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  • Author or Editor: Csaba Székely x
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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.

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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.

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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.

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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.

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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.

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Authors: Réka Borzák, Kálmán Molnár, Gábor Cech and Csaba Székely

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.

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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.

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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.

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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.

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Abstract

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.

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