Molecular and SEM studies on Thaparocleidus vistulensis (Siwak, 1932) (Monopisthocotyla, Ancylodiscoididae)

Presenting new molecular and scanning electron microscope (SEM) features, this study gives additional data to the better knowledge of Thaparocleidus vistulensis (Siwak, 1932) (Monopisthocotyla, Ancylodiscoididae), a parasite of the European catfish Silurus glanis Linnaeus, 1758 (Siluriformes, Siluridae) cultured in a commercial fish farm in Hungary. In addition, notes on the early development of sclerotized anchors are also provided. The main morphological difference of T. vistulensis compared to other congeneric species is associated with the male copulatory organ, which exhibits 5-7 loops in the middle of the penis length and a long open V-shaped sclerotized accessory piece, dividing terminally into two parts, securing the terminal part of the penis tube. The present study provides for the first time molecular characterization data based on the 2694 bp long nucleotide sequence of rDNA (ITS1, 5.8S, ITS2, and flanked with partial 18S and partial 28S) submitted in GenBank with the accession number OR916383. A phylogenetic tree based on ITS1 sequences supports a well-defined clade including T. vistulensis, forming a sister group with T. siluri, a species-specific monopisthocotylan parasite to S. glanis. The morphological characterization of T. vistulensis, especially for the male copulatory organ, together with the molecular data in the present study, extends knowledge about this monopisthocotylan species and provides new information for future phylogeny studies.

Morphological and molecular characterisation of two closely related species: Myxobolus tihanyensis n. sp. and Myxobolus sandrae Reuss, 1906

Based on spore morphology and small subunit ribosomal DNA sequences, we describe a new Myxobolus species, Myxobolus tihanyensis n. sp., parasitizing the European perch (Perca fluviatilis) from Lake Balaton in Hungary. The brownish plasmodia were found in various locations of the body, mainly in the muscle adjacent with fins and vertebrae. The spores were ovoid, and measured 9.84 ± 0.38 μm in length, 7.69 ± 0.23 μm in width, and 5.35 ± 0.21 μm in thickness, with 8-10 sutural (edge) markings. The polar capsules were mostly equal in size, with 4.91 ± 0.39 μm in length and 2.27 ± 0.24 μm in width. The polar tubule length is 38.15 μm ± 2.70, and coiled 6-7 times. In particular, these morphological data overlap with those of Myxobolus sandrae Reuss1906 infecting the European perch (Perca fluviatilis), the pikeperch (Sander lucioperca), and the Volga pikeperch (Sander volgensis) according to previous descriptions and the taxonomic data here described. However, the phylogenetic analyses separate the two species as sister clades with 16.8% genetic distance. This study has demonstrated that the two species of Myxobolus exhibit phenotypic similarity while displaying significant genetic divergence. Therefore, the importance of including molecular data in the taxonomic description of myxozoans is emphasized.

Morphology and phylogeny of Coccomyxa bragantinensis n. sp. (Cnidaria: Myxozoa) found parasitising the Coco Sea catfish, Bagre bagre (Siluriformes: Ariidae), captured off the coast of Northern Brazil

The present study describes Coccomyxa bragantinensis n. sp., which was found parasitising the gallbladder of the Coco Sea catfish, Bagre bagre, captured off Ajuruteua beach, in the region of Bragança in Pará state, northern Brazil. Most (77.5%) of the 40 fish specimens examined (31/40) had myxospores floating in the bile liquid. These spores are partially ellipsoid, with a tapering anterior extremity and a rounded, elongated posterior extremity with a single piriform polar capsule containing a helicoidal polar filament, with 5-6 coils. A partial sequence of 957 bp of the SSU rDNA gene was obtained from the specimens and deposited in GenBank (xxx). The new species described here - Coccomyxa bragantinensis n. sp. - is phylogenetically similar to Coccomyxa morovi, although it differs from all the other Coccomyxa species and is the first species of this genus to be described from Brazil on the basis of molecular evidence.

Reproductive strategies of the parasitic flatworm Thaparocleidus vistulensis (Siwak, 1932) (platyhelminthes, monogenea) infecting the European catfish Silurus glanis Linnaeus, 1758

The life cycle of Thaparocleidus vistulensis (Siwak, 1932), a host-specific monogenean parasite of European catfish (Silurus glanis Linnaeus, 1758), was investigated by detailed observation of infection dynamics, egg development, hatching rate and in vitro survival rates of the parasite at different life stages at 23 °C. A total of 30 naive fingerlings were infected in three exposure trials by co-habitation with donor fish carrying adult parasites. Two fish were dissected every two days during the 10-day experimental period to explore the development of larvae and juvenile parasites on the host gills. Freshly laid eggs by adult monogeneans were collected and observed daily under a light microscope until hatching. A total of 445 eggs were collected and distributed into wells of 96-well microtiter plates containing filtered fish tank water to determine their hatching rates. A similar method was used to investigate the survival rates of isolated parasites at different developmental stages (larvae, juveniles, and adults). T. vistulensis populations on the European catfish in fish tanks increased markedly within ten days, dependent on the severity of the initial infection levels of the donor fish. The first eggs hatched three to four days after oviposition, and the hatching rate peaked on the fifth day (89.7%). The survival rate for freely swimming oncomiracidia without host was 7.4% after five days, whereas isolated juvenile and adult parasites showed a higher dependence of host contact (survival rates three days post-isolation of 0.9% and 1.6%, respectively). The data allows prediction of parasite-host dynamics and may improve control of gill-disease in cultured European catfish stocks in fish farms.

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.

Molecular evidence of the absence of Metagonimus yokogawai (Katsurada, 1912) in Europe: report of Metagonimus sp. in cyprinoid fish from the River Danube in Hungary

Trematodes of the genus Metagonimus Katsurada, 1912 (Digenea: Heterophyidae) are zoonotic parasites that cause infections in humans, with most cases reported in Southeast Asia. Larvae from the second intermediate host, called metacercariae, of one of human-infecting species, M. yokogawai (Katsurada, 1912), have been reported from cyprinoid fish in Europe. In the present study, we provided DNA-based evidence that metacercariae of Metagonimus, which are commonly found in the scales of various cyprinoids in Central Europe (Danube River in Hungary) do not belong to M. yokogawai. Sequence analysis of the ITS region, 28S rDNA, and cox1 genes showed that this species is clearly distinct from all Asian species, including M. yokogawai, which probably does not occur in Europe. Metacercariae from cyprinoids might belong to Metagonimus romanicus (Ciurea, 1915), an insufficiently known species described from Romania.

