Phylogenetic relationships of three Kudoa spp. with morphologically similar myxospores (K. iwatai, K. lutjanus, and K. bora), with the redescription of K. uncinata and K. petala and description of a new species (K. fujitai n. sp.) in fishes in the South China Sea

Description of three new species of Kudoa Meglitsch, 1947 (Myxozoa: Multivalvulida) in commercial marine fishes from southern China, and new host records

Multivalvulidan myxosporeans (Multivalvulida) of the genera Unicapsula Davis, 1924 and Kudoa Meglitsch, 1947 are mostly causative agents of latent and imperceptible infection in marine fishes. However, they are sometimes incriminated in causing post-mortem myoliquefaction or unsightly cyst formation in commercial fish. Despite the great commercial impacts of multivalvulidan infection, the biodiversity, host range and epidemiology of multivalvulidan species remain to be explored further, including infection of alternative annelid hosts. Therefore, this study aimed to identify multivalvulidan species and their host and/or distribution records in commercial fishes in China. Multivalvulidan infection was detected in ten commercial fish species of seven families from the South and East China Seas (Northwest Pacific Ocean) and the Eastern Central Atlantic Ocean (an imported Dagetichthys lusitanicus [de Brito Capello]). Based on morphological and molecular-genetic analyses of their small and large subunit of ribosomal RNA genes, five new host and/or geographical distribution records for five fish species are presented, and three new species in five fish species are described, namely Kudoa neoscomberomori sp. n. in Scomberomorus commerson (Lacépède); Kudoa pilosa sp. n. in Helicolenus hilgendorfi (Döderlein) (type host) and Sebastiscus tertius (Barsukov et Chen); and Kudoa tumidisporica sp. n. in Photopectoralis bindus (Valenciennes) (type host) and Nuchequula nuchalis (Temminck et Schlegel). This study provides new data on multivalvulidan diversity in the ocean ecosystem.

Kudoa tanakai n. sp. (Myxozoa: Myxosporea: Multivalvulida), a new kudoid species with spheroid myxospores from the scalpel sawtail (Actinopterygii: Prionurus scalparum) from western Japan

We describe a new kudoid species, Kudoa tanakai n. sp., in the scalpel sawfish, Prionurus scalprum (Actinopterygii: Acanthuriformes: Acanthuridae), from the natural water around western Japan. The plasmodia were filamentous, localized in pseudocysts in the myofibers of the trunk muscles. The occurrence of plasmodia in the trunk muscle showed no site preference. Its myxospores were spheroid, measuring 6.6-7.6 (7.0) µm by 5.8-6.9 (6.3) µm in apical view (width) and 5.7-6.6 (6.2) in length (n = 30), with four shell valves and a corresponding number of spheroid polar capsules. Shell valves lacked apical protrusions, but scanning electron microscopy revealed that one of the four shell valves had two semi-lunar flaps at its apical terminus. Nucleotide sequencing of the small and large subunit ribosomal RNA genes of the present isolate showed phylogenetic affinities to kudoid species characterized by spheroid myxospores, such as K. musculoliquefaciens, K. hemiscylli, and K. carcharhini, but was molecularly and morphometrically distinct from these and other kudoid species. For direct comparison, Kudoa hemiscylli was collected from the Pacific spadenose shark, Scoliodon macrorhynchos (Elasmobranchii: Carcharhiniformes: Carcharhinidae), in the South China Sea off Guangdong Province, China, and the myxospore surface of the species was observed using scanning electron microscopy. Our study describes the new host and distribution record of this kudoid species originally described from a variety of elasmobranchs in the Australian Coral Sea.

