Strategies for describing myxozoan pathogens, dreadful fish diseases in aquaculture.

Myxozoans are obligate endoparasites, cosmopolitan in distribution with both vertebrate and invertebrate hosts. Their myxospores consist of shell valves, polar capsules with coiled polar tubules that are extrudible, and infective amoeboid germs. Myxozoan parasites are most abundant, and due to their increasing number in recent years, they can pose an emerging threat to the fish industry worldwide. Hence, the immediate need is to devise a strategy to understand and detect parasites and parasitism. They may proliferate to different organs with the advancement of infection. This all warrants the development/devising of strategies and results of integrative studies in order to identify these dreadful parasites and resolve taxonomic issues. Different methods whether classical methods including gross morphology or advanced methods such as electron microscopy (SEM, TEM, STEM), Confocal laser scanning microscopy (CLSM), histopathological studies, site preference, host and tissue specificity, a molecular approach using new markers can be clubbed for identification because these parasites are hidden and are difficult to recognize. This group was earlier classified only on the basis of myxospores morphology, but due to the high structural variability of this group advanced methods and approaches have to be implied which can minimize the problems in assigning new species.

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.

Characterizing Two New Henneguya Species in the Respiratory Organs of African Sharptooth Catfish.

Henneguya species are myxozoans, a suborder of Cnidaria, which can affect the gills and extrarespiratory organs of the African sharptooth catfish, Clarias gariepinus. This research describes natural infection-induced histological alterations caused by the Henneguya species present. The Henneguya species were also identified molecularly using DNA sequenced from infected tissue cysts, and phylogenetically analyzed. Clinical investigations revealed cyst-like nodules on the fish gill filaments and extrarespiratory organs. Within a milky fluid inside the cysts were several Henneguya-like spores. Henneguya sp. infested 27.5% of the fish, with the highest prevalence in the gills compared to the extrarespiratory organs. The Henneguya species parasitized the gill and the dendritic tissues, resulting in histopathological characteristics. The plasmodia's developmental stages resulted in destructive damage which manifested as marked necrosis, which was replaced by a focal aggregation of inflammatory cells. Amplification of the 18S ribosomal DNA from the fish parasites was followed by sequencing, which confirmed their identities as new species Henneguya qenabranchiae n. sp. and Henneguya qenasuprabranchiae n. sp. with 99.53 and 99.64% identities, respectively, to Henneguya sp. 1 HS-2015. The two C. gariepinus myxozoans shared some characteristics based on morphologic and phylogenetic analysis as previously published, where it was proposed that they were a sister lineage to Henneguya species in Egypt, and it is now proposed that they are new species.

Genome-wide alternative splicing profile in the posterior kidney of brown trout (Salmo trutta) during proliferative kidney disease.

BACKGROUND: The cnidarian myxozoan parasite Tetracapsuloides bryosalmonae causes chronic proliferative kidney disease (PKD) in salmonids. This parasite is a serious threat to wild and cultured salmonids. T. bryosalmonae undergoes intra-luminal sporogonic development in the kidney of brown trout (Salmo trutta) and the viable spores are released via urine. We investigated the alternative splicing pattern in the posterior kidney of brown trout during PKD. RESULTS: RNA-seq data were generated from the posterior kidney of brown trout collected at 12 weeks post-exposure to T. bryosalmonae. Subsequently, this data was mapped to the brown trout genome. About 153 significant differently expressed alternatively spliced (DEAS) genes, (delta PSI = 5%, FDR P-value < 0.05) were identified from 19,722 alternatively spliced events. Among the DEAS genes, the least and most abundant alternative splicing types were alternative 5' splice site (5.23%) and exon skipping (70.59%), respectively. The DEAS genes were significantly enriched for sodium-potassium transporter activity and ion homeostasis (ahcyl1, atp1a3a, atp1a1a.1, and atp1a1a.5). The protein-protein interaction network analysis enriched two local network clusters namely cation transporting ATPase C-terminus and Sodium/potassium ATPase beta chain cluster, and mixed inclusion of Ion homeostasis and EF-hand domain cluster. Furthermore, the human disease-related salmonella infection pathway was significantly enriched in the protein-protein interaction network. CONCLUSION: This study provides the first baseline information about alternative splicing in brown trout during PKD. The generated data lay a foundation for further functional molecular studies in PKD - brown trout infection model. The information generated from the present study can help to develop therapeutic strategies for PKD in the future.