Effect of 80% ethanol or 10% formalin fixation, freezing at −20 °C and staining on Myxobolus (Myxosporea) spores to be deposited in parasitological collections

The preparation of myxosporeans for the description of myxospores and their preservation as type material in parasitological collections show great variations. Most frequently, formalin and ethanol are used for fixation and Giemsa solution for staining spores. In this work, authors studied the effect of 80% ethanol and 10% formalin fixation, freezing at −20 °C and staining on the size and transparency of two Myxobolus species of cyprinid fishes, M. bramae and M. bliccae spore, and recommended a new method for the deposition of type material to parasitological collections in museums. The studies have commended that fresh spores from mature plasmodia are the best material for measuring the size and studying the inner structures, the number of polar tubules in polar capsules and the morphological characters of the intercapsular appendix. The obtained quantitative data suggest that cryo- and chemical preservation do not have a notable negative effect on spores compared to fresh samples but they decrease the transparency of spores. Staining the spores with Ziehl–Neelsen has proved to be a useful method for studying the fine structure without size reduction, while Giemsa staining induced a shrinkage of spores so it seems to be not ideal for description of a new species. When treating spores of Myxobolus spp. with Lugol's solution, iodinophilous vacuoles in the sporoplasm were not recognised but visualisation of the coils of polar tubules was enhanced. As a type material for newly described species, authors suggest phototypes and spores fixed in 80% ethanol to be deposited into collections, as this preservation method is suitable for subsequent research, such as re-measurements and molecular analysis.

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The effect of fixation, freezing at −20 C and staining on myxospores was studied.

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Model materials were myxospores of Myxobolus bramae and M. bliccae.

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No changes in size were observed on frozen at −20 C and 80% ethanol- or 10% formalin-fixed spores.

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A shrinkage of spores was noticed when staining spores with Giemsa solution.

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Phototypes and 80% ethanol-fixed spores are recommended for collections as type material.

Morphological and molecular studies on two myxosporean infections of cyprinid fishes: Thelohanellus pyriformis from tench and Thelohanellus cf. fuhrmanni from nase

During surveys on myxosporean parasites of Lake Balaton and River Danube fishes, two Thelohanellus spp. were found on tench (Tinca tinca) and on common nase (Chondrostoma nasus). They were identified as Thelohanellus pyriformis and Thelohanellus cf. fuhrmanni, respectively. Myxospores of T. pyriformis from tench were collected from arteria branchialis afferens of gill filaments. The mature myxospores of this species were pyriform in shape and 19 ± 0.6l (18–19.5) long, 8.2 ± 0.54 (7.5–9) wide, 7.3 ± 0.25 (7–7.5) thick containing polar tubules with 9–10 turns. The plasmodia of Thelohanellus cf. fuhrmanni were collected from under the skin of snout of the common nase. The myxospores were pyriform, 16.3 ± 0.39l (15.5–16.5) long, 6.5 ± 0.55 (6.3–7) wide, 6.3 ± 0.53 (5.8–7) thick containing polar tubules with 6 turns. Small subunit ribosomal DNA sequences of both Thelohanellus species differed from other known myxozoans. The myxospores morphology, histopathology and ssrDNA sequences supported a diagnosis of T. pyriformis from tench and T. cf. fuhrmanni from common nase.

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Two Thelohanellus spp. were redescribed from cyprinid fishes.

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Thelohanellus pyriformis was recorded and described from the type host tench (Tinca tinca).

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Thelohanellus cf. fuhrmanni was found in an atypical host, common nase (Chondrostoma nasus).

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The morphology of both Thelohanellus species was supported by histology and ssrDNA sequence data.

Extreme pathological symptom generated by Dermocystidium koi infection of common carp (Cyprinus carpio L.) in Hungary

Dermocystidiosis in common carp (Cyprinus carpio L.) as a skin infection in the form of small, pea-sized bulging nodules is well-known in Hungary. Its occurrence is sporadic, and the pathogenic effect is generally moderate. Nonetheless, here we report an unusual case of the infection when a mass of dermocystid spore-filled hyphae-like cysts formed a large tumour-like nodule under the skin intruding deeply in the red muscle on one side occipital region of the fish body. Histological sections showed that the tumour-like nodule was composed of two layers, a pale peripheral part with a high mass of cysts surrounded by some cell debris of muscle cells and a dark central part with a less dense meshwork of tubular cysts which were embedded in the partially damaged red muscle tissue. No infection was found in the white muscle. Sequences of 18S rDNA of spores from the tumour-like nodule showed a complete identity to sequences from typical bulging nodules in skin. They were also highly similar to the sequences of D. anguillae clones (99.5%-99.4%), to some samples of D. salmonis (99.7% and 99.4%), and to the Dermocystidium sp. CM-2002 (99.4%) from European perch.

Viruses Infecting the European Catfish (Silurus glanis)

In aquaculture, disease management and pathogen control are key for a successful fish farming industry. In past years, European catfish farming has been flourishing. However, devastating fish pathogens including limiting fish viruses are considered a big threat to further expanding of the industry. Even though mainly the ranavirus (Iridoviridea) and circovirus (Circoviridea) infections are considered well- described in European catfish, more other agents including herpes-, rhabdo or papillomaviruses are also observed in the tissues of catfish with or without any symptoms. The etiological role of these viruses has been unclear until now. Hence, there is a requisite for more detailed information about the latter and the development of preventive and therapeutic approaches to complete them. In this review, we summarize recent knowledge about viruses that affect the European catfish and describe their origin, distribution, molecular characterisation, and phylogenetic classification. We also highlight the knowledge gaps, which need more in-depth investigations in the future.

The occurrence of known Myxobolus and Thelohanellus species (Myxozoa, Myxosporea) from Indian major carps with the description of Myxobolus bandyopadhyayi n. sp. in West Bengal

Myxosporean infection of Indian major carps (rohu, Labeo rohita; catla, Gibelion catla; mrigal, Cirrhinus mrigala) was examined from two fish farms and two fish markets in West Bengal, India. One Thelohanellus and four Myxobolus species were detected from the fins and scales of the investigated species. Comprehensive morphological and molecular biological studies revealed four already known species, Thelohanellus caudatus from the fins of rohu, Myxobolus dermiscalis from the scales of rohu, Myxobolus chakravartyi from the fins of catla, and Myxobolus rewensis from the fins of mrigal. This study complemented the species description of M. chakravartyi and M. rewensis with the missing molecular data. Moreover, based on morphometrics and ssrDNA sequence data, a new species was documented from the scales of rohu, and named Myxobolus bandyopadhyayi n. sp.

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Myxozoan infections were recognised from Indian major carps in West Bengal, India.

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A new Myxobolus species was discovered from the scales of rohu: Myxobolus bandiopadhyayi n. sp.

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Redescription of four known Indian Myxobolus and Thelohanellus spp.

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The first molecular data were obtained on Myxobolus chakravartyi and Myxobolus rewensis.

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ssrDNA was used to support the morphological identification of taxa.

