Gábor Cech

Morphology, Molecular Data, and Development of Zschokkella mugilis (Myxosporea, Bivalvulida) in a Polychaete Alternate Host, Nereis diversicolor

Abstract The morphology of Zschokkella mugilis Sitjà-Bobadilla and Alvarez-Pellitero, 1993 (Myxosporea, Bivalvulida) in Nereis diversicolor O. F. Müller, 1776 is described for the first time. The molecular data show that the actinospore has 100% similarity to the myxospore of Z. mugilis. Fully mature actinospores are tri-radiate, the spore body has a small process, and the sporoplasm has 2 inner daughter cells. In the polychaete, the spores of the parasite develop in groups of 8 inside pansporocysts. The schizogony phase takes place in the intestinal epithelium, while gametogony and sporogony occur in the coelom of the polychaete. Observations indicate that mature spores are released only during the polychaete reproductive season. Infection was detected only in the winter and spring. In the Aveiro estuary (Portugal), the overall prevalence of infection of the polychaete was 0.5%.

Myxozoan pathogens of Malaysian fishes cultured in ponds and net-cages

We describe new myxosporean species from Malaysian fishes cultured in pond farms and net-cages. Myxobolus omari sp. nov. and M. leptobarbi sp. nov. were found in the muscles of Pangasianodon hypophthalmus and Leptobarbus hoevenii, respectively, while plasmodia and spores of Thelohanellus zahrahae sp. nov. and Henneguya daoudi sp. nov. were detected in the gills of Barbonymus gonionotus and Trichogaster trichopterus, respectively. Plasmodia and spores found in these fishes differed from the known myxosporean species in respect of their morphology, tissue tropism and 18S rDNA structure. No major pathological changes were found, but in the future these species might pose a potential threat to more intensified fish culture.

Myxozoan infections in fishes of the Tasik Kenyir Water Reservoir, Terengganu, Malaysia

During a survey on fishes of the Tasik Kenyir Reservoir, Malaysia, 5 new Myxobolus spp. and 2 known Henneguya spp. were found. The specific locations for 2 Myxobolus spp. were the hosts muscles, while 2 other Myxobolus spp. were found to develop in the hosts kidney and gills, respectively. Of the species developing intracellularly in muscle cells, M. terengganuensis sp. nov. was described from Osteochilus hasselti and M. tasikkenyirensis sp. nov. from Osteochilus vittatus. M. csabai sp. nov. and M. osteochili sp. nov. were isolated from the kidney of Osteochilus hasselti, while M. dykovae sp. nov. was found in the gill lamellae of Barbonymus schwanenfeldii. Henneguya shaharini and Henneguya hemibagri plasmodia were found on the gills of Oxyeleotris marmoratus and Hemibagrus nemurus, respectively. Description of the new and known species was based on morphological characterization of spores, histological findings on locations of plasmodia and DNA sequence data.

Molecular genetic studies on morphologically indistinguishable Myxobolus spp. infecting cyprinid fishes, with the description of three new species, M. alvarezae sp. nov., M. sitjae sp. nov. and M. eirasianus sp. nov.

While studying Myxobolus gill infections of cyprinid fishes, the authors found large, segmented plasmodia in three species: ide (Leuciscus idus), asp (Aspius aspius) and white bream (Blicca bjoerkna). As regards their size and morphology, the spores from these plasmodia corresponded to those of M. dujardini described from chub (Leuciscus cephalus). However, the 18S rDNA sequences of spores from the three cyprinids differed from those of M. dujardini. Based on molecular differences, this paper describes two new species: M. alvarezae sp. nov. from ide and asp, and M. sitjae sp. nov. from white bream. The two new species and M. dujardini had a similar tissue tropism, and infected the multilayered epithelium of the gill filaments. Histological examination of the infected filaments demonstrated that the large plasmodia with multiple buddings were formed from amalgamating small plasmodia. Besides carrying infection in the filamental epithelium, the three above fish species were infected by small intralamellar plasmodia as well. These plasmodia were filled by spores that resembled the roach parasite M. intimus both in morphology and seasonal development. The 18S rDNA sequences of ‘intimus-like’ spores from ide and asp differed only in some base pairs from spores found in the type host roach, and were identified as belonging to M. intimus. The spores found in white bream, however, showed 3.6-5.0% difference in DNA sequence from those of M. intimus; therefore, they have been described as M. eirasianus sp. nov. The aim of this paper was to demonstrate the importance of using molecular methods for separating and identifying morphologically corresponding or closely similar Myxobolus spp.

