(Myxozoa: Multivalvulida) from the brain of Pacific bluefin tuna Thunnus orientalis (Temminck & Schlegel, 1844) cultured in Japan

First report of Kudoa species (Myxozoa, Multivalvulida) infection in purple-spotted Bigeye (Priacanthus tayenus) from the Saudi Arabian Gulf

The purple-spotted bigeye, Priacanthus tayenus, is a marine benthic fish native to the Indian and Pacific Oceans, including the Arabian Gulf in Saudi Arabia. This study identified a myxozoan parasite infecting wild P. tayenus from the Saudi Arabian Gulf. These parasites produced spherical to ovoid-shaped, white plasmodia enclosed within pseudocysts in the fish musculature. The annual infection rate was 5.1%, with the highest prevalence in summer (7.6%), followed by spring (6%), and autumn (2.5%), while no infections were observed in winter. The number of plasmodia per fish ranged from 100 to 150 (135.1 ± 16.2). Their dimensions were 4-4.7 mm (4.3 ± 0.3 mm) in length and 4.5-7 mm (6 ± 1.1 mm) in width. Milky-colored exudates within the plasmodia contained mature spores measuring 8-9 μm (8.6 ± 0.4 μm) x 6-7.5 μm (6.9 ± 0.5 μm). The polar capsules of the spores exhibited dimensions of 2-5 μm (3.5 ± 0.5 μm) x 2.5-4.5 μm (3 ± 0.45 μm). Both morphological and genetic analyses confirmed these plasmodia as a novel Kudoa species. Histopathological examination revealed atrophy in the surrounding muscles without an inflammatory response. This study documents the first occurrence of a novel Kudoa sp. in P. tayenus at the Jubail landing site in Saudi Arabia, emphasizing the need for further surveillance and investigations to elucidate its pathogenesis and implications for wild fish stocks.

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.

Kudoa rousseauxii n. sp. (Cnidaria: Multivalvulida) Infects the Skeletal Muscles of the Freshwater Fish Brachyplatystoma rousseauxii in the Amazon River

PURPOSE

Members of the genus Kudoa Meglitsch, 1947 are known to infect the muscles of commercially important fishes worldwide, including those in the order Siluriformes. This paper describes the occurrence of a new species of Kudoa in the catfish Brachyplatystoma rousseauxii based on morphological study and molecular analysis of the ribosomal RNA gene (SSU rDNA).

METHODS

Fifteen specimens of Brachyplatystoma rousseauxii were purchased from fishing zones near Mosqueiro Island, Belém, Pará, Brazil. After necropsy, tissue samples and cysts were analyzed using a stereomicroscope, and fresh slides were viewed under a light microscope to confirm parasitic infection. The tissue fragments were removed and processed for molecular and histological analyses.

RESULTS

Microscopic pseudocysts were found in the epaxial region of skeletal muscle fibers in 80% of the analyzed specimens. The myxospores were quadrangular with four shell valves (SV), pyriform polar capsules (PC), and internal symmetry. Phylogenetic analyses indicated that the new species formed a cluster with the species previously described in the Amazon, being close to two freshwater species.

CONCLUSIONS

Morphological differences and molecular data of SSU rDNA support that Kudoa rousseauxii n. sp. is a new species that infects B. rousseauxii, a freshwater fish with intense migratory cycles that is widely captured and consumed in the Amazon.

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.

Detection and characterization of Kudoa thunni from uncooked yellowfin tuna (Thunnus albacares) in Southeast Asia

Myxosporean parasites Kudoa spp. have been reported in several marine fish species worldwide. However, little is known about the contamination of these parasites in raw fish in Southeast Asia, where the consumption demand of uncooked fish is increasing. In 2019, the occurrence of several cases of raw yellowfin tuna (Thunnus albacares) obtained from retail shops with the presence of unknown white, nodular cysts within the musculature have raised public health concerns for the consumption of raw marine fish in Vietnam. Microscopic examination revealed numerous myxospores with the quadratic shape of the Kudoidae. Morphologically, stained spores detected in this study are suspected to Kudoa thunni. To confirm the suspected Kudoa species, further examination of the 18S small-subunit (SSU) was conducted and the results of nucleotide sequence analysis obtained from nodular cysts revealed 99.18-100% identity to that of Kudoa thunni sequences available in GenBank. Detection of K. thunni infection in tuna in Southeast Asia highlights the need for appropriate surveillance and control measures to ensure high quality standards and safety on raw fish production and consumption.

