The life cycle of Myxobolus lentisuturalis (Myxozoa: Myxobolidae), from goldfish (Carassius auratus auratus), involves a Raabeia-type actinospore

Clinical, histopathological and phylogenetic analysis of Myxobolus lentisturalis (Myxozoa: Myxobolidae) infecting the musculature of farmed population of goldfish (Carassius auratus) in Iran: 2021-2022

There is a claimed increase in the global prevalence and incidence of emerging diseases observed in many organisms. Myxozoa represents an essential group of metazoan parasites that hold both economic and ecological significance. In the current study, 1% of the fish population at two commercial goldfish (Carassius auratus) farms in Tehran and Ghom province, Iran, developed cavitating muscular lesions resembling humps in February 2021 and January 2022. Fish displaying pathological abnormalities were transported to the Ornamental Fish Clinic and subjected to clinical examination. Light microscopy was subsequently used to examine wet smears of skin and gills, as well as whitish exudate. In addition, tissue homogenates were collected for more precise identification and molecular confirmation. The study discovered that individuals from the goldfish farms were infected with the pathogenic myxozoan Myxobolus lentisuturalis, which caused significant damage to the epaxial muscles. The spores collected from the humps had a lack of uniformity and were primarily ellipsoidal in shape. Histopathological analysis also revealed parasites in various stages of development, such as plasmodia and spores, as well as inflammatory cell infiltration (macrophage, giant cell and lymphoplasmacytic infiltration) between skeletal muscle fibers. Phylogenetic analysis of M. lentisuturalis was performed by using MEGA 11 and the maximum likelihood method. M. lentisuturalis is a myxozoan parasite that has been sparsely recorded and lacks widespread recognition. The current study is the first clinical, histopathological, and molecular characterization of M. lentisuturalis isolated from the skeletal musculature of goldfish (C. auratus) in Iran.

First record and description of actinospore stages (raabeia, triactinomyxon, and aurantiactinomyxon types) of fish parasitic myxozoans from Malaysia

During a 2-month survey in 2023 at Tasik Telabak, Terengganu, Malaysia three distinct actinospore types, namely raabeia, triactinomyxon and aurantiactinomyxon were identified in three invertebrate host species: Aulodrilus acutus, Branchiodrilus sp., and Bothrioneurum sp. utilizing morphometric and molecular analyses. Maximum likelihood of 18S rDNA positioned the raabeia type within the Myxobolus clade from fish of the Order Cypriniformes, suggesting a detected actinospore has a potential life cycle development in Cypriniformes and the genus Myxobolus. Both triactinomyxon and aurantiactinomyxon types were described solely based on morphology and morphometrics due to preservation error preventing the acquisition of 18S rDNA sequences. The triactinomyxon type in this study exhibited distinct morphology in spore shape and dimensions, characterized by a short style and caudal processes. Conversely, the aurantiactinomyxon type described herein possesses prominent elongated pyriform polar capsules not resembling any previously known aurantiactinomyxon types. These distinctive features, along with host species and geographical location justify their classification as novel types. Histological and microscopic analyses revealed the development of pansporocysts in the intestinal epithelium of the oligochaete host. This study marks the first descriptions of actinospore stages of myxozoans in Malaysia and the initial report of actinospores infecting host species of Aulodrilus acutus, Branchiodrilus sp. and Bothrioneurum sp.

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.

Involvement of sphaeractinomyxon in the life cycle of mugiliform-infecting Myxobolus (Cnidaria, Myxosporea) reveals high functionality of actinospore morphotype in promoting transmission

