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  • Author or Editor: Edit Eszterbauer x
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Two, morphologically indistinguishable myxosporean species, Myxobolus elegans Kashkovsky, 1966 and M. hungaricus Jaczó, 1940 were differentiated using molecular biological methods. Polymerase chain reaction (PCR) with primers specific for the family Myxobolidae was used to amplify an approximately 1600 base pairs (bp) long fragment of the 18S ribosomal RNA gene. In restriction fragment length polymorphism (RFLP) study with HinfI, MspI and TaqI enzymes, the two parasite species were easily distinguishable. The genetic distinctness was also confirmed by the DNA sequence of their PCR products. Although M. elegans and M. hungaricus are morphologically very similar, based on the results of the PCR-RFLP and the DNA sequences, we concluded that they are valid species.

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The genetic relatedness of two kidney-parasitic Sphaerospora species was studied. Although S. renicola, the causative agent of swimbladder inflammation of common carp fingerlings (Cyprinus carpio), and Sphaerospora sp. originating from goldfish (Carassius auratus auratus) were indistinguishable on the basis of spore morphology, they were found to be genetically different as their 18S rDNA sequences shared only 71.9% identical nucleotides. In the phylogenetic trees, Sphaerospora sp. from goldfish grouped with Myxidium truttae (AJ582061) within the clade of the coelozoic freshwater species. Sphaerospora renicola clustered with S. molnari (AF378345) within the group of myxosporeans histozoic in gills. The topology of the six Sphaerospora species on the phylogenetic trees implied that myxospore morphology does not correlate with the genetic relationships, and the genus seems to be polyphyletic.

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Here, we experimentally studied the site preference of Myxobolus cerebralis, one of the most pathogenic myxozoan (Cnidaria, Myxozoa) fish parasites, which causes whirling disease in salmonids. Parasite invasion was examined in three fish species with various susceptibility levels: the type host brown trout, the highly susceptible rainbow trout, and the non-susceptible gibel carp, in which parasite spores do not develop. We investigated the first two hours of fish invasion, and measured the site preference of triactinomyxons (TAMs) during attachment and penetration of fish in three body parts (gills, fins, skin). Infection prevalence and intensity were estimated using a species-specific nested PCR, optimised in the present study. The highest infection prevalence was detected in the most susceptible fish species, rainbow trout. Interestingly, higher prevalence was observed in gibel carp than in the type host, brown trout (95.2% vs. 85.7%). Considering body locations, remarkable differences were detected in infection intensities. The highest intensity was observed in fins, whereas skin was the least infected body part in every fish species examined. Infection prevalence and intensity did not differ significantly among fish species. Thus, we confirmed that M. cerebralis TAMs cannot discern fish species. Furthermore, we proved experimentally that fish fin is significantly more attractive to fish-invading parasite TAMs than gills or skin.

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One of the main obstacles in freshwater aquaculture is the parasitic ciliate Ichthyophthirius multifiliis (Ich), the causative agent of white spot disease. The use of immunostimulants as feed additives may be a promising approach to control Ich infection. In the present study, we tested the prophylactic effect of orally administered β-1,3/1,6-glucan and propolis extract E50 against Ich infection in common carp. In total, 122 fish were separated into three experimental groups fed with a control, 3% β-glucan and 1% propolis diet for 40 consecutive days, respectively. On day 40, 16 fish per group were individually exposed to Ich theronts and the number of trophonts was counted 5 days post exposure. Relative gene expression of interleukin 1-β (IL-1-β) in common carp liver was examined by qPCR. Compared to control, the mean infection intensity was lower in the β-glucan- and propolis-fed groups; however, the difference was not statistically significant. The relative expression of IL-1-β significantly decreased in the propolis-fed group at day 10. In the β-glucan-fed group, a significant IL-1-β decrease was detected at day 15 compared to control. Although the Ich infection intensity was slightly decreased in both treated groups, and IL-1-β was moderately down-regulated in the liver of common carp, our results suggest that the applied feeding regime is insufficient to prevent Ich outbreaks in common carp.

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