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.

Myxobolus freitasi n. sp. (Myxozoa: Bivalvulida), a parasite of the brain of the electric knifefish in the Brazilian Amazon region

A total of 30 specimens of the Amazonian electric knifefish, Brachyhypopomus beebei Schultz, 1944 (Gymnotiformes: Hypopomidae), were collected from the Peixe-Boi River in the state of Pará, Brazil (1°06'59" S; 47°18'26" W). Fragments of the brain tissue were extracted for analysis via optical microscopy, and 18 specimens (60%) presented microparasites of the genus Myxobolus, with unequal capsules. The spores were 18.6 µm (17.7-19.8 µm) long and 8.6 µm (8.4-9.0 µm) wide; the largest polar capsule was 13.0 µm (12.4-13.4 µm) long and 5.6 µm (5.3-6.0 µm) wide, and the smallest capsule was 5.0 µm (4.5-5.3 µm) long and 2.5 µm (2.3-2.6 µm) wide. Infected brain fragments were extracted for histological processing and staining with hematoxylin-eosin and Ziehl-Neelsen. Some fragments were conserved in ethanol for molecular genetics analysis. A partial sequence of the 18S DNA gene was obtained from the spores, which did not correspond to any other sequences deposited in GenBank, although it did form a clade with other Myxobolus parasites of the nervous system. The morphological data, together with molecular phylogeny, supported the designation of a new species Myxobolus freitasi n. sp.

Survey of Kudoa spp. (Myxozoa, Cnidaria) in fishes from the Madeira Archipelago and the Portuguese mainland coast: detection of Kudoa thyrsites in new hosts Scomber colias and Micromesistius poutassou

Myxozoan parasites of the genus Kudoa Meglitsch, 1947 are associated with post-mortem tissue degradation that causes great financial losses to commercial fisheries. Kudoa thyrsites (Gilchrist, 1924) is a species with a very wide host range including commercial tunas, mackerels, salmonids and flatfishes. A sample of 190 fishes of 18 species from the Madeira Archipelago and 30 Atlantic chub mackerel, Scomber colias Gmelin, and 30 blue whiting, Micromesistius poutassou (Risso), from the Portuguese mainland coast were examined for the presence of species of Kudoa. The prevalence of Kudoa spp. was 80% in M. poutassou and 60% in S. colias. No spore was detected in S. colias from Madeira, which was confirmed by specific PCR screening of the muscle from all individuals of S. colias. SSU rDNA analysis revealed that M. poutassou and S. colias from the Portuguese mainland coast were infected with K. thyrsites, an economically important myxozoan parasite. Both sequences were identical with sequences of the eastern Atlantic K. thyrsites genotype, including that from the type host of this parasite. This is the first report of K. thyrsites from M. poutassou and S. colias. The fact that spores of species of Kudoa were not detected in fishes screened in the Madeira Archipelago may be explained by various ecological factors, such as the absence of a continental shelf, a short insular shelf, and oceanic waters with low productivity, all resulting in reduced abundance of benthic organisms. Consequently, it is possible that as yet unknown annelid definitive hosts of Kudoa spp. are absent or very rare near Madeiran coasts.

Simultaneous occurrence of two new myxosporean species infecting the central nervous system of Hypopygus lepturus from Brazil

This paper describes 2 new myxosporean species, Henneguya lepturus sp. nov. and Thelohanellus lepturus sp. nov., simultaneously infecting the brain and spinal cord of Hypopygus lepturus Hoedeman, 1962 (Teleostei, Hypopomidae) from the Brazilian Amazon (Roraima State). Several spherical cysts of varying dimensions (up to 135 µm) were microscopically observed. The myxospores of H. lepturus sp. nov. measured 25.8 µm in total length, having an ellipsoidal body (12.4 × 6.4 × 2.2 µm) and 2 equal tapering tails (13.4 µm in length). Each of the 2 pyriform polar capsules measured 4.4 × 1.6 µm and possessed a polar filament coiled in 8-9 turns. The myxospores of T. lepturus sp. nov. were pyriform, formed by 2 equal valves (17.7 × 9.1 × 4.3 µm) surrounding a single polar capsule (10.9 × 3.5 µm) that had a coiled polar filament with 13-16 turns and a binucleated sporoplasm that contained several circular sporoplasmosomes. Molecular analysis of the small subunit (SSU) rRNA gene sequences of these 2 species were in agreement with the taxonomic classification derived from the ultrastructure of the myxospores. Histopathology of the host tissue showed degradation of the myelinated axons surrounding the cysts of both species, with the hosts displaying behavioural changes and erratic movements when observed in an aquarium.

