The spotted seatrout, Cynoscion nebulosus, is a popular game fish in the southeastern USA. It is estimated that nearly 90% of the adult population in South Carolina estuaries are infected in their skeletal muscle by the myxosporean, Kudoa inornata. However, little is known about this parasite\'s biology, including the distribution and densities of myxospores within tissues of infected fish, which we expect affect the physiology of their hosts. In order to correlate densities with physiological parameters in future studies, we quantified the myxospores density in muscle and characterized the variation among individual fish. Naïve juvenile seatrout was experimentally infected via presumed K. inornata actinospores exposure to raw seawater. A plug of muscle was extracted from two bilaterally symmetrical regions in the epaxial fillet from fresh and frozen carcasses. Variation in density data was calculated both within and among individuals. Within individuals, density counts were compared between left- and right-side biopsies. There was no significant difference between fresh and frozen plugs, and variation among individuals accounted for the greatest proportion of variation at 68.8%, while variation within individuals was substantial at 25.6%. Simulation and correlation tests confirmed that bilaterally symmetrical replicates varied significantly within individuals. When sampled from areas surrounding the initial biopsies, myxospore density estimates were more similar than between sides. Our findings have important implications for sampling design, particularly for studies investigating physiological parameters at the cellular or molecular level in association with parasite infection.

There is a claimed increase in the global prevalence and incidence of emerging diseases observed in many organisms. Myxozoa represents an essential group of metazoan parasites that hold both economic and ecological significance. In the current study, 1% of the fish population at two commercial goldfish (Carassius auratus) farms in Tehran and Ghom province, Iran, developed cavitating muscular lesions resembling humps in February 2021 and January 2022. Fish displaying pathological abnormalities were transported to the Ornamental Fish Clinic and subjected to clinical examination. Light microscopy was subsequently used to examine wet smears of skin and gills, as well as whitish exudate. In addition, tissue homogenates were collected for more precise identification and molecular confirmation. The study discovered that individuals from the goldfish farms were infected with the pathogenic myxozoan Myxobolus lentisuturalis, which caused significant damage to the epaxial muscles. The spores collected from the humps had a lack of uniformity and were primarily ellipsoidal in shape. Histopathological analysis also revealed parasites in various stages of development, such as plasmodia and spores, as well as inflammatory cell infiltration (macrophage, giant cell and lymphoplasmacytic infiltration) between skeletal muscle fibers. Phylogenetic analysis of M. lentisuturalis was performed by using MEGA 11 and the maximum likelihood method. M. lentisuturalis is a myxozoan parasite that has been sparsely recorded and lacks widespread recognition. The current study is the first clinical, histopathological, and molecular characterization of M. lentisuturalis isolated from the skeletal musculature of goldfish (C. auratus) in Iran.

Myxidium rhodei Léger, 1905 (Cnidaria: Myxozoa) is a kidney-infecting myxosporean that was originally described from the European bitterling Rhodeus amarus. Subsequently, it has been documented based on spore morphology in more than 40 other cypriniform species, with the roach Rutilus rutilus being the most commonly reported host. This study introduces the first comprehensive data assessment of M. rhodei, conducted through morphological, ecological and molecular methods. The morphological and phylogenetic analyses of SSU rDNA sequences of Myxidium isolates obtained from European bitterling and roach did not support parasite conspecificity from these fish. In fact, the roach-infecting isolates represent three distinct parasite species. The first two, M. rutili n. sp. and M. rutilusi n. sp., are closely related cryptic species clustering with other myxosporeans in the freshwater urinary clade, sharing the same tissue tropism. The third one, M. batuevae n. sp., previously assigned to M. cf. rhodei, clustered in the hepatic biliary clade sister to bitterling-infecting M. rhodei. Our examination of diverse cypriniform fishes, coupled with molecular and morphological analyses, allowed us to untangle the cryptic species nature of M. rhodei and discover the existence of novel species. This underscores the largely undiscovered range of myxozoan diversity and highlights the need to incorporate sequence data in diagnosing novel species.
UNASSIGNED: Résoudre le casse-tête de Myxidium rhodei (Myxozoa) : aperçu de sa phylogénie et de sa spécificité d’hôte chez les Cypriniformes.
UNASSIGNED: Myxidium rhodei Léger, 1905 (Cnidaria : Myxozoa) est un Myxosporea infectant les reins qui a été décrit à l’origine chez la bouvière, Rhodeus amarus. Par la suite, il a été documenté, sur la base de la morphologie des spores, chez plus de 40 autres espèces de cypriniformes, le gardon Rutilus rutilus étant l’hôte le plus fréquemment signalé. Cette étude présente la première évaluation complète des données sur M. rhodei, réalisée par des méthodes morphologiques, écologiques et moléculaires. Les analyse morphologiques et phylogénétiques des séquences d’ADNr SSU des isolats de Myxidium obtenus à partir de bouvières et de gardons européens n’ont pas confirmé la conspécificité du parasite de ces poissons. En fait, les isolats infectant les gardons représentent trois espèces distinctes de parasites. Les deux premières, M. rutili n. sp. et M. rutilusi n. sp., sont des espèces cryptiques étroitement apparentées, regroupées avec d’autres Myxosporea du clade urinaire d’eau douce, partageant le même tropisme tissulaire. La troisième, M. batuevae n. sp., précédemment attribuée à M. cf. rhodei, appartient au clade biliaire hépatique, groupe-frère de M. rhodei infectant la bouvière. Notre examen de divers poissons cypriniformes, couplé à des analyses moléculaires et morphologiques, nous a permis de démêler la nature cryptique des espèces de M. rhodei et de découvrir l’existence de nouvelles espèces. Cela souligne la diversité largement méconnue des Myxozoaires et souligne la nécessité d’incorporer des données de séquence dans le diagnostic de nouvelles espèces.

