Updated morphology, histopathology and molecular phylogeny of Myxobolus hearti, cardiac myxosporea in gibel carp, Carassius gibelio (Bloch)

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.

Morphological and molecular description of a new species of Myxobolus (Myxosporea: Myxobolidae) infecting Planiliza macrolepis (Smith, 1846) from India

The present paper describes a novel species of Myxobolus parasitizing the gill filaments of the largescale mullet, Planiliza macrolepis from Cochin backwaters, Kerala, India. The parasite develops in the gill filaments; plasmodia elongated, milky white, measured 1.37-2.18 (1.78 ± 0.35) mm × 0.07-0.12 (0.10 ± 0.02) mm in size. Mature myxospores ovoid in valvular view, biconvex in sutural view with smooth shell valves and measured 6.24-7.02 (6.63 ± 0.23) × 5.01-6.18 (5.68 ± 0.25) μm in size. Polar capsules equal, oval with pointed anterior ends, 3.07-3.58 (3.33 ± 0.12) × 1.68-2.42 (2.09 ± 0.18) μm in size. Polar filaments with 4 coils, measured 29.61 ± 4.75 μm in length when extruded. Sporoplasm binucleate with a rudimentary nucleus and a vacuole. A comparison with related Myxobolus species revealed significant morphological and morphometric differences. In BLASTN and genetic distance analysis, the present parasite showed high divergence with other myxosporean sequences, indicating its molecular uniqueness. In Maximum Likelihood and Bayesian Inference analysis, the present species stands out with M. ramadus as sister branch within the Myxobolus clade. In infected gill filaments, the plasmodia caused swelling/deformation, compression of lamellae and reduction in respiratory surface area. Three of 222 P. macrolepis screened were infected, indicating a prevalence of 1.3%. Considering the morphological, morphometric, molecular and phylogenetic differences with the previously described species of myxosporeans, along with the dissimilarities in host and geographical locations, the present parasite is treated as a new species and the name Myxobolus cochinensis n. sp. is proposed.

Native parasite affecting an introduced host in aquaculture: cardiac henneguyosis in the red seabream Pagrus major Temminck & Schlegel (Perciformes: Sparidae) caused by Henneguya aegea n. sp. (Myxosporea: Myxobolidae)

Background

Henneguya Thélohan, 1892 (Myxobolidae) is one of the most species-rich genera of myxosporean parasites infecting fish. Although common in nature, there are few reports of these parasites causing important disease in aquaculture. In this paper, we describe a new species of Henneguya infecting Pagrus major (Temminck & Schlegel), a fish host introduced to the Mediterranean Sea from Japan in the late 1980s.

Results

Large plasmodia of the parasite were found in the bulbus arteriosus and in the ventricle of the infected fish. Spores were found mainly in the kidney and heart and were accompanied by melanized macrophages or vascular intimal proliferation mixed with a mild non-suppurative response, respectively. Comparisons of morphometric data for spore and polar capsule length and width, suggest a unique combination of features in the newly described species. Molecular analysis, based on 18S rDNA sequence of the parasite, followed by phylogenetic analysis, indicated that the parasite described here is a novel species of Henneguya, clustered with the marine congeneric species.

Conclusions

Henneguya aegea n. sp. infects in aquaculture P. major, a host introduced as eggs to the Mediterranean from Japan. Despite the high host specificity of the myxobolid parasites, H. aegea n. sp. seems to be able to use P. major as a host and propagate successfully, causing morbidity and mortality. This could result in spillback of the new species from high density cultured non-native P. major to native fish hosts.

Morphological, histological and molecular characterization of three Myxobolus species (Cnidaria: Myxosporea) from silver carp Hypophthalmichthys molitrix Valenciennes and bighead carp Hypophthalmichthys nobilis Richardson in China

Three Myxobolus species were obtained from silver carp Hypophthalmichthys molitrix Valenciennes and bighead carp Hypophthalmichthys nobilis Richardson in China. In the present study, we supplemented their taxonomic characteristics by the morphological, histological and molecular methods. Myxobolus kiuchowensis Chen in Chen et Ma, 1998 formed small ellipsoidal plasmodia in the intestinal wall of bighead carp. Its spores appeared asymmetrical obovate in frontal view and fusiform in lateral view. Tiny mamillary protrusion in the anterior of some spores was observed. Two pyriform polar capsules were unequal. Histologically, M. kiuchowensis infected the tunica muscularis of host intestine. Myxobolus abitus Li et Nie, 1973 formed sausage-like plasmodia in the gills of silver carp. Its spores appeared oblate in frontal view and fusiform in lateral view. Two pyriform polar capsules were unequal and an obvious inter-capsule appendix was observed. Histological examination revealed that M. abitus developed in the interlamellar-epithelium of host gills. Myxobolus pavlovskii (Akhmerov, 1954) Landsberg et Lom, 1991 formed sausage-like plasmodia both in the gills of silver carp and bighead carp. Spores of M. pavlovskii were proximate oval in frontal view and fusiform in lateral view. Two pyriform polar capsules were unequal. The BLAST search indicated the SSU rDNA sequences of M. kiuchowensis and M. abitus were not identical to any sequence, however, the SSU rDNA sequences of M. pavlovskii were identical to that of M. pavlovskii recorded previously. Phylogenetic analysis showed that the present three species robustly clustered together in Cyprinid group and Asia group.