Infection of the muscle tissue of the filter-feeding cichlid, Chaetobranchopsis orbicularis Steindachner, 1875, by Kudoa orbicularis (Myxozoa: Multivalvulidae) on Marajó Island in the Brazilian Amazon region

ABSTRACT This study describes aspects of infections caused by the myxosporidian Kudoa orbicularis in filter-feeding cichlids, Chaetobranchopsis orbicularis, caught in the Arari River in the municipality of Cachoeira do Arari, on Marajó Island, Pará, Brazil. The parasite forms pseudocysts scattered throughout the striated epaxial and hypaxial muscles. Samples embedded in paraffin were analyzed histologically using hematoxylin-eosin, Gömöri, Ziehl-Neelsen, and Giemsa staining. Necropsy of the C. orbicularis specimens revealed that 100% (50/50) were infected with K. orbicularis. The specimens presented grossly abnormal muscle texture, resulting in extensive inconsistencies and weakness. Progressive softening of the muscles was observed during necropsy, indicating the rapid enzymatic autolysis of the tissue. The parasite found in the muscle tissue of C. orbicularis was identified as K. orbicularis, with clinical signs of disease being observed in the fish. The necropsy revealed extensive damage to the host organism, with well-established fibrocystic infections in the muscle fibers, associated with post mortem myoliquefaction.

Incidence of three Kudoa spp., K. neothunni, K. hexapunctata, and K. thunni (Myxosporea: Multivalvulida), in Thunnus tunas distributed in the western Pacific Ocean

A variety of tunas of the genus Thunnus are consumed daily in Japan as sliced raw fish (sashimi and sushi). The consumption of fresh sliced raw fish, i.e., unfrozen or uncooked, can sometimes cause food poisoning that is manifested by transient diarrhea and vomiting for a single day. One of the causes of this type of food poisoning has been identified as live Kudoa septempunctata (Myxosporea: Multivalvulida) in the olive flounder (Paralichthys olivaceus). Furthermore, raw slices of fresh tunas are highly suspected to be a possible causative fish of similar food poisoning in Japan. In the present study, we conducted a survey of kudoid infections in tunas (the yellowfin tuna Thunnus albacares, the Pacific bluefin tuna Thunnus orientalis, and the longtail tuna Thunnus tonggol) fished in the western Pacific Ocean off Japan and several East Asian countries and characterized morphologically and genetically the kudoid myxospores in pseudocysts or cysts dispersed in the trunk muscles. Pseudocysts of solely Kudoa hexapunctata were identified in the Pacific bluefin tuna (four isolates), whereas in the yellowfin tuna (21 isolates) pseudocysts of Kudoa neothunni and K. hexapunctata were detected at a ratio of 15:6, respectively, in addition to cyst-forming Kudoa thunni in five yellowfin tunas. In the trunk muscles of six longtail tunas examined, pseudocysts of K. neothunni (all six fish) and K. hexapunctata (two fish) were densely dispersed. The myxospores of K. neothunni found in these longtail tunas had seven shell valves and polar capsules (SV/PC) instead of the more common six SV/PC arranged symmetrically. Nucleotide sequences of the 18S and 28S ribosomal RNA gene (rDNA), some with the internal transcribed spacer regions as well, of K. hexapunctata and K. neothunni from the three Thunnus spp., including the seven-SV/PC morphotype, were very similar to previously characterized nucleotide sequences of each species, whereas the 18S and 28S rDNA of four isolates of K. thunni from yellowfin tunas showed a range of nucleotide variations of 99.0-99.9% identity over 1752-1763-bp long partial 18S rDNA and 97.4-99.9% identity over 797-802-bp long partial 28S rDNA. Therefore, this rather high variation of the rDNA nucleotide sequences of K. thunni proved to be contrary to the few variations of K. neothunni and K. hexapunctata rDNA nucleotide sequences. The present study provides a new host record of the longtail tuna for K. neothunni and K. hexapunctata and reveals a high prevalence of the seven-SV/PC myxospore morphotype of K. neothunni in this tuna host.