An alien parasite affects local fauna-Confirmation of Sinergasilus major (Copepoda: Ergasilidae) switching hosts and infecting native Silurus glanis (Actinopterygii: Siluridae) in Hungary

In 2016, an intense copepod infection was recorded from a reservoir in proximity to the Danube River in Hungary from visibly emaciated wels catfish, Silurus glanis. The parasite-induced pathology was described but parasite identity was not conclusive. Additional sample collections in 2017 and 2018 allowed for identification using both light and scanning electron microscopy, alongside genetic characterisation. The copepods were confirmed to be ergasilids, Sinergasilus major, distinctly different from any previous infection on silurids in Europe. This is the first record of this parasite from Hungary and the first host record from wels catfish.

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First record of Sinergasilus major from wels catfish (Silurus glanis).

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First record of S. major from Hungary.

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Light and scanning eletron microscopy support identification of S. major.

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100% similarity of the 18S rDNA provides significant confidence to the identification of the copepods as S. major.

Evidence of the American Myxobolus dechtiari was introduced along with its host Lepomis gibbosus in Europe: Molecular and histological data

The American pumpkinseed Lepomis gibbosus, was introduced to Europe more than one hundred years ago. Currently it is a common fish in European freshwaters but relatively few specific parasites infect this fish in this new habitat. In Europe only a single species, Myxobolus dechtiari seems to represent the American myxosporean fauna of centrarchid fishes. M. dechtiari was found in both Portugal and Hungary. This species forms plasmodia with elongated shape inside the cartilaginous rays of gill filaments. In the advanced stage of infection, after disruption of plasmodia, small groups of myxospores remain enclosed in the cartilaginous gill rays causing distortions in the filaments. Myxospores were ellipsoidal in frontal view and lemon-shape in sutural, length 12.5 ± 0.46 (12–13.4) μm, width 10 ± 0.37 (9.6–10.4) μm, and thickness 7.4 ± 0.37 (7–8) μm; the polar capsules were pyriform, equal in size, length 5.6 ± 0.21 (5.3–6) μm, width 3.2 ± 0.16 (3–3.6) μm; Seven to eight polar tube coils were arranged perpendicularly to the capsule length. There was a small, round, 0.4 ± 0.1 (0.3–05) (N = 50) intercapsular appendix in the spores. The small subunit ribosomal DNA (ssrDNA) of M. dechtiari differed from other myxozoans sequenced to date. Phylogenetic analysis of the ssrDNA gene sequence placed this species in a clade including actinospores and Myxobolus species: Raabeia type1, Triactinomyxon sp., and Myxobolus osburni infecting the same host fish.

The focus of our study was to prove that the pumpkinseed, a fish originated from North-America introduced one of its myxosporean parasite to Europe. Emphasis was put on to demonstrate the unique feature of this parasite causing infection in the cartilaginous gill rays.

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American pumpkinseed fish were introduced to Europe as an ornamental fish.

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Relatively few specific parasites are reported from the pumpkinseed in Europe.

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The myxosporean Myxobolus dechtiari described originally in Canada infects the introduced host both in Hungary and Portugal.

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SsrDNA sequences of M. dechtiari from pumpkinseed fish is provided.

Mycoplasma infections in freshwater carnivorous fishes in Hungary

The abundance of mycoplasma-like microorganisms seems to be common in the intestinal tract of fish, but their occurrence in other organs can be considered pathological. Isolation of piscine mycoplasmas is essential to prove their virulence. In this study, a total of 100 specimens of nine freshwater fish species collected from natural waters and fish farms were analysed for the prevalence of mycoplasmas in different extraintestinal organs. Our results demonstrate that mycoplasmas are present in carnivorous fish (pike, wels catfish, black bullhead and pike perch) than in cyprinids more frequently. Among the surveyed organs, they colonize mainly the gills, the kidney and the livers. Although mycoplasmas could be detected in one-fifth of samples by molecular assays, the isolation of mycoplasmas belonged to the M. sualvi cluster within the hominis group of Mycoplasmataceae, but was separate from M. mobile, has been successful only from some specimens originated from wels catfish that was feasible only by special preparation steps (prefreezing, filter sterilization and incubation conditions (long culturing period, etc.). The low-efficiency of isolation trials indicates an extensive gap in our knowledge about piscine mycoplasmas, especially in the field of their nutritional requirements.

Digenean trematodes in Hungarian freshwater aquacultures

Occurrence of metacercariae of potentially zoonotic trematodes (Platyhelminthes: Digenea) in the musculature of common carp (Cyprinus carpio L. 1758) was monitored in four Hungarian aquacultures. Four geographically distinct fish farms (located in the Northwestern, Southwestern, Northeastern and Southeastern parts of Hungary) were selected for the investigation. From each farm, a total of 258 one-summer-old fingerlings were sampled and examined in the years 2016 and 2017. In addition, in 2017, we examined 60 market size specimens (30 two-summers and 30 three-summers) sampled from the most infected aquaculture in the Northeastern part of Hungary. The fish were euthanized and decapitated whereafter their musculature (fillets) was digested in a pepsin solution to isolate metacercariae from the tissue whereafter morphological and molecular analyses (PCR and sequencing of ITS region) were performed. Opisthorchiid metacercariae were not recovered but in one of the farms numerous metacercariae were detected in the musculature of carp. They were identified as cyathocotylid trematodes based on their morphological characteristics and by sequencing the ITS region. The infection levels proved to be remarkably different among the four fish farms. Carps from the Northeastern farm were infected by large numbers of cyathocotylid metacercariae, while 8 Posthodiplostomum cuticola metacercariae were detected in the Northwestern aquaculture. In the other two farms (Southwestern and Southeastern) no infection was recorded. The infected farm is located close to a protected natural wetland habitat populated by a rich fauna of aquatic birds (potential final hosts) and snails (first intermediate host) which may create a higher risk of infection in the neighbouring fish farms.

Infection of the Carpathian brook lamprey (Eudontomyzon danfordi Regan, 1911) with a dermocystid parasite in the Tisza River Basin, Hungary

The Carpathian brook lamprey (Eudontomyzon danfordi Regan, 1911) is an endemic protected species of Cephalaspidomorphi in the Carpathian Basin. No parasites have become known from these jawless vertebrates to date. Here, the authors describe an infection from a single specimen manifesting in protuberant skin cysts 7-10 mm in diameter, scattered on the body surface. Similar dermal infection was observed in 25 of the 274 lampreys recorded in the population survey. Skin cysts filled with round spore-like structures of a dermocystid parasite were found. These particles measured 8-14 µm in diameter and had an about 0.5 µm thick wall, and containing mainly a granular mass and a relatively scarce plasma. No hyphae were recorded. Despite conspicuous morphological changes in the skin, no inflammatory reactions were found. The molecular analysis of 18S rDNA showed similarity to dermocystid species of several fish species but differed from them approximately by 2%. This is the first record of a dermocystid parasite infecting a jawless vertebrate.