A new actinospore type Unicapsulactinomyxon (Myxozoa), infecting the marine polychaete, Diopatra neapolitana (Polychaeta: Onuphidae) in the Aveiro Estuary (Portugal)

This work reports a new type of actinospore, Unicapsulactinomyxon, which exhibits a unique morphological characteristic in that it has a single and large polar capsule (9·3×4·1 μm) (which possesses a longitudinally-folded polar filament) instead of the 3 polar capsules previously described for actinosporeans. The spore has a binucleated sporoplasm and 3 valves, each of which forms a long process. The spore has a total length of 241·3 μm. This parasite develops in groups of 8 inside pansporocysts in the coelomic cavity of the polychaete host. Molecular investigations on the SSU rDNA show that the new actinospore type is most closely related to Enteromyxum species (81-84% similarity). A survey of actinospore infections of the marine polychaete Diopatra neapolitana in 2007 and 2009, in the Aveiro Estuary (Portugal), showed an annual prevalence of 1·0% and 0·3%, respectively.

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.

Myxobolus species infecting the cartilaginous rays of the gill filaments in cyprinid fishes

During a survey on myxosporean parasites of cyprinid fishes in Hungary, Myxobolus infections were found in the cartilaginous rays of the gill filaments in roach (Rutilus rutilus) and bleak (Alburnus alburnus). Myxobolus spp. causing the infections were studied by morphological, histological and molecular methods. Small plasmodia surrounded by chondrocytes contained relatively few spores which differed from each other and from the known Myxobolus spp. both in their morphology and 18S rDNA sequences. Both species, described as M. feisti sp. nov. and M. susanlimae sp. nov., are characterised by a specific cartilaginous histotropism.

Myxobolus erythrophthalmi sp. n. and Myxobolus shaharomae sp. n. (Myxozoa: Myxobolidae) from the internal organs of rudd, Scardinius erythrophthalmus (L.), and bleak, Alburnus alburnus (L.)

During a survey of myxosporean parasites of cyprinid fish in Hungary, infections caused by unknown Myxobolus spp. were found in the internal organs of rudd, Scardinius erythrophthalmus, and bleak, Alburnus alburnus. Small plasmodia developed in blood vessels of the kidney, liver, testes and intestinal wall. The parasites were studied on the basis of spore morphology and by histological and molecular methods. In most cases, plasmodia were surrounded by host tissue without a host reaction; however, in advanced cases, a connective tissue capsule was seen around plasmodia. Spores collected from the two fish species differed from each other and from the known Myxobolus spp. both in their morphology and 18S rDNA sequences. The two species, described as M. erythrophthalmi sp. n. from rudd and M. shaharomae sp. n. from bleak, are characterized by a specific histotropism to blood vessels, while the organ specificity involves the kidney and for the latter species, most internal organs.

A novel myxozoan parasite of terrestrial mammals: description of Soricimyxum minuti sp. n. (Myxosporea) in pygmy shrew Sorex minutus from Hungary.

As part of a biodiversity study in northwestern Hungary, we conducted a parasitological survey of small mammals. In both common shrews (Sorex araneus Linnaeus) and pygmy shrews (Sorex minutus Linnaeus), we found myxospores of a species of Soricimyxum Prunescu, Prunescu, Pucek et Lom, 2007 (Myxosporea) and plasmodia in the bile ducts within the liver. Spores from both species of shrewswere morphologically and morphometrically indistinguishable, but differed in their SSU rRNA gene sequences by 3.3%. We identified spores and developmental stages from the common shrew as Soricimyxum fegati Prunescu, Prunescu, Pucek et Lom, 2007, based on morphometric data and DNA sequence similarity. Spores from the pygmy shrew were only 96.7% similar to S. fegati, hence we identified them as a novel myxosporean Soricimyxum minuti sp. n. This is only the second myxosporean parasite species described from mammals.

Ortholinea auratae n. sp. (Myxozoa, Ortholineidae) infecting the urinary bladder of the gilthead seabream Sparus aurata (Teleostei, Sparidae), in a Portuguese fish farm

A new myxosporean species, Ortholinea auratae n. sp., is described from the gilthead seabream, Sparus aurata Linnaeus, 1758 (Teleostei, Sparidae) from a fish farm in Algarve, Portugal. Plasmodia and spores were found in the urinary bladder and, less frequently, in the posterior kidney. Plasmodia were polymorphic, presenting an irregular cellular membrane due to the presence of several peripheral projections, which in turn were covered by a glycocalyx-like sheet. Mature spores were subspherical in valvular view and ellipsoidal in sutural view, measuring 9.0 ± 0.3 (8.2–10.1) μm in length, 8.3 ± 0.4 (7.5–9.1) μm in width, and 7.2 ± 0.5 (6.3–8.4) μm in thickness. The two valves comprising the spores displayed an intricate pattern of surface ridges and were also enveloped by a glycocalyx-like sheet. Two subspherical polar capsules, 3.2 ± 0.1 (2.9–3.6) μm long and 2.7 ± 0.1 (2.4–2.9) μm wide, were located at the anterior pole and displayed divergent orientation. The polar filament coiled in three to four turns. The comprehensive analysis of the parasite’s ultrastructural observations and molecular data for the small subunit (SSU) ribosomal DNA (rDNA) gene identify O. auratae n. sp. as a new species, clustering together with other myxosporeans infecting the excretory system to form a subclade of the main freshwater clade.