Phylogenetic study of the genus Kudoa (Myxozoa: Multivalvulida) with a description of Kudoa rayformis sp. nov. from the trunk muscle of Pacific sierra Scomberomorus sierra

Kudoa rayformis n. sp. (Myxozoa; Multivalvulida) was observed in the trunk muscle of Pacific sierra Scomberomorus sierra caught off the coast of Tonosi, Panama. The species formed pseudocysts in myofibers and infection was subclinical. The myxospores possessed four polar capsules and spore valves, one of which had a distinct filamentous extension. This unique morphological characteristic of the myxospore validated this as a new species of Kudoa. Genetically, K. rayformis n. sp. is closest to K. inornata, with 98% and 91% similarity in 18S and 28S rDNA, respectively, but its spore shape was clearly distinct. The 18S rDNA and concatenated sequences from K. rayformis were used in molecular phylogenetic analyses of kudoids to examine the congruence of phylogeny with infection site tropism, spore morphology and cyst/pseudocyst formation. The results demonstrated that the phenotypic traits were correlated with the phylogeny of Kudoidae, and that the biological features of K. rayformis originated from the ancient Kudoidae as exhibited by the non-specific infection site tropism and the ability to infect muscle and form pseudocysts.

Detection rate of diarrhoea-causing Kudoa hexapunctata in Pacific bluefin tuna Thunnus orientalis from Japanese waters

Diffuse outbreaks of food poisoning with unknown aetiologies leading to diarrhoea and vomiting within a short time after ingesting flatfish (Paralichthys olivaceus), tuna (Thunnus spp.), or amberjack (Seriola dumerili) have occurred nationwide in Japan, including the Tokyo metropolitan area. In this study, we surveyed the detection rates of kudoid parasites in 12 tuna samples that caused clinical diarrhoea from 2009 to 2012; we assessed 104 samples of whole juvenile Pacific bluefin tuna (PBT, Thunnus orientalis) and 153 block samples of other tuna distributed in the Tokyo Metropolitan Central Wholesale Market. The survey revealed that more than 70% of clinical diarrhoea cases due to tuna ingestion occurred between June and September, and Kudoa hexapunctata were detected in 9 of 12 tuna samples associated with clinical diarrhoea cases. The numbers of spores and 18S ribosomal DNA (rDNA) copies per gram of fish in 8 of 9 samples were more than 1×10(6) spores and 1×10(9) copies, respectively. Market research revealed that the K. hexapunctata-positive rate in juvenile PBT from Japanese waters was 64.4% (67/104) but that in adult PBT was 10.4% (7/67). The numbers of K. hexapunctata 18S rDNA copies in 64.5% (20/31) samples and 72.7% (16/22) of <5kg fish samples collected between May and July were more than 1×10(9)copies/g. On the other hand, kudoid parasites were not detected from 73 tuna samples except for a single sample of Thunnus albacares. Cell monolayer permeability assays performed to examine the toxicity of K. hexapunctata against Caco-2 cells revealed that the transepithelial electrical resistance (TER) in 5×10(7)K. hexapunctata spores decreased by 80% within 2-4h. In conclusion, K. hexapunctata was commonly detected in juvenile PBT from Japanese waters and are a likely cause of the diarrhoea outbreaks.