Myxosporeans of the genus Kudoa (localization in the fish body, the form of spores and ways of their entry into the environment and into new hosts)

The purpose of the research is to study the localization of myxosporeans of the genus Kudoa Meglitsch, 1947 in body fish and possible ways for them to master organs and tissues in the process of evolution, the form of spores associated with localization, as well as the ways of their release into the environment and getting into new hosts.Materials and methods. The work is based on our own materials on fish myxosporeans from the Black, Azov and Mediterranean seas, as well as the Atlantic, Indian and Pacific oceans, collected in 1987–2021. In total, we have studied more than 12,000 sp. more than 100 species of fish. We also analyzed descriptions of 126 species of myxosporeans of the genus Kudoa, known in the world scientific literature until 2021 inclusive. For this, 450 domestic and foreign works have been worked out. The material was collected by the method of incomplete parasitological dissections. Smears made from tissues were processed according to the generally accepted method with the manufacture of permanent preparations. All measurements were made according to the standard method. To assess the number of parasites, standard indicators were used: the extensiveness and intensity of infection.Results and discussion. In total, we studied 19 species of myxosporeans of the genus Kudoa and 8 species of Kudoa spp. Six species (K. stellula, K. niluferi, K. anatolica from the Black Sea, K. unicapsula from the Mediterranean Sea, K. borimiri and K. igori from the South China (or East) Sea) were new to science. We have established 24 places of parasitism of myxosporeans of this genus in the body of fish. 83 species (66%, or 2/3 species) are found in muscles, sometimes affecting (8 species) other tissues and organs of the host. 43 species (34%, or 1/3 species) of representatives of the genus Kudoa are never found in muscle tissue. The primary sites of parasitism of myxosporeans of the genus Kudoa were probably the intestinal wall and gallbladder, then the parasites mastered other internal organs of fish and, ultimately, brain and muscle. The hypothetical ways of getting spores into the external environment and into new hosts are indicated. It is assumed that the most ancient forms are bivalve Kudoa, parasitizing in the gallbladder, four-valve Kudoa of an unusual shape, resembling representatives of other genera and parasitizing mainly in internal organs, as well as four-valve Kudoa with a classical square spore shape, rounded valve tops, with four equal polar capsules and the smallest sizes. Spores with a pointed stellate shape (only muscular forms) and spores with five or more valves and polar capsules (occurring in muscle and brain and having a larger size) should be considered to have arisen at a later time. The ways of getting spores into the environment and into new hosts are highlighted.

Four carangid fish species as new host records for Kudoa trachuri Matsukane, Sato, Tanaka, Kamata et Sugita-Konishi, 2011 (Myxozoa: Multivalvulida), and description of a new species, Kudoa longichorda sp. n., forming pseudocysts in the muscle of Decapterus tabl Berry

Multivalvulid myxosporeans of the genera Kudoa Meglitsch, 1947 and Unicapsula Davis, 1924 (Cnidaria: Myxozoa) are often the cause of unsightly cyst formation or postmortem myoliquefaction in the trunk muscle of commercial marine fish, which reduces the market value of infected individuals. Twenty species (18 Kudoa spp. and two Unicapsula spp.) have been recorded from carangid fish, although the majority of them, excluding polyxenous species, such as K. amamiensis Egusa et Nakajima, 1980, K. iwatai Egusa et Shiomitsu, 1983, K. nova Naidenova, 1975, K. quadratum (Thélohan, 1895) and K. yasunagai (Hsieh et Chen, 1984), are limited to a single or a few fish species. We report the occurrence of macroscopic cysts of Kudoa trachuri Matsukane, Sato, Tanaka, Kamata et Sugita-Konishi, 2011 in the trunk muscle of four new host fish species, i.e., Pseudocaranx dentex (Bloch et Schneider), Decapterus akaadsi Abe, D. muroadsi (Temminck et Schlegel) and Decapterus tabl Berry, fished from the Philippine Sea (Northwest Pacific Ocean), off southwestern of Japan. Myxospore morphology and genetic characteristics of the ribosomal RNA gene (rDNA) of these isolates were consistent with previous records of K. trachuri from Trachurus japonicus (Temminck et Schlegel) from around Japan. In addition, a new species of Kudoa that forms long filamentous pseudocysts in trunk myofibres was found in four of the six D. tabl collected in this study. We describe Kudoa longichorda sp. n. for this new isolate, based on its morphology of subquadrate myxospores with four shell valves and polar capsules and with small dimensions (length 4.3-5.5 µm, width 6.0-6.8 µm, thickness 4.8-6.3 µm, polar capsule length 2.3-3.1 µm, polar capsule width 1.1-1.7 µm), as well as 18S and 28S rDNA sequences distinct from those of known species.