Description of myxosporeans (Cnidaria: Myxozoa) infecting the popular food fish Notopterus notopterus (Pisces: Notopteridae) in Malaysia and India

This study was a co-operative investigation of myxosporean infections of Notopterus notopterus, the bronze featherback, which is a popular food fish in the South Asian region. We examined fish from Lake Kenyir, Malaysia and the River Ganga, Hastinapur, Uttar Pradesh, India, and observed infections with two myxosporeans: Myxidium cf. notopterum (Myxidiidae) and Henneguya ganapatiae (Myxobolidae), respectively. These species were identified by myxospore morphology, morphometry and host tissue affinity, and the original descriptions supplemented with small-subunit ribosomal DNA sequences and phylogenetic analysis. Free myxospores of M. cf. notopterum were found in the gallbladder, and measured 14.7 ± 0.6 μm long and 6.3 ± 0.6 μm wide; host, tissue and myxospore dimensions overlapped with the type, but differed in morphological details (spore shape, valve cell ridges) and locality (Malaysia versus India). Plasmodia and spores of H. ganapatiae were observed in gills, and myxospores had a spore body 9.7 ± 0.4 μm long, 4.5 ± 0.5 μm wide; sample locality, host, tissue, spore morphology and morphometry matched the original description. Small-subunit ribosomal DNA sequences were deposited in GenBank (M. cf. notopterum MT365527, H. ganapatiae MT365528) and both differed by >7% from congeneric species. Although the pathogenicity and clinical manifestation of myxozoan in humans are poorly understood, consumption of raw fish meat with myxozoan infection was reported to be associated with diarrhea. Identification of current parasite fauna from N. notopterus is an essential first step in assessing pathogen risks to stocks of this important food fish.

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Two myxozoan species were identified in the important food fish Notopterus notopterus.

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Myxospores of Myxidium cf. notopterum and Henneguya ganapatiae were investigated.

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Although rare myxozoan species can be zoonotic M. cf. notopterum and H. ganapatiae are not known to infect humans.

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Country-specific myxozoan parasites were found in N. notopterus from India and Malaysia.

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DNA sequence data helped to clarify the taxa and improve identification.

Detection of cyprinid herpesvirus 1 (CyHV-1) in barbel (Barbus barbus): First molecular evidence for the presence of CyHV-1 in fish other than carp (Cyprinus carpio)

Two adult barbels (Barbus barbus) with visible skin tumours were subjected to histopathological and molecular examinations. The fish were caught in the River Danube near Budapest. Papillomas were found around their oral cavity, at the operculum and at the pectoral fins, while epidermal hyperplasias were seen on the body surface. Cyprinid herpesvirus 1 (CyHV-1) was detected in the kidney of the specimens by polymerase chain reaction (PCR), and barbel circovirus 1 (BaCV1) was found in all internal organs and in the tissues of the tumours. The whole genome of BaCV1 and three conserved genes from the genome of CyHV-1 were sequenced. Previously, BaCV1 had been reported only once from a mass mortality event among barbel fry. The whole genome sequence of our circovirus shared 99.9% nucleotide identity with that of the formerly reported BaCV1. CyHV-1 is known to infect common carp and coloured carp (Cyprinus carpio), and has been assumed to infect other cyprinid fish species as well. We found the nucleotide sequences of the genes of CyHV-1 to be identical in 98.7% to those of the previous isolates from carp. To the best of our knowledge, this is the first molecular confirmation of the presence of CyHV-1 DNA in cyprinid fish species other than carp.

New record of metacercariae of the North American Posthodiplostomum centrarchi (Digenea, Diplostomidae) in pumpkinseed (Lepomis gibbosus) in Hungary

Two species of the genus Posthodiplostomum (Digenea: Diplostomatidae) (Posthodiplostomum brevicaudatum Nordmann, 1832 and Posthodiplostomum cuticola Nordmann, 1832) are known as parasites of Hungarian native fishes. Metacercariae of P. cuticola are widespread in Europe and cause black spot disease. Several species of Posthodiplostomum were described also from North America but none of them has been isolated in Hungary up to now. Posthodiplostomum centrarchi Hoffman, 1958 has been detected recently in pumpkinseeds (Lepomis gibbosus L., 1758) in several European countries. Posthodiplostomum centrarchi was isolated for the first time in Hungary from pumpkinseeds caught in the Maconka water reservoir in 2015. Thereafter, several natural waters (e.g. the River Danube, Lake Balaton and the Sió channel) were sampled in order to determine its presence and distribution. Only the native species P. cuticola was detected in Lake Balaton on cyprinids but a relatively high infection rate of P. centrarchi was observed in the Sió channel close to the lake. Pathological changes were absent, and metacercariae were mostly attached to the surface of the liver, kidney and heart. The phylogenetic analysis of the ITS and COI sequences of P. centrarchi and P. cuticola clustered into two distinct branches, which was in agreement with the morphological results.

Efficacy of silver nanoparticles to control flavobacteriosis caused by Flavobacterium johnsoniae in common carp Cyprinus carpio

Flavobacterial infections are among the causes of fish losses in farms with the emergence of antibiotic-resistant isolates. Silver nanoparticles (AgNPs) are known for their potent antimicrobial activity against different types of bacteria. In this study, we evaluated the antibacterial properties of AgNPs (diameter: 23 nm) against Flavobacterium johnsoniae infection in common carp Cyprinus carpio. The assays included both in vitro and in vivo antibacterial tests in addition to evaluation of cell toxicity effects on the fish cell lines. The in vitro results revealed potent inhibitory effects of AgNPs on the growth of F. johnsoniae with a minimum inhibitory concentration of 34 µg ml-1. Fish cell (epithelioma papulosum cyprini and koi carp fin) viability was 95-100% after exposure to 500 ng ml-1 (and lower concentrations) of AgNPs. In the exposure experiment, mortality rates decreased from 45% in the infected non-treated group to 30 and 15% in the intraperitoneal injection and immersion-treated groups, respectively. Neither of the treated groups showed any clinical signs or histopathological lesions. The single-dose treatment with AgNPs during early infection with F. johnsoniae aided in minimizing fish losses.