Myxozoa, a unique group of obligate endoparasites within the phylum Cnidaria, can cause emerging diseases in wild and cultured fish populations. Recently, the myxozoan Myxobolus bejeranoi has been identified as a prevalent pathogen infecting the gills of cultured hybrid tilapia, leading to systemic immune suppression and considerable mortality. Here, we employed a proteomic approach to examine the impact of M. bejeranoi infection on fish gills, focusing on the structure of the granulomata, or cyst, formed around the proliferating parasite to prevent its spread to surrounding tissue. Enrichment analysis showed increased immune response and oxidative stress in infected gill tissue, most markedly in the cyst\'s wall. The intense immune reaction included a consortium of endopeptidase inhibitors, potentially combating the myxozoan arsenal of secreted proteases. Analysis of the cyst\'s proteome and histology staining indicated that keratin intermediate filaments contribute to its structural rigidity. Moreover, we uncovered skin-specific proteins, including a grainyhead-like transcription factor and a teleost-specific S100 calcium-binding protein that may play a role in epithelial morphogenesis and cysts formation. These findings deepen our understanding of the proteomic elements that grant the cyst its distinctive nature at the critical interface between the fish host and myxozoan parasite.

The thermotactic response of brown trout (Salmo trutta) was examined with the goal to investigate potential effects of the emerging temperature-dependent fatal trout disease PKD (proliferative kidney disease). First the differences in cold-water preferences of two forms of brown trout, lacustrine (migratory) and riverine, were determined. Second, it was studied whether this preference was changed in fish infected with PKD. The experiment involved a one-week habituation period at 14 °C in a two-chamber runway followed by a week of 3 °C temperature difference between the two runways. The fish could freely move between lanes via an opening at the end where food was provided. The temperature manipulation was repeated twice, and there were 3 trials per experimental group. All fish developed a clear spatial preference in the test. Lacustrine trout demonstrated a preference for warmer water, while riverine trout preferred cooler water. This may increase the risk to PKD in the lacustrine form. Most strikingly, riverine trout experimentally exposed to Tetracapsuloides bryosalmonae, the parasite that causes PKD, demonstrated stronger cold-seeking behaviour than control fish. Cold seeking behaviour suggests the occurrence of a disease-induced behavioural chill response, which may play an important role in disease recovery. This demonstrates the significance of protecting river connectivity and cold-water sanctuaries as management strategies for preserving salmonid populations in a warming climate.

BACKGROUND: Our investigation focused into Labeo rohita, commonly known as Rui, a freshwater aquatic species in Bangladesh. Despite their nutritional significance, these fish faced a pressing challenge: parasite infections threaten the economic stability of the aquaculture sector.
OBJECTIVE: The present study aimed to investigate the parasite and histological changes in major organs of L. rohita, collected from Khulna region - Dumuria, Paikgacha and Rupsha.
METHODS: About 180 (30/month) specimens were collected between the month of March and August 2023 to observe the parasitic status in L. rohita.
RESULTS: Through microscopic examination, a total of 323 parasites were uncovered, spanning categories including Cestode, Nematode, Acanthocephala, Trematode and Digenia, predominantly residing in the intestines of L. rohita. The highest prevalence rate (70%) was recorded in both March and May 2023, with peak mean intensity observed in July (3.73). Notably, the highest mean abundance (2.37) exhibited in July and index of infestation (45.34) in June. Histological analysis confirmed parasitic infestations in the gastrointestinal region, with displaying histological changes within major organs such as the liver, kidney, gills, spleen and testicles due to parasitic infection.
CONCLUSIONS: This study concluded that the indentified six categories of parasite and the affect of parasitic infestation in major organs of L. rohita within the study period. Urgent efforts to implement effective strategies for controlling the parasite infections in aquaculture to ensure the sustainable production of this invaluable fish species.