Multivalvulidan myxosporeans from marine fishes in Nha Trang Bay, Vietnam, with descriptions of Kudoa igori n. sp. and Kudoa borimiri n. sp. from mullets

In March and April 2018, we carried out a survey of myxosporean parasites in coastal fishes collected from Nha Trang Bay in Vietnam's East Sea. Of the 159 fish specimens, 18 fish species were represented, belonging to 10 families. In 8 host species, 7 myxosporean species were found, representing the genera Kudoa and Unicapsula. Two of these species were new to science: Kudoa igori n. sp. from the gallbladder of Longarm mullet Osteomugil cunnesius (Valenciennes, 1836) (prevalence 10%) and Kudoa borimiri n. sp. from skeletal muscles of Longarm mullet and Longfinned mullet Osteomugil perusii (Valenciennes, 1836) (prevalence 30% and 60%, respectively). Vegetative stages were not found. Spores of K. igori n. sp. were small, orbicular to quadrate in apical view, and with four equal valves. In lateral view, spores were shallowly ovoid with a slightly protruding anterior pole. The 4 polar capsules were slightly unequal sizes and were oriented toward the apex of the spore. Dimensions were as follows: spore length 4.56 ± 0.22 (4.18-4.56), thickness 4.42 ± 0.39 (3.55-5.13), width 5.74 ± 0.46 (4.66-6.50), length of biggest polar capsule 1.38 ± 0.14 (1.1-1.65), middle 1.28 ± 0.12 (1.03-1.53), smallest 1.13 ± 0.11 (0.94-1.30), width of biggest polar capsule 1.03 ± 0.14 (0.83-1.4), middle 0.92 ± 0.12 (0.76-1.08), smallest 0.74 ± 0.12 (0.55-0.94). Spores of K. borimiri n. sp. had four equal valves with slightly rounded ends and were quadrate in apical view. In lateral view, spores were broadly deltoid. Four equal-sized polar capsules opened at the apex of the spore. In O. cunnesius, spore dimensions were as follows: length 3.51 ± 0.15 (3.34-3.92), thickness 3.65 ± 0.38 (2.79-4.21), width 4.97 ± 0.37 (4.13-5.97), length of the polar capsules 1.23 ± 0.18 (0.99-1.57), width 0.88 ± 0.07 (0.70-1.00). Overlapping dimensions for K. borimiri n. sp. spores were also found in O. perusii. Other known myxozoan species we encountered were Kudoa thyrsites and Kudoa whippsi, which had not previously been reported from the East Sea and Vietnam. We also encountered Kudoa monodactyli, which had not previously been reported from Nha Trang Bay. In addition, we report 2 additional species, a Kudoa sp. and a Unicapsula sp., that were not attributable to previously described myxozoans and need further investigation to completely characterize.

Kudoa hypoepicardialis and associated cardiac lesions in invasive red lionfish Pterois volitans in Grenada, West Indies

Invasive red lionfish Pterois volitans (Linnaeus, 1758) represent an ongoing ecological threat within temperate and tropical waters. Relatively little is known regarding the overall health of P. volitans and their potential for spreading pathogens in non-native regions. Lionfish collected from inshore reefs of Grenada, West Indies, in 2019 and 2021 were identified as P. volitans based on cytochrome c oxidase subunit 1 barcoding. Gross and microscopic examination of tissues revealed myxozoan plasmodia in the hearts of 24/76 (31.6%) lionfish by histopathology or wet mount cytology. Further histopathologic examination revealed severe granulomatous inflammation and myofiber necrosis associated with developing plasmodia and presporogonic life stages. Fresh myxospores were morphologically and molecularly consistent with Kudoa hypoepicardialis, being quadrate in apical view with 4 valves and 4 equal polar capsules. The spore body was 5.1-7.9 (mean: 6.0) µm long, 8.1-9.8 (8.7) µm wide, and 6.9-8.5 (7.7) µm thick. Polar capsules were 2.3-2.7 (2.5) µm long and 0.9-1.6 (1.3) µm wide. 18S small subunit rDNA sequences were 99.81-99.87% similar to sequence data from the original description of the species. Novel 28S large subunit rDNA and elongation factor 2 data, which did not match any previously reported species, were provided. This is the first account of a myxozoan parasite of P. volitans, a new host record and locality for K. hypoepicardialis, and one of few reports describing pathogen-associated lesions in invasive lionfish.