Henneguya (Cnidaria: Myxosporea: Myxobolidae) infections of cultured barramundi, Lates calcarifer (Perciformes: Latidae) in an estuarine wetlands system of Malaysia: description of Henneguya setiuensis n. sp., Henneguya voronini n. sp. and Henneguya calcarifer n. sp

Examination of 35 barramundi (Lates calcarifer) from aquaculture cages in Setiu Wetland, Malaysia, revealed a single fish infected with three Henneguya spp. (Cnidaria: Myxosporea). Characterization of the infections using tissue tropism, myxospore morphology and morphometry and 18S rDNA sequencing supported description of three new species: Henneguya setiuensis n. sp., Henneguya voronini n. sp. and H. calcarifer n. sp. Myxospores of all three species had typical Henneguya morphology, with two polar capsules in the plane of the suture, an oval spore body, smooth valve cell surfaces, and two caudal appendages. Spores were morphometrically similar, and many dimensions overlapped, but H. voronini n. sp. had shorter caudal appendages compared with H. calcarifer n. sp. and H. setiuensis n. sp. Gross tissue tropism distinguished the muscle parasite H. calcarifer n. sp. from gill parasites H. setiuensis n. sp. and H. voronini n. sp.; and these latter two species were further separable by fine-scale location of developing plasmodia, which were intra-lamellar for H. setiuensis n. sp. and basal to the filaments for H. voronini n. sp. small subunit ribosomal DNA sequences distinguished all three species: the two gill species H. setiuensis n. sp. and H voronini n. sp. were only 88% similar (over 1708 bp), whereas the muscle species H. calcarifer n. sp. was most similar to H. voronini n. sp. (98% over 1696 bp). None of the three novel species was more than 90% similar to any known myxosporean sequence in GenBank. Low infection prevalence of these myxosporeans and lack of obvious tissue pathology from developing plasmodia suggested none of these parasites are currently a problem for barramundi culture in Setiu Wetland; however additional surveys of fish, particularly at different times of the year, would be informative for better risk assessment.

Description of Henneguya jaczoi sp. n. (myxosporea, myxobolidae) from Perca fluviatilis (L.) (pisces, percidae) with some remarks on the systematics of Henneguya spp. of european fishes

A new Henneguya species, H. jaczoi sp. n., is described from perch (Perca fluviatilis) from Lake Balaton, Hungary. This species infects the palatal region of the fish, forming large plasmodia in the thickened caudal part of the buccal cavity and at the dorsal ends of the cartilaginous gill arches. The species differs from the gill-dwelling Henneguya species of perch and pike (Esox lucius) both morphologically and in molecular aspects. The authors conclude that the type species H. psorospermica Thélohan is a specific parasite of pike, while the species forming plasmodia in the gills of perch corresponds to H. texta Cohn, which was hitherto regarded as a synonym of H. psorospermica. Besides the above-mentioned species, H. creplini was frequently found in pikeperch (Sander lucioperca) and Volga pikeperch (Sander volgensis), but no Henneguya infection has been recorded in ruffe (Gymnocephalus cernua), which is a common percid fish of the lake and is known to be the type host species for H. creplini.

Myxobolus infection in the cornea of the roach (Rutilus rutilus) in Lake Balaton

Infection of the cornea in fishes by Myxobolus plasmodia is a common but still little known site preference of myxosporeans. A sporadic but striking infection in the cornea of the roach (Rutilus rutilus) was observed in Lake Balaton, Hungary. Relatively small, round plasmodia 250 to 500 μm in diameter developed in the dense connective tissue of the cornea. Morphological and molecular biological examination of spores collected from cysts in the cornea demonstrated that this infection is caused by Myxobolus fundamentalis, a species hitherto reported only from the cartilaginous gill arch of the roach. The 18S rDNA sequences of spores from the cornea showed 99.9% identity to the sequences of spores from the gill arch, and they also shared 99.9% identity with the sequences of triactinomyxon actinospores obtained from the oligochaete Isochaetides michaelseni.

Cross section of gill filaments in histological preparations helps better identification of the location of myxosporean plasmodia in gill tissues

Location and tissue preference of filamental-type myxosporean plasmodia in histological slides of the gills can be properly identified only in cross sections of the gill filaments. The authors selected three myxosporeans (Myxobolus rutili, M. dispar and Henneguya psorospermica, parasites of the roach, the common carp and the pike, respectively) for studying the problem. The plasmodia of these species studied in longitudinal sections were earlier regarded as developing inside the filamental arteries. Cross sections of the filaments showed that all the three species developed plasmodia in the dense connective tissue constituting the adventitia of gill arteries and covering the cartilaginous gill rays. Myxobolus rutili started its development close to the afferent branchial artery but attached to the cartilaginous gill ray. More developed plasmodia of this species surrounded the rays. Plasmodia of M. dispar were formed on the inner side of the afferent branchial artery, while those of H. psorospermica were located at the external side of the efferent branchial artery.

Morphological, histological, and molecular description of Myxobolus ompok n. sp. (Myxosporea: Myxobolidae), a kidney myxozoan from Pabdah catfish Ompok pabda (Hamilton, 1822) (Siluriformes: Siluridae) in India

In a parasitological survey of freshwater fishes near Meerut, Uttar Pradesh, India, myxozoan infections in Pabdah catfish Ompok pabda Ham. (Siluriformes: Siluridae) were found. Round plasmodia and scattered spores of Myxobolus ompok n. sp. were found in the kidney of the host. Plasmodia measuring 150-200 μm were located in the renal interstitium. Spores of Myxobolus ompok n. sp. were elongated pyriform, 13.6-14.4 (14.8 ± 0.42) μm long, 5.6-6.4 (6.5 ± 0.33) μm wide, and 5.2-6.4 (5.9 ± 0.43) μm thick with two equal polar capsules measuring 8.0-8.5 (8.2 ± 0.2) μm in length and 1.5-2.4 (1.8 ± 0.33) in width having six filamental turns. Both the morphology and DNA analysis of the 18S rRNA gene revealed that Myxobolus ompok n. sp. is distinct from previously described species of Myxobolus and shares no significant similarity with any other Myxobolus deposited in the GenBank database. Phylogenetic analysis inferred that this species showed the closest similarity to Myxobolus miyarii (KT001495). This is the first record of any Myxobolus sp. from O. pabda in India.

Histopathological changes on the gills of asp (Aspius aspius) and European catfish (Silurus glanis) caused by Lamproglena pulchella and a Lamproglena sp. (Copepoda: Lernaeidae), respectively

In a parasitology survey of Hungarian fishes, heavy infections of parasitic copepods Lamproglena pulchella and a Lamproglena sp. were found in the gills of the asp and the European catfish, respectively. Individuals of both fish species were emaciated and infected with hundreds of Lamproglena. Copepods located close to the tip of gill filaments and formed a depression at the attachment sites. In histological sections, cell degenerations and local haemorrhages were present adjacent to the maxillipeds and where the maxillary claws pierced the gill tissue. Around maxillae and in the midgut of the Lamproglena, damaged piscine blood cells and remains of the gill tissue were observed. Host reaction was expressed by proliferation of epithelioid cells, increase in both number and size of goblet and mast cells and formation of giant cells.