Four new actinospore types belonging to the sphaeractinomyxon collective group (Cnidaria, Myxosporea) are described from the coelomic cavity of a marine Baltidrilus sp. (Oligochaeta, Naididae) inhabiting a northern Portuguese estuary. Host identification supports the usage of marine oligochaetes, namely of the family Naididae Ehrenberg, 1828, as definitive hosts for myxosporeans inhabiting estuarine/marine environments. The absence of mixed infections in the host specimens analysed is suggested to reflect the influence of host-, parasite- and environmental-related factors regulating myxosporean-annelid interactions. Molecular analyses matched the SSU rDNA sequences of three of the four new types with those of mugiliform-infecting Myxobolus spp., namely Myxobolus mugiliensis and a Myxobolus sp. from flathead grey mullet Mugil cephalus, and Myxobolus labrosus from thicklip grey mullet Chelon labrosus. These results directly link, for the first time, the sphaeractinomyxon collective group to a myxospore counterpart, further confirming their previously hypothesized specific involvement in the life cycle of myxobolids that infect mullets. Acknowledging this life cycle relationship, the functionality of the sphaeractinomyxon morphotype is suggested to have been decisive for the evolutionary hyperdiversification of the genus Myxobolus in mullets. Unlike other actinospore morphotypes, sphaeractinomyxon lack valvular processes, which implies a limited capability for buoyancy. Considering the benthic-feeding nature of mullets, this feature is most likely crucial in promoting successful transmission to the vertebrate host.

New actinosporean description prompts union of the raabeia and echinactinomyxon collective groups (Cnidaria, Myxozoa)

We describe, morphologically and molecularly, a new actinosporean from the intestinal epithelium of the freshwater oligochaete Ilyodrilus templetoni in the upper estuary of the River Minho, Northern Portugal. Mature actinospores resembled both echinactinomyxon and raabeia types, emphasizing the previously known lack of a clear boundary between these 2 collective groups. Historically, raabeia and echinactinomyxon types have been differentiated solely based on the shape of the valvular processes being curved or straight, respectively. Our observations, however, show that this morphological character is too variable for distinguishing between these 2 collective groups, since the actinospores of the raabeia described here displayed valvular processes that could either be straight, downward or upward curved. Several similar cases can be found in the available literature. Considering this overlap in actinospore morphology, we propose that echinactinomyxon be deemed invalid and its types be included in raabeia, as the latter constitutes the older of the 2 groups. Known echinactinomyxon types, however, should not be renamed as raabeia, as this would create unnecessary confusion. Accordingly, a more comprehensive definition of the raabeia collective group is provided. Phylogenetic analyses revealed polyphyletic clustering of raabeia/echinactinomyxon types among members of the myxosporean suborders Variisporina and Platysporina, reiterating the lack of agreement between actinosporean morphotypes and myxosporean genera. The new type described here specifically clusters within the Paramyxidium clade, alongside other SSU rDNA sequences of raabeia, echinactinomyxon, aurantiactinomyxon and synactinomyxon. Considering that most Paramyxidium spp. parasitize Anguilla anguilla (Linnaeus, 1758), future myxozoan surveys in the River Minho should include this species.

Parasite Dispersal From the Ornamental Goldfish Trade

Goldfish, Carassius auratus Linnaeus, 1758, are immensely popular ornamental cyprinid fish, traded in more than 100 countries. For more than 500 years, human translocation has facilitated the spread of goldfish globally, which has enabled numerous and repeated introductions of parasite taxa that infect them. The parasite fauna assemblage of goldfish is generally well documented, but few studies provide evidence of parasite coinvasion following the release of goldfish. This review provides a comprehensive synopsis of parasites that infect goldfish in farmed, aquarium-held, native, and invasive populations globally and summarises evidence for the cointroduction and coinvasion of goldfish parasites. More than 113 species infect goldfish in their native range, of which 26 species have probably coinvaded with the international trade of goldfish. Of these, Schyzocotyle acheilognathi (Cestoda: Bothriocephalidae), Ichthyophthirius multifiliis (Ciliophora: Ichthyophthiriidae), Argulus japonicus (Crustacea: Argulidae), Lernaea cyprinacea (Crustacea: Ergasilidae), Dactylogyrus anchoratus, Dactylogyrus vastator and Dactylogyrus formosus (Monogenea: Dactylogyridae) are common to invasive goldfish populations in more than four countries and are considered a high risk of continued spread. Coinvasive parasites include species with direct and complex life cycles, which have successfully colonised new environments through utilisation of either new native hosts or suitable invasive hosts. Specifically, I. multifiliis, A. japonicus and L. cyprinacea can cause harm to farmed freshwater fish species and are important parasites to consider for biosecurity. These species may threaten other aquatic animal industries given their low host specificity and adaptable life histories. Future attention to biosecurity, management and border detection methods could limit the continued spread of exotic parasites from the ornamental trade of goldfish.