Development of monoclonal antibodies against polar filaments and spore valves of Myxobolus honghuensis (Myxosporea: Bivalvulida)

Myxobolus honghuensis infects the pharynx of allogynogenetic gibel carp Carassius auratus gibelio (Bloch) and can cause high mortality. Only morphology-based diagnostic methods are currently available for clinical samples, but these methods are laborious and have low efficiency of detection. To overcome this problem, we designed a more sensitive diagnostic method. Two monoclonal antibodies (MAbs 1C7 and 3B7) were prepared by immunizing mice with soluble protein from sonicated M. honghuensis spores. Immunofluorescence analysis revealed that MAb 1C7 specifically reacts with polar filaments from spores, whereas MAb 3B7 identified protein localized on the spore valves. The isotypes of MAb 1C7 and MAb 3B7 were IgM and IgG1, respectively. Results of Western blot analysis revealed that MAb 1C7 recognized 2 prominent protein bands with molecular weights of 130 and 180 kDa, while MAb 3B7 recognized a protein band of 28 kDa. Thus, in this study we have developed 2 MAbs that have the potential for efficient detection of M. honghuensis. Moreover, identification of MAb 1C7 and MAb 3B7 allows for further studies of the functions and biochemical composition of polar filament and spore surface antigens.

Henneguya doneci (Myxosporea: Bivalvulida) in the gill filaments of Prussian carp Carassius gibelio (Bloch) from the upper Yellow River running through Inner Mongolia, China

We examined 11 Prussian carp, Carassius gibelio (Bloch), from the upper Yellow River running through Inner Mongolia (Wuhai City) to record myxosporean species. Between 6 and 15 elongated cysts of Henneguya doneci were located at the basal part of the gill filaments of 3 carp (27.3%); no more myxosporean plasmodia were found in other organs. Although the morphology and morphometric values of the spores (average measurements of 14 spores in µm: 11.4 long by 9.2 wide with 7.5 in thickness; 2 polar capsules, equal, 5.5 long by 3.2 wide; and a bifurcated caudal process, 51.6 long) with an evident intercapsular appendix were basically coincident with the species, the dimensions of the spore bodies were marginally larger, and the length of the caudal processes was distinctly longer than previously reported values for H. doneci (44.2-59.2 µm vs. 26.8-42.6 µm, respectively). Genetic analysis of the 18S ribosomal RNA gene (rDNA) found few nucleotide substitutions when compared with 3 deposited sequences of H. doneci collected around the Yangtze River (Sichuan and Hubei Provinces), China, indicating that the uniqueness of some of the morphological features exhibited by the present Wuhai isolate should be ascribed to intraspecific variation.

Thelohanellus wangi n. sp. (Myxozoa, Myxosporea), a new gill parasite of allogynogenetic gibel carp (Carassius auratus gibelio Bloch) in China, causing severe gill myxosporidiosis

We describe here a new myxozoan, Thelohanellus wangi n. sp., infecting the allogynogenetic gibel carp, Carassius auratus gibelio (Bloch), in a fry nursery farm in Jiangsu Province, China. Polysporous gray white round or ovoid plasmodia, 500-1,500 μm in size, were found exclusively in the gill filaments. The diagnostic characteristics of the myxospores are as follows: spore melon seed shaped in frontal view with smooth surface and asymmetrical valves; convex-shaped in sutural view with straight or slightly bent and thick sutural line, averaging 20.2 (16.5-22.3) × 9.9 (9.1-10.8) × 9.3 μm (8.2-10.4) in size; and one elliptical polar capsules with subulate anterior end and round posterior end, averaging 10.1 (8.4-11.2) × 6.5 μm (6.1-7.0) in size. Polar filaments coil six to seven turns and are slightly oblique to the longitudinal axis of the polar capsule. An elongate melon seed-shaped mucus envelope surrounds almost completely the spore, but with largest distance in posterior end between spore valve and mucus envelope. Granular sporoplasm contains two slightly oval nuclei, and no iodinophilous vacuole is observed. Histopathological analysis showed that the plasmodia embedded in the gill filaments and occasionally extended into the connective tissue of the gill arch. No significant inflammatory responses were provoked by the infection. The development of parasite is asynchronous, with mature spores centrally locating and trophozoites and pre-sporogonic stages peripherally locating within the plasmodia. Overall prevalence was 74% (37/50). Infection intensity was usually high, with about 10-30 cysts per fish. Phylogenetical analysis shows that T. wangi n. sp. is most closely related to several Thelohanellus species infecting cyprinid fish and formed a Thelohanellus clade based on the ribosomal DNA data. The cysts of this myxosporean were only found from fry seed with body length below 7 cm, generally from late April to early June when the fry fish of allogynogenetic gibel carp were nursed in the epizootic areas.

Synopsis of the species of Myxobolus Bütschli, 1882 (Myxozoa: Myxosporea, Myxobolidae) described between 2005 and 2013

A synopsis of the species of Myxobolus Bütschli, 1882 (Myxozoa, Myxosporea, Myxobolidae) described between 2005 and 2013 is presented, including 112 nominal species. For each species the most important morphological and morphometric features are indicated in tabulated format. Included are also accession numbers for molecular data (when available), site of the infection within the host, features of the vegetative stage, organ infected, etc., plus a full bibliography of the original records for these species.