Molecular detection and genome analysis of circoviruses of European eel (Anguilla anguilla) and sichel (Pelecus cultratus)

The prevalence and distribution of piscine circoviruses (CVs) were tested in a routine virus monitoring programme in Lake Balaton, Hungary. A high prevalence of European eel CV (EeCV) was found in the apparently healthy eel population (35.5%). The copy number of the viral DNA in different organs was determined by quantitative real-time PCR. The results suggested that some eel specimens were in active viraemic status despite their asymptomatic condition. Furthermore, a novel, previously undescribed CV was also detected in eel and sichel samples. Full genome characterisation confirmed that the virus represents a novel EeCV species (EeCV-2). The genome contains an integrated eel chromosome-derived fragment, suggesting that the original host of the virus was the eel and it probably emerged subsequently in the sichel by host switching. In some samples, an additional, 1,111-nt-long circular ssDNA was also observed involving a CV-like stem-loop structure and an ORF showing homology to CV capsid protein genes, without any sign of a replication initiator protein sequence.

Molecular biological studies of adult and metacercarial stages of Petasiger exaeretus Dietz, 1909 (Digenea: Echinostomatidae)

Molnár et al. (2015) reported two types of echinostomatid metacercariae in the lateral line organ of Hungarian fish species. Type 1 metacercariae possessed 27 collar spines and 16 uniform and three larger dorsal spines, whereas Type 2 metacercariae bore 27 collar spines and 19 equal-sized dorsal spines. In the recent work, molecular studies carried out on the ITS region and partial 28S rDNA sequences of two types of echinostomatid metacercariae and the sequences of adult stages of the species of Petasiger Dietz, 1909 collected from cormorants (Phalacrocorax carbo L.) showed that some of the Type 2 metacercariae corresponded to Petasiger exaeretus Dietz, 1909, whereas other morphologically similar metacercariae were identified as Petasiger phalacrocoracis (Yamaguti, 1939). The sequences of the Type 1 metacercariae with three larger dorsal spines could not be identified with any of the known sequences from echinostomatid trematodes.

Diverse Chlamydia-like agents associated with epitheliocystis infection in two cyprinid fish species, the common carp (Cyprinus carpio L.) and the gibel carp (Carassius auratus gibelio L.)

During a general annual fish health survey in natural waters and ponds, epitheliocystis infections were recorded in fingerlings of two cyprinid fish species, the cultured common carp and the wild gibel carp. Benign and heavy infections were equally observed without mortality. In addition to the general health inspection of fish, histopathological examinations of infected gills and molecular biological investigations of separated epitheliocysts were performed. Epitheliocysts were formed both in the interlamellar epithelial cells and in the lamella-free multilayered epithelium of the gill filaments. At the early stage of infection darkstaining inclusion bodies densely stuffed with some pathogenic agents were located at the centre of the cell, while in a progressive stage of the process inclusion bodies within the host cells were disseminated in the cytoplasm and stained pale. Molecular studies demonstrated three different agents related to Neochlamydia, Protochlamydia and Piscichlamydia based on sequence analysis of short regions of the 16S rRNA gene. Among them, Piscichlamydia is a primary fish pathogen, while Neochlamydia and Protochlamydia mostly infect free-living amoebae but have adapted thoroughly to fish.

Malformations of the gill filaments of the ruffe Gymnocephalus cernuus (L.) (Pisces) caused by echinostomatid metacercariae

In parasite surveys of fishes from Lake Balaton and its tributaries in Hungary, infections with metacercariae of a species of the digenean genus Echinochasmus (Trematoda: Echinostomatidae) were found in seven species of fish. In ruffe, Gymnocephalus cernuus, malformations of the gill filaments apparently caused by these infections were observed. These malformations were in the form of bifurcations of the filaments at about their mid-length. At the point where the filaments bifurcate, an Echinochasmus metacercaria was always embedded in the cartilaginous ray of the gill filament. All specimens of the ruffe were found to be infected by these metacercariae, and each ruffe specimen was infected by 30-300 metacercariae. Such a bifurcation was found in all of the ruffe specimens, but, apart from these gill malformations, the metacercariae produced only local changes in the cartilage. In the other six infected fish species, only local signs were observed in the cartilage. Experimental infections of chicks with metacercariae resulted in the finding of the sexual adult (marita) of an unidentified species of Echinochasmus. ITS sequences of the adult and metacercaria corresponded with each other, and also with a cercaria isolated from a gravel snail (Lithoglyphus naticoides), with a 99.5-100% similarity.

Molecular genetic investigations on Balantidium ctenopharyngodoni Chen, 1955, a parasite of the grass carp (Ctenopharyngodon idella)

Balantidium ctenopharyngodoni is a common ciliate in Hungary, infecting the hindgut of grass carp (Ctenopharyngodon idella), a cyprinid fish of Chinese origin. Although data have already been presented on its occasional pathogenic effect on the endothelium of the host, generally it is a harmless inhabitant of the gut. Phylogenetic analysis of the 18S rDNA and ITS fragments of this protozoan proved that it is in the closest phylogenetic relationship with endocommensalist and symbiont ciliates of mammals feeding on large volumes of green forage, in a similar way as Balantidium spp. known from algae-eating marine fishes.

Histological investigation on Ancyrocephalus paradoxus (Dactylogyridea: Ancyrocephalidae) infection causing mortalities in an intensively cultured pikeperch [Sander lucioperca (L.)] stock

In a cultured pikeperch (Sander lucioperca) stock the monopisthocotylean monogenean gill parasite Ancyrocephalus paradoxus caused heavy infection and mortalities. The gills of the affected fish specimens were infected by 50 to 800 monogenean parasites. Severe pathological changes were found in areas where the worms attached to the gills. At the attachment sites the haptoral discs of the worms formed a deep depression in the epithelium of the filaments, and the anchors pierced into and fixed themselves to the connective tissue of the cartilaginous gill rays. At these attachment sites red blood cells released from injured capillaries were found among the damaged epithelial cells. Around the hooks, anchors and body sections coming into contact with the gill filaments a proliferative tissue developed in which only a remnant of the damaged lamellae was found. Due to the damage caused by the worms the tips of the heavily infected gill filaments fused, formed clubs and were composed of epitheloid-type regeneration tissue lacking respiratory lamellae. In the basal parts of the filaments, where most of the worms attached to the gill, only denuded filaments deprived of lamellae were observed among the cross-sectioned worms in histological sections.