Kudoa hypoepicardialis and associated cardiac lesions in invasive red lionfish Pterois volitans in Grenada, West Indies.

Invasive red lionfish Pterois volitans (Linnaeus, 1758) represent an ongoing ecological threat within temperate and tropical waters. Relatively little is known regarding the overall health of P. volitans and their potential for spreading pathogens in non-native regions. Lionfish collected from inshore reefs of Grenada, West Indies, in 2019 and 2021 were identified as P. volitans based on cytochrome c oxidase subunit 1 barcoding. Gross and microscopic examination of tissues revealed myxozoan plasmodia in the hearts of 24/76 (31.6%) lionfish by histopathology or wet mount cytology. Further histopathologic examination revealed severe granulomatous inflammation and myofiber necrosis associated with developing plasmodia and presporogonic life stages. Fresh myxospores were morphologically and molecularly consistent with Kudoa hypoepicardialis, being quadrate in apical view with 4 valves and 4 equal polar capsules. The spore body was 5.1-7.9 (mean: 6.0) µm long, 8.1-9.8 (8.7) µm wide, and 6.9-8.5 (7.7) µm thick. Polar capsules were 2.3-2.7 (2.5) µm long and 0.9-1.6 (1.3) µm wide. 18S small subunit rDNA sequences were 99.81-99.87% similar to sequence data from the original description of the species. Novel 28S large subunit rDNA and elongation factor 2 data, which did not match any previously reported species, were provided. This is the first account of a myxozoan parasite of P. volitans, a new host record and locality for K. hypoepicardialis, and one of few reports describing pathogen-associated lesions in invasive lionfish.

A novel myxozoan parasite, Ellipsomyxa boleophthalmi sp. nov. (Myxozoa: Ceratomyxidae) in the brackishwater fish, Boleophthalmus dussumieri Valenciennes, 1837 (Perciformes: Gobiidae) from India.

A novel myxozoan parasite is identified and described from mudskipper, Boleophthalmus dussumieri, collected from a brackishwater ecosystem in Maharashtra, India. Ellipsomyxa boleophthalmi sp. nov. was found in the gallbladder of 58 of 60 fish examined (96.7%). The parasite formed disporous plasmodia that varied in size and shape, and the thin-walled, ellipsoidal and elongated myxospores measured 9.0-10.7 × 6.0-7.8 µm. The two, spherical polar capsules measured 2.7 µm in diameter and enclosed 3-4 coils of polar tubules. Histological observations of infected gallbladder revealed the attachment of disporous plasmodial stages of the parasite to the gallbladder wall with fine pseudopodia. Under the scanning electron microscope (SEM), the myxospores showed a distinct central sutural line and two distinct depressions on the opposite sides at the openings of polar capsules. SEM also revealed the engulfment of microvilli of gallbladder wall by pseudopodia of the plasmodial stages. Analysis of the partial fragment of the SSU rDNA region (1386 bp) showed less than 98% sequence similarity with the other reported Ellipsomyxa spp. In the phylogenetic tree, the present species formed as a distinct subclade within the major clade of Ellipsomyxa spp. The unique morphological and morphometric features of the myxospore, together with the molecular analysis, allowed us to conclude that the present myxozoan is a new species and is named Ellipsomyxa boleophthalmi sp. nov., after the generic name of the host. This is the first report on the occurrence of the genus Ellipsomyxa in B. dussumieri.

Transcriptome Analysis Elucidates the Key Responses of Bryozoan Fredericella sultana during the Development of Tetracapsuloides bryosalmonae (Myxozoa).

