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

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.

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.

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.

High-Throughput Sequencing of Environmental DNA as a Tool for Monitoring Eukaryotic Communities and Potential Pathogens in a Coastal Upwelling Ecosystem

The marine environment includes diverse microeukaryotic organisms that play important functional roles in the ecosystem. With molecular approaches, eukaryotic taxonomy has been improved, complementing classical analysis. In this study, DNA metabarcoding was performed to describe putative pathogenic eukaryotic microorganisms in sediment and marine water fractions collected in Galicia (NW Spain) from 2016 to 2018. The composition of eukaryotic communities was distinct between sediment and water fractions. Protists were the most diverse group, with the clade TSAR (Stramenopiles, Alveolata, Rhizaria, and Telonemida) as the primary representative organisms in the environment. Harmful algae and invasive species were frequently detected. Potential pathogens, invasive pathogenic organisms as well as the causative agents of harmful phytoplanktonic blooms were identified in this marine ecosystem. Most of the identified pathogens have a crucial impact on the aquacultural sector or affect to relevant species in the marine ecosystem, such as diatoms. Moreover, pathogens with medical and veterinary importance worldwide were also found, as well as pathogens that affect diatoms. The evaluation of the health of a marine ecosystem that directly affects the aquacultural sector with a zoonotic concern was performed with the metabarcoding assay.

Utrastructure and molecular phylogeny of the myxozoan Kudoa ocellatus n. sp. (Myxozoa: Kudoidae), a parasite of the Oscar, Astronotus ocellatus (Agassiz, 1831; Teleostei: Cichlidae), a fish from northern Brazil

Kudoa ocellatus n. sp. was found in the musculature of Astronotus ocelattus (Agassiz, 1831) from the Arari River on Marajó Island in Pará, Brazil. The new species forms pseudocysts in the epaxial and hypaxial musculature composed of various spores that are pseudoquadrate in the apical view. In the lateral view, the spores were triangular or pyramidal. In the lateral view, the spores were 46 ± 0.11 μm (4.5-4.8) in length and 6.6 ± 0.3 μm (6.2-7.2) in width, with four pyriform polar capsules of equal size that measured 2.0 ± 0.16 μm (1.8-2.2) in length and 1.5 ± 0.18 μm (1.3-1.8) in width. Based on the partial (1418 bps) sequence of the SSU rDNA gene, Kudoa ocellatus n. sp. was distinct from all the other Kudoa species deposited in GenBank. The phylogenetic Bayesian Inference and P distance placed the new species together with the other Kudoa species that parasitize freshwater Amazonian fish. The morphological evidence, together with the SSU rDNA gene sequence, supported the description of Kudoa ocellatus n. sp., a distinct new species of the genus, which parasitizes a freshwater Amazonian cichlid.

First report of Kudoa thunni and Kudoa musculoliquefaciens affecting the quality of commercially harvested yellowfin tuna and broadbill swordfish in Eastern Australia

Recent anecdotal reports from seafood processors in eastern Australia have described an increased occurrence of post-mortem myoliquefaction ('jellymeat') in broadbill swordfish Xiphias gladius, and macroscopic cysts throughout the musculature of yellowfin tuna Thunnus albacares. A genus of parasitic cnidarians, Kudoa (Myxosporea, Multivalvulida), species of which are known to occur in economically important wild-caught fish species globally, can cause similar quality-deterioration issues. However, Kudoa sp. epizootiology within commercially harvested, high-value fish caught within Australia is poorly understood, despite the parasite's economic importance. To determine the causative agent responsible for the observed quality deterioration in swordfish and yellowfin tuna, muscle-tissue samples from seafood processors in Mooloolaba, Australia, collected from October 2019-February 2020, were examined for parasitic infection. Kudoid myxospores were identified from both hosts and were subquadrate in shape, with four equal-sized polar capsules. The SSU rDNA sequences from both fish shared > 99% identity to Kudoa species. Kudoa musculoliquefaciens was isolated from 87.1% of swordfish sampled, suggesting that it is a widespread parasite in swordfish from the southwest Pacific Ocean. This study provides the first molecular and morphological characterisation of Kudoa thunni in yellowfin tuna and K. musculoliquefaciens in swordfish harvested from the waters of eastern Australia, expanding the geographical distribution of K. thunni and K. musculoliquefaciens to include the Coral and Tasman Seas. We demonstrate that not all infected swordfish progress to jellymeat, show the usefulness of molecular tools for reliably identifying infection by Kudoa spp., and add to the overall knowledge of kudoid epizootiology in wild-caught fish.

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.