Isolation and characterisation of flavobacteria from wild and cultured freshwater fish species in Hungary

The objective of this study was to survey the incidence of Flavobacterium columnare in wild and cultured freshwater fish species in Hungary. This bacterium usually causes disease in waters of more than 25 °C temperature. However, with the introduction of intensive fish farming systems, infected fish exposed to stress develop disease signs also at lower temperatures; in addition, the temperature of natural waters rises to the critical level due to global warming. Twenty-five isolates from wild and cultured freshwater fishes were identified as F. columnare by specific PCR, although both the fragment lengths and the results of PCRRFLP genotyping with BsuRI (HaeIII) and RsaI restriction enzymes raised doubts regarding this species classification. Sequencing of the 16S ribosomal RNA gene revealed that 23 isolates belonged to the species F. johnsoniae and two represented Chryseobacterium spp. The isolates were found to have high-level multidrug resistance: all were resistant to ampicillin and polymyxin B, the 23 F. johnsoniae strains to cotrimoxazole, 88% of them to gentamicin, and 72% to chloramphenicol. The majority of the 25 isolates were sensitive to erythromycin (88%), furazolidone (76%), and florfenicol (68%).

Parasitic infections of two invasive fish species, the Caucasian dwarf goby and the Amur sleeper, in Hungary

In recent years and decades, two new fish species, the Caucasian dwarf goby (Knipowitschia caucasica) and the Amur sleeper (Perccottus glenii) have become members of the Hungarian fish fauna. In a 14-month study on the parasite fauna of these species, the authors detected 11 parasite species in the Caucasian dwarf goby and 17 species in the Amur sleeper. All parasites found in dwarf goby belong to species commonly occurring also in native Hungarian fishes, but three species (Goussia obstinata, Gyrodactylus perccotti and Nippotaenia mogurndae) collected from the Amur sleeper are introduced species new for the Hungarian fauna.

Three new species of Myxobolus Bütschli, 1882 (Myxozoa: Myxobolidae) infecting the common nase Chondrostoma nasus (L.) in the River Danube

The common nase Chondrostoma nasus (L.) is a frequent cyprinid fish in the River Danube. In a survey on its infection with myxosporeans, eight different Myxobolus spp. spore types were found in the gills, swim bladder, fins and intestinal wall. Of these, spore types representing three species were studied in detail by morphological and molecular methods. Based on the differences in 18S rDNA sequences, two new species of Myxobolus Bütschli, 1882 from the gills and one from the swim bladder are described: M. arrabonensis n. sp., M. szentendrensis n. sp. and M. paksensis n. sp. The new species resembled M. muelleri Bütschli, 1882, M. intimus Zaika, 1965 and M. cycloides Gurley, 1893, all parasitic in leuciscine cyprinids, in spore size and location in the host, but exhibited differences in partial 18S rDNA sequences as follows: M. arrabonensis - M. muelleri (1.4%), M. szentendrensis - M. intimus (2.8%), M. paksensis - M. cycloides (2.4%). Based on the significant differences in rDNA sequences, the three forms are considered to represent new, hitherto undescribed species in spite of their morphological similarities to some Myxobolus spp. forming spores in identical locations in genetically closely related cyprinids of the subfamily Leuciscinae.

Myxozoan infections of the three Indian major carps in fish ponds around Meerut, UP, India, with descriptions of three new species, Myxobolus basuhaldari sp. n., M. kalavatiae sp. n. and M. meerutensis sp. n., and the redescription of M. catlae and M. bhadrensis

New myxosporean species are described from Indian fishes cultured in pond farms of Meerut, Uttar Pradesh (UP) state. Based upon plasmodia found in the Indian major carps (Catla catla, Cirrhinus cirrhosus, Labeo rohita and their hybrids), three new Myxobolus spp., Myxobolus basuhaldari sp. n., Myxobolus kalavatiae sp. n. and Myxobolus meerutensis sp. n., are described, and two species, Myxobolus catlae and Myxobolus bhadrensis, are redescribed. Plasmodia of M. basuhaldari sp. n., M. kalavatiae sp. n., M. meerutensis sp. n. and M. catlae developed in small cysts in the gill lamellae, while plasmodia and scattered spores of M. bhadrensis were found in the muscles and kidney, respectively. Plasmodia and spores found in these fishes differed from each other with respect to their morphology, tissue tropism and 18S ribosomal DNA (18S rDNA) sequence. No major pathological changes were found, but severe infections were observed.

Description of raabeia, synactinomyxon and neoactinomyxum developing stages of myxosporeans (Myxozoa) infecting Isochaetides michaelseni Lastočkin (Tubificidae) in Lake Balaton and Kis-Balaton Water Reservoir, Hungary

Molecular and morphometric investigations were conducted on the actinosporean morphotypes of myxosporeans surveyed in oligochaetes of Lake Balaton and Kis-Balaton Water reservoir. Oligochaetes belonging to the species Isochaetides michaelseni Lastočkin and Branchiura sowerbyi Beddard as well as to the genera Nais Dujardin, Dero Müller and Aeolosoma Ehrenberg were studied during an 18-month period. Actinosporeans were obtained exclusively from I. michaelseni (7,818 specimens) with very low prevalence (0.01-0.06%). Four new actinosporean morphotypes of the collective groups raabeia (2 types), synactinomyxon (1 type) and neoactinomyxum (1 type) were found and described, including the first synactinomyxon collective group from Hungarian biotopes and a new raabeia morphotype. Except for Synactinomyxon type 1, the 18S rDNA analysis revealed that the spores did not match any myxospore entity found in the GenBank.

Tissue preference of some myxobolids (Myxozoa: Myxosporea) from the musculature of European freshwater fishes

For several species of fish myxosporeans known at present, the musculature has been designated as the location of intrapiscine development. In the majority of these cases, plasmodia and spores are actually found in the muscle cells, but there are also myxosporeans that select intermuscular connective tissue, fish bones, nerves and capillaries of the musculature as their site of development. During the plasmodial development of Myxobolus, Henneguya and Thelohanellus species in fish inhabiting Hungarian freshwaters, 3 main locations of development inside the muscles were identified. Pseudodispar-type plasmodia, such as M. cyprini, M. musculi and M. pseudodispar, form plasmodia intracellularly in the muscle cells, while the plasmodia of M. pfeifferi, M. sandrae and T. hovorkai develop in the intermuscular connective tissue. A similar development in the connective tissue of the ventricle and the bulbus arteriosus was observed for M. dogieli, a heart parasite found in some cyprinid fishes. The third type of development is represented by M. tauricus, which prefers the collagenous elements of the fin rays, but its plasmodia are commonly found in the muscle attached to the fish bones.

Myxobolus ophiocarae sp. n. (Myxozoa: Myxosporea: Bivalvulida) infecting the gill of wild goby, Ophiocara porocephala (Perciformes: Gobioidei) in Malaysia

The authors studied the myxosporean infection of wild gobiid fishes (Perciformes: Gobioidei) in the Merang Estuary of Terengganu, Malaysia, and described Myxobolus ophiocarae sp. n. in Ophiocara porocephala. Several myxosporean plasmodia were found intralamellarly within the gill filaments. The spores differed from those of other Myxobolus species previously recorded on gobiid fishes. They were round in valvular view and lens-shaped in sutural view, and had two equal-sized, pyriform polar capsules with polar filaments having six to seven turns. The spores measured 10.34 × 8.79 × 4.53 μm. The 18S rDNA sequence of M. ophiocarae sp. n., based on a contiguous sequence of 1,789 base pairs, differed from any other Myxobolus spp. in GenBank. Phylogenetic analysis of the 18S rDNA gene revealed that this species showed the closest similarity to Myxobolus nagaraensis, Myxobolus lentisuturalis, and Myxobolus cultus.