Bryozoans are sessile, filter-feeding, and colony-building invertebrate organisms. Fredericella sultana is a well known primary host of the myxozoan parasite Tetracapsuloides bryosalmonae. There have been no attempts to identify the cellular responses induced in F. sultana during the T. bryosalmonae development. We therefore performed transcriptome analysis with the aim of identifying candidate genes and biological pathways of F. sultana involved in the response to T. bryosalmonae. A total of 1166 differentially up- and downregulated genes were identified in the infected F. sultana. Gene ontology of biological processes of upregulated genes pointed to the involvement of the innate immune response, establishment of protein localization, and ribosome biogenesis, while the downregulated genes were involved in mitotic spindle assembly, viral entry into the host cell, and response to nitric oxide. Eukaryotic Initiation Factor 2 signaling was identified as a top canonical pathway and MYCN as a top upstream regulator in the differentially expressed genes. Our study provides the first transcriptional profiling data on the F. sultana zooid's response to T. bryosalmonae. Pathways and upstream regulators help us to understand the complex interplay in the infected F. sultana. The results will facilitate the elucidation of innate immune mechanisms of bryozoan and will lay a foundation for further analyses on bryozoan-responsive candidate genes, which will be an important resource for the comparative analysis of gene expression in bryozoans.

Identification and Expression Profiling of Toll-Like Receptors of Brown Trout (Salmo trutta) during Proliferative Kidney Disease.

Proliferative kidney disease is an emerging disease among salmonids in Europe and North America caused by the myxozoan parasite Tetracapsuloides bryosalmonae. The decline of endemic brown trout (Salmo trutta) in the Alpine streams of Europe is fostered by T. bryosalmonae infection. Toll-like receptors (TLRs) are a family of pattern recognition receptors that acts as sentinels of the immune system against the invading pathogens. However, little is known about the TLRs' response in salmonids against the myxozoan infection. In the present study, we identified and evaluated TLR1, TLR19, and TLR13-like genes of brown trout using data-mining and phylogenetic analysis. The expression pattern of TLRs was examined in the posterior kidney of brown trout infected with T. bryosalmonae at various time points. Typical Toll/interleukin-1 receptor protein domain was found in all tested TLRs. However, TLR13-like chr2 had a short amino acid sequence with no LRR domain. Phylogenetic analysis illustrated that TLR orthologs are conserved across vertebrates. Similarly, a conserved synteny gene block arrangement was observed in the case of TLR1 and TLR19 across fish species. Interestingly, all tested TLRs showed their maximal relative expression from 6 to 10 weeks post-exposure to the parasite. Our results suggest that these TLRs may play an important role in the innate defense mechanism of brown trout against the invading T. bryosalmonae.

Morphology and phylogeny of Henneguya oviperda infecting oocytes of Esox lucius, with description of parasite-induced histopathology.

Henneguya oviperda (Cohn, 1895) (Myxozoa: Myxobolidae) is a parasite infecting oocytes of the northern pike Esox lucius Linnaeus, 1758 (Actinopterygii: Esocidae). Infected oocytes are surrounded by all oocyte layers, some of them thinner and less visible than intact oocytes. A mature plasmodium of H. oviperda fills the entire internal space of the oocytes at the secondary growth phase, rendering the nucleus and organelles of the latter undetectable. Apart from the observed degradation of internal structures, alterations in the envelopes of the infected oocytes, and the deformation of the intact oocytes adjacent to them, no other developmental anomalies have been found in the reproductive products of female northern pike. Mature spores of H. oviperda have oval bodies with polar capsules of almost equal size and caudal projections that are on average equal to the spore body length. Phylogenetic analysis comparing 18S rDNA sequences placed H. oviperda into a clade of esocid-infecting species of the genus Henneguya and also supported H. psorospermica as a sister species.

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.

A new species of Myxobolus (Myxozoa: Bivalvulida) infecting the medulla oblongata and nerve cord of brook trout Salvelinus fontinalis in southern Appalachia (New River, NC, USA).