Morphological and molecular characterization of actinosporeans infecting oligochaete Branchiura sowerbyi from Chinese carp ponds

We surveyed the actinosporean stages of fish myxosporeans at fish farms in Jiangsu Province, China, from 2011 to 2014. During the surveys, we identified 7 actinosporean types from 4 collective groups: echinactinomyxon (1 type), triactinomyxon (1 type), aurantiactinomyxon (1 type), and neoactinomyxum (4 types), released by the oligochaete Branchiura sowerbyi. The morphological characteristics and DNA sequences of these types are described here. Based on 18S rDNA sequence analysis, the actinosporean of echinactinomyxon type CZ with 4 branches at the end of the caudal processes was identified as Myxobolus wulii, and the neoactinomyxum type JD was identified as Thelohanellus wangi Yuan, Xi, Wang, Xie, Zhang, 2015 (JX458816), a recently nominated species from the gills of allogynogenetic gibel carp Carassius auratus gibelio. In addition, actinosporeans of aurantiactinomyxon type JD, neoactinomyxum type CZ-1, neoactinomyxum type CZ-2, and neoactinomyxum type CZ-3 showed high genetic similarity to T. wuhanensis (96.3-96.5%), T. nikolskii (98.0-99.1%), T. wuhanensis (97.8-98.9%), and T. hovorkai (98.7-98.9%), respectively. Phylogenetic analyses showed that these actinosporeans were robustly clustered in the Thelohanellus spp. clade.

Molecular and morphological characterization of myxozoan actinospore types from a commercial catfish pond in the Mississippi delta

The actinospore diversity of infected Dero digitata was surveyed (May 2011) from a channel catfish (Ictalurus punctatus) production pond in the Mississippi Delta region for the elucidation of unknown myxozoan life cycles. At present, only 2 myxozoan life cycles have been molecularly confirmed in channel catfish, linking the actinospore stage from an aquatic oligochaete (D. digitata ) and the myxospore stage from the catfish. In this study D. digitata (n = 2,592) were isolated from oligochaetes collected from the bottom sediment of a channel catfish production pond. After 1 wk of daily observation, a total of 6 genetically different actinospore types were observed. The collective groups were classified as 2 aurantiactinomyxons, 2 helioactinomyxons, 1 raabeia, and 1 triactinomyxon. Overall prevalence of myxozoan infections in the isolated oligochaetes was 4.4%. Actinospores were photographed and measured for morphological characterization. Four previously undescribed actinospore types were identified and characterized molecularly and morphologically. Phylogenetic analysis revealed the raabeia and one of the helioactinomyxon (type 1) actinospores were closely related to the group of myxozoans known to parasitize ictalurids in North America. To date, no myxospores have been linked to the newly sequenced actinospores reported in this survey. The morphological and molecular data generated from this study will assist in the identification of myxospore counterparts for these actinospore stages and aid in the elucidation of unknown myxozoan life cycles in closed production systems.

Small subunit ribosomal RNA sequence links the myxospore stage of Henneguya mississippiensis n. sp. from channel catfish Ictalurus punctatus to an actinospore released by the benthic oligochaete Dero digitata

There are more than 200 species of Henneguya described from fish. Of these, only three life cycles have been determined, identifying the actinospore and myxospore stages from their respective hosts. Two of these life cycles involve the channel catfish (Ictalurus punctatus) and the freshwater oligochaete Dero digitata. Herein, we molecularly confirm the life cycle of a previously undescribed Henneguya sp. by matching 18S ribosomal RNA (rRNA) gene sequence of the myxospore stage from channel catfish with the previously described actinospore stage (Aurantiactinomyxon mississippiensis) from D. digitata. Gill tissue from naturally infected channel catfish contained pseudocysts restricted to the apical end of the primary lamellae. Myxospores were morphologically consistent with Henneguya spp. from ictalurid fishes in North America. The spores measured 48.8 ± 4.8 μm (range = 40.7-61.6 μm) in total spore length. The lanceolate spore body was 17.1 ± 1.0 μm (14.4-19.3 μm) in length and 5.0 ± 0.3 μm (4.5-5.5 μm) in width. The two polar capsules were 6.2 ± 0.4 μm (5.8-7.0 μm) long and 5.0 ± 0.3 μm (4.5-5.5 μm) wide. The polar capsule contained eight to nine coils in the polar filament. The two caudal processes were of equal length, measuring 31.0 ± 4.1 μm (22.9-40.6 μm). The 1980-bp 18S rRNA gene sequence obtained from two excised cysts shared 99.4% similarity (100% coverage) to the published sequence of A. mississippiensis, an actinospore previously described from D. digitata. The sequence similarity between the myxospore from channel catfish and actinospore from D. digitata suggests that they are conspecific, representing alternate life stages of Henneguya mississippiensis n. sp.