Nile tilapia (Oreochromis niloticus) is valued in aquaculture because of its quick development and ability to thrive in various environments. Myxosporeans are among the fish parasites that affect fish productivity, as they impact fish growth and reproduction, resulting in large fish deaths in farms and hatcheries. This study has been focused on morpho-molecular identification for the myxosporean parasites infecting Nile tilapia from three governorates in Egypt and assessment of gene expression of different cytokines (Interleukin-1βeta (IL-1β), major histocompatibility complex class II (MHC-II), and clusters of differentiation 4 (CD-4) and 8 (CD-8)) in tissues. Additionally, this work aimed to correlate the developed histopathological alterations and inflammatory reactions in gills with immunohistochemical expression of inducible nitric oxide synthase (iNOS) and tumor necrosis factor-alpha (TNF-α). Finally, the infected fish\'s cortisol levels and blood glucose were assessed. Results of BLAST sequence analysis of the 18S rRNA for the collected protozoans confirmed Myxobolus agolus, M. brachysporus, M. tilapiae, and Henneguya species. The molecular characterization of the immunological status of gills revealed marked upregulation of different inflammatory cytokines in the gills of infected fish. There was a significantly increased serum cortisol and glucose level in infected fish compared with control, non-infected ones. Severe histopathological alterations were observed in the infected fish gills, associated with increased expression of iNOS and TNF-α and related to myxosporean infection. The present study provides new insights into oxidative stress biomarkers in Nile tilapia infected with Myxosporeans and elucidates the gill\'s immune status changes as a portal of entry for protozoa that contribute to tissue damage.

UNASSIGNED: Little is known about the proteomic changes at the portals of entry in rainbow trout after infection with the myxozoan parasites, Myxobolus cerebralis, and Tetracapsuloides bryosalmonae. Whirling disease (WD) is a severe disease of salmonids, caused by the myxosporean M. cerebralis, while, proliferative kidney disease (PKD) is caused by T. bryosalmonae, which instead belongs to the class Malacosporea. Climate change is providing more suitable conditions for myxozoan parasites lifecycle, posing a high risk to salmonid aquaculture and contributing to the decline of wild trout populations in North America and Europe. Therefore, the aim of this study was to provide the first proteomic profiles of the host in the search for evasion strategies during single and coinfection with M. cerebralis and T. bryosalmonae.
UNASSIGNED: One group of fish was initially infected with M. cerebralis and another group with T. bryosalmonae. After 30 days, half of the fish in each group were co-infected with the other parasite. Using a quantitative proteomic approach, we investigated proteomic changes in the caudal fins and gills of rainbow trout before and after co-infection.
UNASSIGNED: In the caudal fins, 16 proteins were differentially regulated post exposure to M. cerebralis, whereas 27 proteins were differentially modulated in the gills of the infected rainbow trout post exposure to T. bryosalmonae. After co-infection, 4 proteins involved in parasite recognition and the regulation of host immune responses were differentially modulated between the groups in the caudal fin. In the gills, 11 proteins involved in parasite recognition and host immunity, including 4 myxozoan proteins predicted to be virulence factors, were differentially modulated.
UNASSIGNED: The results of this study increase our knowledge on rainbow trout co-infections by myxozoan parasites and rainbow trout immune responses against myxozoans at the portals of entry, supporting a better understanding of these host-parasite interactions.

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.

Members of the genus Ortholinea are among the worldwide distributed myxozoan parasites that mainly infect marine fish. In this study, a new myxosporean species, Ortholinea hamsiensis n. sp., was isolated from the urinary bladder of European anchovy Engraulis engrasicolus collected from the Sinop coasts of the Black Sea. The prevalence and density values of infection were 1.4% and 1–5 individuals in the field of view (1 + ), respectively. Mature myxospores are subspherical with slight tapering down to the less pronounced tip in the frontal view and subspherical in the sutural view. Myxospores measured 9.1 ± 0.25 (8.8–9.9) μm in length, 9.2 ± 0.11 (8.9–9.4) μm in thickness, and 8.4 ± 0.33 (8.2-9.1) μm in width. Two polar capsules equal in size measured 3.1 ± 0.11 (3.0–3.3) μm in length and 2.7 ± 0.11 (2.6–2.9) μm in width. The polar tubule had 3–4 coils. Along with morphological peculiarities, the results of the 18S rDNA also revealed it to be a new species for science compared to the other species of the genus. In this study, another myxosporean species O. gobiusi was also detected in round goby Neogobius melanostomus with a prevalence of infection value of 4.8% and a density of 1–5 individuals in the field of view (1 + ). The present study also provided the first data of 18S rDNA of O. gobiusi from N. melanostomus and type species of the genus O. divergens from Gobius niger and the phylogenetic relationships of these species with other Ortholinea species have been revealed.