Descriptions of Three New Species and New Host or Distribution Records of Five Species of the Genus Kudoa (Myxozoa: Myxosporea: Multivalvulida) in Commercial Fishes Collected from South China Sea

PURPOSE

Myxosporeans of the genera Kudoa and Unicapsula (Cnidaria: Myxozoa: Myxosporea: Multivalvulida) may be causative agents of diseases that substantially lower the commercial value of certain marine fishes; thus, species identification is important to effectively manage outbreaks and control infections.

METHODS AND RESULTS

Our investigations of commercial fishes in the families Leiognathidae (three species), Ambassidae (one), Carangidae (five) and Gerreidae (one) in the South China Sea revealed new host records for Kudoa lutjanus (Ambassis martanus, and Gerres limbattus), Kudoa trachuri (Decapterus maruadsi, and Decapterus macrosoma), Kudoa uncinata (Photopectoralis bindus), and Kudoa longichorda (D. macrosoma) and new geographical distribution records for Kudoa javanensis (Alepes djedaba), K. trachuri, and K. longichorda. Moreover, three new Kudoa spp. were described based on detected specimens forming pseudocysts in trunk muscle myofibres. These included Kudoa corniculata n. sp. from Eubleekeria jonesi, and Leiognathus equulus; Kudoa hirsuta n. sp. from Trachurus japonicas, D. maruadsi, and D. macrosoma; and Kudoa parvibulvosa n. sp. from Megalaspis cordyla. To identify these species, their myxospores were morphologically and molecularly characterised based on the small and large subunits of their ribosomal RNA genes.

CONCLUSIONS

In this study, we demonstrated morphometric variations in the myxospores of various species and an atypical K. uncinata morphotype with unequal polar capsules. Hence, taxonomic identification of myxosporeans require molecular characterisation.

Morphological Characterization and Molecular Phylogenetic Analysis of Kudoa iwatai from Large Yellow Croaker (Larimichthys crocea) as a New Host in China

Simple Summary

Larimichthys crocea is the most important economic marine cultured fish in China. Kudoa parasites are critical pathogens that infect a wide range of marine and freshwater fish. Compared to the hundred marine Kudoa species recognized in wild and cultured fish worldwide, records of Kudoa are relatively few in China. In this report, large yellow croakers were found to be infected with Kudoa for the first time in China. Morphological observations and molecular techniques were combined for the final identification of Kudoa iwatai. Additionally, the morphological characterization and phylogenetic status of Kudoa iwatai have been described in detail. This study enriches knowledge about Kudoa iwatai and provides a direction for early disease prevention and monitoring of large yellow croakers.

Abstract

Kudoa (Myxosporea: Multivalvulida) parasites are critical pathogens in marine and freshwater fish associated with significant economic losses and reduced market prices caused by post-mortem myoliquefaction or numerous cysts on muscles. In the present study, large yellow croakers infected by Kudoa were found during fish disease surveillance in China in November 2020 and used for morphological observation and characterization using light DIC microscopy and electron microscopy. Numerous creamy-white oval plasmodia were observed in muscles and on the surface of brain cartilage, gill arches, and serosal surfaces. The spores were considerably longer and thicker than previously reported Kudoa, with protruding polar filaments (PFs) in the mature spores, fingertip-shaped apical projections (APs), and polar capsules. Phylogenetic analyses with SSU rDNA, LSU rDNA, and mitochondrial DNA showed that the Kudoa-infected sample (LcK-2020) had the highest similarity to Kudoa iwatai reported in Japan. Based on the morphological characterization and phylogenetic analysis, it could be concluded that the sample LcK-2020 was infected by Kudoa iwatai, which would be the first report of Kudoa iwatai infection in large yellow croaker in China.