Myxobolus neurofontinalis n. sp. infects the brain and medulla oblongata of brook trout (Salvelinus fontinalis [Mitchill, 1814]) in the New River, western NC. It is the first species of Myxobolus described from the brook trout and resembles another congener (Myxobolus arcticus Pugachev and Khokhlov, 1979) that infects nerve tissue of chars (Salvelinus spp.). The new species differs from M. arcticus and all congeners by myxospore dimensions and by having a mucous envelope and distinctive sutural markings. A phylogenetic analysis of the small subunit rDNA (18S) suggests that the new species shares a recent common ancestor with some isolates identified as M. arcticus and that the new species and its close relatives (except Myxobolus insidiosus Wyatt and Pratt, 1973) comprise a clade of salmonid nerve-infecting myxobolids. The phylogenetic analysis indicates that several isolates of "M. arcticus" (sensu lato) in GenBank are misidentified and distantly related to other isolates taken from the type host (Oncorhynchus nerka [Walbaum, 1792]) and from nearby the type locality (Kamchatka Peninsula, Russia). Serial histological sections of infected brook trout confirmed that myxospores of the new species are intercellular and infect nerve cord and medulla oblongata only. A single infected brook trout showed an inflammatory response characterized by focal lymphocytic infiltrates and eosinophilic granulocytes; however, the remaining 4 brook trout lacked evidence of a histopathological change or demonstrable host response. These results do not support the notion that this infection is pathogenic among brook trout.

Morphological and molecular characterization of a new species Myxobolus gutturocola n. sp. (Myxozoa: Myxobolidae) from the throat of Hypophthalmichthys molitrix in China.

Myxobolus gutturocola n. sp. was isolated from the throat of silver carp, Hypophthalmichthys molitrix, in Chongqing, China. Myxospore valves are unsymmetrical and smooth. Mature spores are ellipsoidal in frontal view, measuring 12.5 ± 0.2 µm (n = 25) in length, 8.4 ± 0.2 µm (n = 25) in width and 7.1 ± 0.2 µm (n = 25) in thickness. Each spore has two pyriform and unequal sizes polar capsules, the large one with 5.7 ± 0.2 µm in length × 3.6 ± 0.2 µm in width and the small one with 4.6 ± 0.2 µm in length × 2.6 ± 0.1 µm in width. Polar filaments are coiled seven or eight turns in the large polar capsule and four or five turns in the small polar capsule. The coils are arranged almost perpendicularly to the longitudinal axis of the polar capsule. Morphological analysis revealed that M. gutturocola n. sp. is distinct from related species of Myxobolus Bütschli, 1882. Molecular analysis has demonstrated that its SSU rDNA sequences do not match with any available sequences in GenBank. Phylogenetic analysis of the SSU rDNA sequences indicated this species clustered in a clade composed exclusively of parasites infecting the fishes of the Leucisini lineage and most closely related to Myxobolus pavlovskii isolated from the gill filaments of silver carp in Hungary.

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.

Genotyping of individual Ceratonova shasta (Cnidaria: Myxosporea) myxospores reveals intra-spore ITS-1 variation and invalidates the distinction of genotypes II and III.

Genotypes of the myxosporean parasite Ceratonova shasta are defined by the number of ATC repeats in the parasite's ribosomal DNA internal transcribed spacer region 1. These genotypes correlate with specific salmonid fish hosts. We observed coho salmon (Oncorhynchus kisutch) and rainbow trout (Oncorhynchus mykiss) with mixtures of genotypes II and III, and assumed that this was a consequence of fish having an aggregate infection from multiple individual parasites. We hypothesized that although multiple ITS copies are present within a parasite spore, the DNA sequences of these copies are identical, and thus individual C. shasta spores are a single genotype. We tested this by extracting and sequencing DNA from individual myxospores. We trialed three approaches for in-tube DNA extraction; digestion with proteinase K was superior to simply rehydrating spores, or incubation in the buffer. Sequences from 14 myxospores were each a mixture of genotypes II and III. Therefore, intra-genomic ribosomal DNA variants exist within individual parasite spores, and II and III should no longer be regarded as discrete C. shasta genotypes. This single-spore genotyping approach will be a useful tool for testing validity of other C. shasta genotypes, and for correctly matching genotype with phenotype for mixed infections of other myxozoan species.