Integrated circoviral rep-like sequences in the genome of cyprinid fish

Recently a new group of circoviruses have been detected in tissues of Barbel fish and European catfish in Hungary. In our study circovirus genomes were screened in eight additional fish species for the detection and characterization of circoviruses. Two species of these bore circoviral sequences based on conventional PCR assay targeting the replication-associated protein coding gene fragments. Interestingly, the methods successfully used before failed to amplify other parts of the circular viral genome, suggesting the presence of partial, integrated genetic elements in the genome of the host. The successfully sequenced fragments of the Indian rohu (Labeo rohita) encoded mutations which may cause frameshifts or termination in the coding region described previously in other vertebrates. Phylogenetic analyses presumed that integration of the viral genetic elements might have progressed concurrently or following the diversification of cyprinid fish. Further studies on the nature of whole circovirus genomes and integrated elements may help to understand their potential role and evolution in different fish species.

Remarks on the seasonal occurrence and identification of young plasmodial stages of Myxobolus spp. infecting cyprinid fishes in Hungary

During a survey on the Myxobolus infection of two cyprinid fishes, the ide (Leuciscus idus) and the roach (Rutilus rutilus), myxosporean developmental stages were found around the arteries of the gill filaments and in the gill lamellae. An analysis of the 18S rDNA sequences of these stages revealed that plasmodia developing in the ide belonged to Myxobolus elegans, those developing in the gill lamellae of the roach corresponded to M. intimus, while plasmodia developing in close contact with the cartilaginous gill rays proved to be developmental stages of M. feisti. A strict seasonal cycle with a very long intrapiscine development was recorded for M. elegans and M. intimus. Developing plasmodia of the latter Myxobolus spp. occurred from early summer to next spring, and spore formation took place only in April. No seasonality associated with M. feisti infections was found. Developing plasmodia and mature spores of this species occurred simultaneously in different seasons of the year. Myxobolus feisti spore formation always occurred in close contact with the cartilaginous tissue of the gill filaments but spores were rarely encapsulated in the cartilaginous gill rays.

First detection and analysis of a fish circovirus

Circoviruses are present worldwide in birds and pigs but their occurrence in fish has not yet been reported. Recently, increased mortality was observed in barbel fry (Barbus barbus) in Hungary. This paper reports the detection of previously unknown circular viral DNA genomes in barbels by the use of a circovirus-specific wide-range nested PCR. The analysis of two complete genomes (Barbel circovirus, BaCV1 and BaCV2) indicated that they belonged into a new genetic group within the family Circoviridae, distinct from known circoviruses and circovirus-like genomes. Their genome size was 1957 bases and contained two major ORFs similar to the capsid and replication-associated protein genes of circoviruses. A connection between the presence of the virus and clinical manifestations of the infection could not be proved.

An evaluation of indices of gross pathology associated with the nematode Anguillicoloides crassus in eels

This study compares two alternative indices for quantifying the gross pathology of the swimbladder of eels, Anguilla anguilla (L.), infected with the nematode Anguillicoloides crassus. Two observers recorded twice the scores obtained by the two indices on the same set of 71 wild caught eels (from elver to silver eels, French Mediterranean lagoons). The Length Ratio Index (LRI), performed better than the Swimbladder Degenerative Index (SDI), in three of four predefined criteria of decision. First, the LRI better correlated with an estimate of the swimbladder volume reduction, a functional consequence of the infection (representativeness). Also, the LRI was less prone to subjectivity (inter-observer variability) and more precise (intra-observer variability), although less easy to generate (time needed for measurement/assessment). Using a sub-sample of 32 unaffected eels (showing minor if any swimbladder damage and no living worms at autopsy), we ascertained a linear relationship between the swimbladder length and the total body length, a prerequisite of isometric growth, to definitively accept the new ratio index as a valid alternative to the SDI. Also, because the LRI can be recorded on live specimens with radio-imagery (non-invasive method), we recommend its use, and provide a graph of correspondence between the SDI scores, the LRI scores and the estimated proportion of gas loss in the swimbladder.

Infection of the heart of the common bream, Abramis brama (L.), with Myxobolus s.l. dogieli (Myxozoa, Myxobolidae)

Myxobolus dogieli Bykhovskaya-Pavlovskaya & Bykhovski, 1940 is regarded as a site specific myxosporean, infecting the heart of cyprinid fish. During a survey of the myxosporean fauna of Lake Balaton fish, heart myxobolosis was found in the common bream, Abramis brama, with heavy infection of the ventricle and the bulbus arteriosus in some infected bream. Developing and mature plasmodia were mostly in the connective tissue of the subepicardium and subendocardium. Plasmodia developing in the subendocardium protruded into the lumen of the heart, while plasmodia developing in the subepicardium protruded over the epicardium forming large sausage-like outgrowths. Plasmodia with mature spores were found in the summer. The shape and size of the spores corresponded to those of the original description. Phylogenetic analysis based on the 18S rDNA sequence of M. dogieli showed that this species fit well in the genus Myxobolus. As no molecular data are available on spores from the type host, common carp, the species studied by us is temporarily designated as Myxobolus s.l. dogieli.

Description of Myxobolus gayerae sp. n. and re-description of M. leuciscini infecting European chub from the Hungarian stretch of the river Danube

Myxobolus gayerae sp. n. and M. leuciscini González-Lanza & Alvarez-Pellitero, 1985 (Myxozoa: Myxobolidae) have been described and re-described from European chub Leuciscus cephalus L. from the Hungarian stretch of the river Danube. The ellipsoidal plasmodia of M. gayerae sp. n. were found in the mucosa of the intestinal wall, whereas the large, elongated plasmodia of M. leuciscini infected the afferent arteries of the gill filaments. The spores of M. gayerae sp. n. are relatively large, slightly oval and almost rectangular in shape. On the basis of spore morphology and 18S rDNA sequences, the most similar species was M. cycloides Gurley, 1893, but the 2 species differed in host and tissue tropism as well as in the size of the spores. The spores of M. leuciscini from L. cephalus, having no intercapsular appendix or occasionally a very small one, showed a high morphological similarity to spores collected from L. cephalus cabeda, Chondrostoma polylepis and Rutilus arcasi in Spain and described as M. leuciscini González-Lanza & Alvarez-Pellitero, 1985.