Occurrence of Kudoa prunusi and K. lateolabracis (Myxozoa: Myxosporea: Multivalvulida) in Philippine-Sea Japanese parrotfish (Calotomus japonicus)

Multiple Kudoa spp. (Myxozoa: Myxosporea: Multivalvulida) have been recorded in Japanese parrotfish (Calotomus japonicus) from the Philippine Sea (Northwest Pacific Ocean), off southwestern Japan; Kudoa yasunagai in the brain, and K. igami, K. lateolabracis, and K. thalassomi in the muscles. This study examined eight Philippine Sea Japanese parrotfish samples collected in January and February 2019 and found K. prunusi in the brain (3-57 plasmodia/fish; average 17.9) and K. lateolabracis plasmodia in the trunk muscle of all fish individuals examined. The K. prunusi in this study was characterized by myxospores predominatetly with six shell valves (SVs) and a corresponding number of polar capsules (PCs), contrasting with the original description of the species from farmed Pacific bluefin tuna (Thunnus orientalis) brain that characterized the species as having predominately five SVs/PCs. Molecular-genetic characterization of 18S and 28S ribosomal RNA genes and mitochondrial DNA genes (cytochrome c oxidase subunit 1 and small and large ribosomal RNA subunits) clearly differentiated the K. prunusi isolate from K. yasunagai, commonly characterized by six or seven, but rarely five, SVs/PCs myxospores. The Japanese parrotfish is a new host record for K. prunusi and speculated to be an important reservoir host in its natural waters. Kudoa lateolabracis myxospores isolated from pseudocysts in the myofiber were morphologically and phylogenetically close to a clade of the Kudoa spp. that exhibit cruciform myxospores similar to K. thyrsites. This study is the first to sequence a mitochondrial DNA of small and large subunit ribosomal RNA of K. lateolabracis.

Identification of a new species, Unicapsula aequilobata n. sp., and Unicapsula seriolae (Myxozoa: Myxosporea: Multivalvulida) in carangid fish from the South China Sea

An examination of 18 fishes caught in the South China Sea detected two Unicapsula spp. in the myofibers of the trunk muscles of carangid fishes: Unicapsula aequilobata n. sp. in the Japanese scad, Decapterus maruadsi, and Unicapsula seriolae in the yellowstripe scad, Selaroides leptolepis. They formed thin filamentous pseudocysts of 0.9-2.0 (mean 1.4) mm by 0.03-0.06 (0.04) mm (n = 5) and 0.9-3.4 (2.1) mm by 0.02-0.05 (0.04) mm (n = 12), respectively. Myxospores of U. aequilobata n. sp. are composed of three equal shell valves and measured 6.7-8.5 (7.3) μm in length and 7.1-8.8 (7.6) μm in width, and contained a prominent polar capsule (PC) 3.2-3.8 (3.6) μm in diameter (n = 18) and two rudimentary PCs. A nucleotide sequence (5127 bp) of the ribosomal RNA gene (rDNA) array was obtained for the genetic characterization of this new species. Based on morphological and phylogenetic criteria, we erect U. aequilobata n. sp. as the sixteenth species in the genus Unicapsula. Nucleotide sequences of the 18S and 28S rDNA obtained from U. seriolae from the yellowstripe scad were almost identical (99.6-100% or 99.0-99.6%, respectively) to those from fish found in the seawaters around Australia and Japan. Consequently, this is a new host and geographical distribution records for U. seriolae. In addition, we illustrated the predicted secondary structure of the available 5.8S rDNA sequences of multivalvulid species, including those obtained from U. aequilobata n. sp., to assess the significance of interspecific nucleotide variations in this short rDNA unit.