Diagnosis and treatment of multi-species fish mortality attributed to Enteromyxum leei while in quarantine at a US aquarium.

Enteromyxum leei is an enteric myxozoan parasite of fish. This myxozoan has low host specificity and is the causative agent of myxozoan emaciation disease, known for heavy mortalities and significant financial losses within Mediterranean, Red Sea, and Asian aquaculture industries. The disease has rarely been documented within public aquaria and, to our knowledge, has never been confirmed within the USA. This case report describes an outbreak of E. leei in a population of mixed-species east African/Indo-Pacific marine fish undergoing quarantine at a public aquarium within the USA. Four of 16 different species of fish in the population, each of a different taxonomic family, were confirmed infected by the myxozoan through cloacal flush or intestinal wet mount cytology at necropsy. Clinical and histopathological findings in this case are similar to previous findings describing myxozoan emaciation disease, e.g. severe emaciation, cachexia, enteritis, and death. Sequence analysis of the 18S rDNA of intestinal samples from a powder blue tang Acanthurus leucosternon and an emperor angelfish Pomacanthus imperator confirmed the parasite to have 99-100% identity with other E. leei sequences. Spore morphology and ultrastructure were consistent with previous reports of E. leei. Treatment of clinically affected fish by oral administration of the coccidiostats amprolium and salinomycin led to reduction of mortalities and resolution of clinical signs. This case report highlights the importance of thorough examination and surveillance of fish during quarantine, particularly with respect to enteric myxozoans.

Spatial and temporal variability of myxozoan parasite, Myxobolus inornatus, prevalence in young of the year smallmouth bass in the Susquehanna River Basin, Pennsylvania.

A myxozoan parasite, Myxobolus inornatus, is one disease agent identified in young of the year (YOY) smallmouth bass in the Susquehanna River Basin, Pennsylvania. We investigated spatial and temporal variability in M. Inornatus prevalence across the Susquehanna River Basin and at several out-of-basin sites. We examined potential land use drivers of M. Inornatus prevalence including agricultural and developed land use. In 1,267 YOY smallmouth bass collected from 32 sites during 2013-2016, M. Inornatus was documented in 43.6% of samples. Among-site variability in parasite prevalence was greater than among-year variability. The effect of agricultural land use on M. Inornatus prevalence had a high probability of being positively correlated at multiple spatial scales (probability of positive effect > 0.80). The effect of developed land use on M. Inornatus prevalence had a relatively high probability of being negatively correlated at multiple spatial scales (probability of negative effect > 0.70). Our results suggest that land use practices could be related to M. Inornatus infection of smallmouth bass. Further study will be necessary to determine whether disease dynamics are a consequence of effects on the host, alterations of instream habitat mediating invertebrate host dynamics and/or survival and dispersal of the parasite infective stage.

Telomere length and antioxidant defense associate with parasite-induced retarded growth in wild brown trout.

Early growth conditions can have profound impacts on individuals' development, growth and physiology, with subsequent long-term consequences for individuals' fitness and life expectancy. Telomere length (TL) has been suggested to indicate both individual fitness and life expectancy in wide range of species, as the telomere attrition rate at early age can be accelerated due to exposure to various stressors, including parasites and inflammatory diseases, which increase production of reactive oxygen species (ROS) and influence antioxidant (AO) levels. We investigated impacts of Tetracapsuloides bryosalmonae infection, a causative agent of proliferative kidney disease (PKD), on AO status and TL in a natural population of juvenile brown trout (Salmo trutta). The fish with higher parasite load showed more severe kidney hyperplasia, anemia and smaller body size compared to less parasitized fish. Furthermore, fish with severe PKD symptoms had lower SOD-, CAT- and GST activity than fish with milder kidney hyperplasia. However, parasite load was not directly correlated either with AOs or with TL. Smaller fish showed shorter TLs, potentially reflecting lower individual quality. The fish, which were less sensitive to parasite-induced impaired growth, quantified as parasite load-adjusted fork length, showed also longer TLs, lower GR- and GST activity and less GSHtot compared to more sensitive fish. These results provide novel knowledge about the impacts of the PKD in brown trout at the molecular level and support the idea that TL may reflect individual quality and ability to cope with parasitic infections.