Kudoa hexapunctata n. sp. (Myxozoa: Multivalvulida) from the somatic muscle of Pacific bluefin tuna Thunnus orientalis and re-description of K. neothunni in yellowfin tuna T. albacares

Since Kudoa septempunctata in olive flounder (Paralichthys olivaceus) was indicated to cause food poisoning in humans, other Kudoa species are suspected to have pathogenic potential. Recently, a myxosporean possibly associated with food poisoning in humans consuming raw Pacific bluefin tuna, Thunnus orientalis, was identified as Kudoa neothunni. This is a known causative myxosporean of post-harvest myoliquefaction in yellowfin tuna Thunnus albacares. Regardless of the significant differences in the 28S rDNA sequence and the pathological character (with/without myoliquefaction) between the two T. orientalis and T. albacares isolates, they were considered intraspecific variants of K. neothunni. However, the light and low-vacuum electron microscopic observations in the present study revealed that there were two morphotypes; pointed- and round-type spores, which were significantly differentiated by the ratio of suture width to spore width. Furthermore, the two morphotypes were genetically distinguishable by the 28S rDNA sequence analysis. This morphological and molecular evidence validates that the two Kudoa types are separate species, and thus the pointed- and round-types are referred to as K. neothunni and Kudoa hexapunctata n. sp., respectively. K. neothunni was detected solely from T. albacares, whereas K. hexapunctata n. sp. was found not only from T. orientalis but also from T. albacares.

First record of Unicapsula seriolae (Myxozoa: Multivalvulida) from the muscle of Malabar grouper Epinephelus malabaricus in Japan

Unicapsula seriolae (Myxozoa; Multivalvulida) was found in the trunk muscle of Malabar grouper Epinephelus malabaricus caught off Wakayama Prefecture, Japan. Numerous filamentous or sesamoid brown to black lesions were observed in the skeletal muscle. Histopathological observation indicated that the lesions were myxosporean plasmodia encapsulated by a fibrous layer, accompanied by melanin deposition. Spores having one large and two rudimentary polar capsules were subspherical in shape and 6.6 × 6.9 μm in size. Scanning electron microscopy revealed that spores were composed of three spore valves. Morphological characteristics were consistent with U. seriolae, which is reported to cause myoliquefaction in yellowtail kingfish Seriola lalandi in Australia. Molecular analysis of the SSU and LSU rDNA supported identification of the species as U. seriolae. This is the first report of Unicapsula in Japan.

Seasonal monitoring of Kudoa yasunagai from sea water and aquaculture water using quantitative PCR

Kudoid myxozoans pose serious chronic problems in marine fisheries by causing pathological damage to host fish, reducing the market value of infected fish and potentially threatening public health. Kudoa yasunagai is a cosmopolitan parasite that infects the brains of various marine fishes, including important aquaculture species. We developed a quantitative PCR assay to detect K. yasunagai in sea water, and we used it to monitor abundance of the parasite in the environment and in culture through spring and winter. Quantitative PCR detected K. yasunagai DNA from sea water, with the lowest reliable threshold of 162 copies 28S rDNA l-1. Parasite DNA was detected sporadically in sea water throughout the study period of May through December 2012. The highest level of detected DNA occurred in mid-December (winter), at 117180 copies-equivalent to an estimate of over 200 myxospores l-1. Parasite DNA was generally not detected in August or September, the period with the highest water temperature. The reason for this observation is unknown, but the timing of parasite development may play a role. The amount of detected DNA was not different between unfiltered culture water and water filtered through a high-speed fiber filtration system. This result and the past incidence of high infection rate of fish reared in filtered water indicate that the mechanical removal of K. yasunagai from culture water is difficult. Detecting the precise onset and time window of infection in host fish will be an important step in the development of measures to control this economically important parasite.

Synopsis of the species of Kudoa Meglitsch, 1947 (Myxozoa: Myxosporea: Multivalvulida)

A synopsis of the species of Kudoa Meglitsch, 1947 (Myxozoa, Myxosporea, Multivalvulida) is presented, including 95 nominal species. For each species the most relevant morphological and morphometric features are indicated in tabulated format. Included are data on the site of infection within the host, the type-host and type-locality, plus a full bibliography of the original records for these species. Molecular data (GenBank accession numbers) are also provided whenever possible.