First report of three multivalvulid species (Cnidaria: Myxozoa: Myxosporea) in commercial fishes from Java Sea, Indonesia, with records of Unicapsula pyramidata and two new Kudoa spp

Commercial marine fishes caught locally in East Java, Indonesia, were examined for multivalvulid myxosporeans (Cnidaria: Myxozoa: Myxosporea). Plasmodia of Unicapsula pyramidata were detected in the trunk muscle of two fork-tailed threadfin breams (Nemipterus furcosus). Genetic comparisons of this sample to those collected in the Australian Coral Sea and South China Sea showed few nucleotide substitutions in the small subunit and large subunit ribosomal RNA gene (rDNA) with the species isolated in the Australian Coral Sea and South China Sea. Pseudocysts of two new Kudoa spp. with four shell valves and polar capsules were found in the trunk muscle of two shrimp scads Alepes djedaba and two flathead grey mullets Mugil cephalus. Kudoa javaensis n. sp. myxospores isolated from the shrimp scad were 5.1-7.2 (mean 6.2) μm thick, 6.2-7.9 (7.3) μm wide, and 4.6-6.3 (5.4) μm long, with polar capsules 1.9-2.5 (2.2) μm long and 1.1-1.4 (1.3) μm wide (n = 15). Kudoa surabayaensis n. sp. myxospores isolated from the flathead grey mullet were 5.8-6.7 (6.3) μm thick, 6.4-7.6 (6.9) μm wide, and 4.6-5.0 (4.7) μm long, with polar capsules 1.8-2.4 (2.1) μm long and 0.9-1.3 (1.1) μm wide (n = 25). These two Kudoa spp. showed critical differences in spore shapes (semiquadrate with unequal shell valves vs. equal shell valves), and absence vs. presence of uplifted shell valve termini. Nucleotide sequencing of rDNA supported the morphological differentiation of these two species. Furthermore, these two isolates were morphologically and phylogenetically distinct from any recorded Kudoa spp.

Identification of four new Kudoa spp. (Myxozoa: Myxosporea: Multivalvulida) in commercial fishes collected from South China Sea, Atlantic Ocean, and Bering Sea by integrated taxonomic approach

Members of the myxosporean genus Kudoa are defined as having a myxospore with four or more shell valves (SVs) and a corresponding number of polar capsules (PCs). Here, we employed integrated taxonomic approaches to four kudoid isolates from Acentrogobius chlorostigmatoides and Konosirus punctatus from the South China Sea, off Guangdong, Pentanemus quinquarius from the Southeast Atlantic Ocean, off West African coast, and Atheresthes stomias from the Bering Sea, off Alaska, and concluded that all these kudoids were novel species, named Kudoa acentrogobia n. sp., Kudoa guangdongensis n. sp., Kudoa iidae n. sp., and Kudoa aburakarei n. sp., respectively. Kudoa guangdongensis n. sp., forming pseudocysts in the trunk muscle myofibers of K. punctatus, had large-sized tripod myxospores with three wing-like SV extensions and three PCs (one prominent PC and two rudimentary PCs). Phylogenetic analyses based on the 18S and 28S ribosomal RNA gene (rDNA) demonstrated its affinity to the genus Kudoa, not to Unicapsula characterized by a myxospore with one prominent PC and two rudimentary PCs, suggesting the atypical nature of this new species in the context of myxospore morphology. Three other kudoid isolates had four SVs and PCs in a semi-quadrated, ray-like, or cruciform myxospore, respectively, forming pseudocysts in the trunk muscle myofibers. Kudoa iidae n. sp. forming pseudocysts in the muscles of P. quinquarius from Southeast Atlantic Ocean had unique myxospores with ray-like form, showing close morphological resemblance to Kudoa rayformis, which were recorded from the muscle of Scomberomorus sierra from the Pacific Ocean off Panama. These two species had a phylogenetic relationship of morphological convergence, evolving separately in different sea areas. It is fairly difficult to differentiate K. acentrogobia n. sp. and K. aburakarei n. sp., prevalent in their host fishes, from kudoid species with similar myxospore morphology (e.g., Kudoa nova and Kudoa thyrsites, respectively), but distinct in phylogeny from known Kudoa spp. Combined taxonomic identification of multivalvulid myxosporeans based on both morphological criteria of isolated myxozoans and their molecular characterization could disclose their real biodiversity and phylogeny.