Conditional persistence and tolerance characterize endoparasite-colonial host interactions.

Colonial hosts offer unique opportunities for exploitation by endoparasites resulting from extensive clonal propagation, but these interactions are poorly understood. The freshwater bryozoan, Fredericella sultana, and the myxozoan, Tetracapsuloides bryosalmonae, present an appropriate model system for examining such interactions. F. sultana propagates mainly asexually, through colony fragmentation and dormant propagules (statoblasts). Our study examines how T. bryosalmonae exploits the multiple transmission routes offered by the propagation of F. sultana, evaluates the effects of such transmission on its bryozoan host, and tests the hypothesis that poor host condition provokes T. bryosalmonae to bail out of a resource that may soon be unsustainable, demonstrating terminal investment. We show that infections are present in substantial proportions of colony fragments and statoblasts over space and time and that moderate infection levels promote statoblast hatching and hence effective fecundity. We also found evidence for terminal investment, with host starvation inducing the development of transmission stages. Our results contribute to a growing picture that interactions of T. bryosalmonae and F. sultana are generally characterized by parasite persistence, facilitated by multiple transmission pathways and host condition-dependent developmental cycling, and host tolerance, promoted by effective fecundity effects and an inherent capacity for renewed growth and clonal replication.

Studies on histopathological alteration of three major organs of the goldfish, Carassius auratus L., of India due to myxozoan infection with special reference to scanning electron microscopic observation.

Severe infections by the protozoan parasite belonging to the genera Myxozoa are causing serious problems in ornamental fish reared in breeding farms. Histopathological study is being used for diagnosis of the severity of diseases. Myxozoan infections result in large scale histopathological damages in different fish tissues. No information is available regarding the histopathological changes of goldfish due to infection with myxozoans. The present study deals with the histopathological changes of the gill, fin, and skin of goldfish, infected with myxozoan parasites along with an ultrastructural study using scanning electron microscope. Several histological alterations have been observed in goldfish, like tissue damage, epithelial hyperplasia, necrosis, anoxia, localized lymphocytic infiltration, excess mucus, cellular necrosis, and epithelial proliferation. The present study revealed the invasion intensified by the occurrence of morphological lesions in the gill, skin, and fin exposed to Myxosporidia, which may lead to respiratory insufficiency in fish and even cause mass mortality.

Sinuolinea niloticus n. sp., a myxozoan parasite that causes disease in Nile tilapia (Oreochromis niloticus).

Sinuolinea species are myxozoans of the order Bivalvulida, suborder Variisporina, and family Sinuolineidae, which can be parasites for freshwater and marine fish. The aim of this study was to describe the occurrence of Sinuolinea niloticus n. sp. infecting Nile tilapia (Oreochromis niloticus) from aquaculture and from river sources with morphological and molecular analyses. Between March 2010 and November 2012, 116 Nile tilapia were randomly sampled from aquaculture net fishing (n = 56) in Mira Estrela, São Paulo, and from the Capivari River (n = 60) in Botucatu, São Paulo. The fishes that were sampled were examined by necropsy, microscopic observation and molecular techniques for detection and identification of the myxozoan causing disease in tilapia. All of the tissues that were sampled for analysis showed the presence of the parasite. It was observed by microscopy that the myxozoan belongs to the Sinuolinea genus. This identification was performed based on morphological characteristics and histopathology findings, such as structures consistent with myxozoan in the interstices in all analysed tissues, coagulative necrosis, haemorrhage, inflammatory processes, presence of melano-macrophages and eosinophils. The results of the molecular analyses revealed that the myxozoan detected and identified in this study is sister to a group of other Sinuolinea species. Because this is the first report of this parasite in Nile tilapia, the parasite was named S. niloticus n. sp. This is the first report of a Sinuolinea species in Brazil and in tilapia.