Life cycles of three Myxobolus spp. from cyprinid fishes of Lake Balaton, Hungary involve triactinomyxon-type actinospores

A study on the actinosporean fauna of oligochaetes of Lake Balaton was carried out from 2009 to 2011. The morphology of actinosporean stages of myxosporeans obtained from oligochaetes was studied, and their 18S rDNA structure was analyzed by molecular biological methods. Three triactinomyxon types were released from the oligochaete Isochaetides michaelseni (Tubificidae). The sequences of Triactinomyxon type 1 proved to be identical with those of Myxobolus fundamentalis. The sequences of Triactinomyxon type 2 showed 99.9% similarity to Myxobolus eryhtrophthalmi, while the sequences of Triactinomyxon type 3 showed a 99.9% similarity to those of Myxobolus shaharomae. The life cycles of the above species, just like those of other species with a known life cycle, suggest that most Myxobolus spp. develop through triactinomyxon-type actinosporean stages.

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.

Identification and characterization of one novel type of Triactinospomyxon with short spore axis

This study identifies and characterizes one novel type of triactinospomyxon in oligochaete specimen of Branchiura sowerbyi Beddard collected from a fish pond used for rearing gibel carp located in Caidian Experimental Station of the Institute of Hydrobiology. It is nominated as Triactinospomyxon caidianensis type. The spore is of characteristic triactinomyxon "anchor" shape and possesses a spore body with sporoplasm containing 32 germ cells, 3 polar capsules, and 3 caudal processes. Compared with other triactinomyxon spores described previously, T. caidianensis type has a short spore axis with 76.5 μm in length and a very short style with 38.9 μm in length. Molecular analyses on 18S rDNA sequences indicate that the novel T. caidianensis type is most closely related to Triactinomyxon sp SA-2005, Antonactinomyxon sp KAB-2001, and Synactinomyxon sp KAB-2001 with 80.33% to 81.92% identities. On the basis of spore morphology and genetic data, the T. caidianensis type presented in this paper differs from those already known and described in the literatures.

The development of Myxobolus pavlovskii (Myxozoa: Myxobolidae) includes an echinactinomyxon-type actinospore

Echinactinomyxon-type actinospores were found in a mixed-species oligochaete culture originating from the Temperate Water Fish Hatchery near Budapest, Hungary. On the basis of DNA sequence analysis, the actinospores were identified as Myxobolus pavlovskii (Akhmerov, 1954), the 18S rDNA sequence from myxospores of which is available in GenBank. Silver carp Hypophthalmichthys molitrix (Valenciennes) fry specimens were successfully infected by cohabitation with the echinactinomyxon-releasing oligochaetes, which confirmed the molecular data congruence. The echinactinomyxons and the myxospores that developed in the gills of exposed fish fry were analysed morphologically and on DNA basis. The infected gill tissue was examined histologically. As typical characters of M. pavlovskii, numerous small plasmodia were observed in the epithelia of gill lamellae. Plasmodia contained thousands of myxospores with polar capsules unequal in size and witl; large intercapsular processes. The 18S rDNA sequence from actinospores and those from myxospores originating from the experimentally infected fish were identical. The oligochaete species releasing actinospores was morphologically determined as Limnodrilus sp. This is the first record of an echinactinomyxon as an alternate stage within the genus Myxobolus.