin, in the state of São Paulo, Brazil. Morphological and molecular analysis identified the spores as Myxobolus imparfinis Vieira, Tagliavini, Abdallah and Azevedo, 2018. The ultrastructural morphology of this parasite is described here for the first time. Differences were observed in the number of coils of the polar filament as well as some organelles not previously described for this species. Asynchronous development was also observed, with the presence of both mature and immature spores. This is the first report of a myxozoan parasitizing C. iheringi and the first geographical record of myxozoan parasites in streams of the Middle Paranapanema River. The new data improve the original description of the species and add to the knowledge of host-parasite interactions and distribution.

Description of Myxobolus xiantaoensis n. sp. from the fins of yellow catfish in China: a species previously attributed to Myxobolus physophilus Reuss, 1906 in Chinese records.

Myxozoans are economically important cnidarian endoparasites. Members of this group have been traditionally characterized by a morphology-based taxonomic system. Because myxozoans possess few morphological characters, these data are routinely accompanied by biological traits (host/organ/tissue specificity) and molecular data when describing or identifying myxozoan species. In the present study, a species of Myxobolus was collected from the fins of yellow catfish Tachysurus fulvidraco Richardson, 1846, which was consistent in spore morphology and host/organ specificity with Chinese records of Myxobolus physophilus Reuss, 1906. However, these earlier records and our own findings are inconsistent with the original description of M. physophilus from Russia. Specifically, there are differences in spore morphology (shape, intercapsular appendix, and polar capsule size), the infection site (air bladder vs. fins), and the host affinity (common rudd vs. yellow catfish). The inconsistencies allow us to conclude that both the present Myxobolus species and Chinese records of M. physophilus are distinct from the original description of M. physophilus and represent a new Myxobolus species, which we named Myxobolus xiantaoensis n. sp.