Kudoa thunni from blackfin tuna (Thunnus atlanticus) harvested off the island of St. Kitts, West Indies

Numerous myxozoan cysts (∼ 1 mm) were found in the musculature of blackfin tuna (Thunnus atlanticus) harvested off the Caribbean island of St. Kitts. Myxospores were consistent with quadrate members of the Kudoidae, measuring 8.8 (8.2-9.4) μm wide, 7.3 (6.6-8.3) μm thick, and 6.2 (5.8-6.9) μm long with 4 uniform drop-like polar capsules measuring 2.7 (2.2-3.2) μm long and 2.0 (1.7-2.2) μm wide. The 18S small-subunit (SSU) and 28S large-subunit (LSU) ribosomal DNA sequences did not result in direct matches to any published sequences. However, the SSU sequences (1,786 base pairs [bp]) obtained from 6 individual cysts were identical and demonstrated high homology to Kudoa thunni (99.0%) from albacore (Thunnus alalunga). Alternatively, 33 unique sequences were obtained for the LSU (∼ 800 bp), demonstrating 0.1 to 5.0% variability between them, although a majority of these sequences (60%) demonstrated high homology (>99%) to K. thunni. Morphologically, the case isolate was smaller than published descriptions of K. thunni; however, rDNA sequence homology, and phylogenetic placement based on concatenated SSU and LSU rDNA sequences suggests this case isolate and K. thunni are conspecific. To our knowledge this is the first report of K. thunni infection in blackfin tuna from the Caribbean.

Characterization of the ribosomal RNA gene of Kudoa neothunni (Myxosporea: Multivalvulida) in tunas (Thunnus spp.) and Kudoa scomberi n. sp. in a chub mackerel (Scomber japonicus)

Kudoa neothunni is the first described Kudoa species having six shell valves and polar capsules, previously assigned to the genus Hexacapsula Arai and Matsumoto, 1953. Since its genetic analyses remain to be conducted, the present study characterizes the ribosomal RNA gene (rDNA) using two isolates from a yellowfin tuna (Thunnus albacares) with post-harvest myoliquefaction and a northern bluefin tuna (Thunnus thynnus) without tissue degradation. Spores of the two isolates localized in the myofiber of trunk muscles, forming pseudocysts, and showed typical morphology of K. neothunni with six equal-sized shell valves radially arranged in apical view: spores (n = 15) measuring 9.5-11.4 μm in width, 7.3-8.6 μm in suture width, 8.9-10.9 μm in thickness, and 7.3-7.7 μm in length; and polar capsules measuring 3.6-4.1 μm by 1.8-2.3 μm. In lateral view, the spores were pyramidal in shape without apical protrusions. Their 18S and 5.8S rDNA sequences were essentially identical, but variations in the ITS1 (62.4 % similarity across 757-bp length), ITS2 (66.9 % similarity across 599-bp length), and 28S (99.0 % similarity across 2,245-bp length) rDNA regions existed between the two isolates. On phylogenetic trees based on the 18S or 28S rDNA sequence, K. neothunni formed a clade with Kudoa spp. with more than four shell valves and polar capsules, particularly K. grammatorcyni and K. scomberomori. Semiquadrate spores of a kudoid species with four shell valves and polar capsules were detected from minute cysts (0.30-0.75 mm by 0.20-0.40 mm) embedded in the trunk muscle of a chub mackerel (Scomber japonicus) fished in the Sea of Japan. Morphologically, it resembled K. caudata described from a chub mackerel fished in the southeastern Pacific Ocean off Peru; however, it lacked filamentous projections on the shell valves of spores. Additionally, it morphologically resembled K. thunni described from a yellowfin tuna also fished in the Pacific Ocean; spores (n = 30) measuring 8.2-10.5 μm in width, 7.0-8.8 μm in thickness, and 6.1-6.8 μm in length; and polar capsule measuring 2.5-3.4 μm by 1.3-2.0 μm. The similarities of the 18S and 28S rDNA sequences between these two species were 98.5 % and 96.3 %, respectively. Simultaneously, the dimensions of cysts in the trunk muscle formed by K. thunni are clearly larger than those of the present species from a chub mackerel: 1.3-2.0 mm by 1.1-1.4 mm (n = 14) vs. 0.30-0.75 mm by 0.20-0.40 mm (n = 7), respectively. Thus, Kudoa scomberi n. sp. is proposed for this multivalvulid species found in the chub mackerel.

Infection dynamics of Kudoa yasunagai (Myxozoa: Multivalvulida) infecting brain of cultured yellowtail Seriola quinqueradiata in Japan

We monitored infection by a brain-infecting myxozoan Kudoa yasunagai in hatchery-reared juvenile yellowtail Seriola quinqueradiata at a culturing site in Japan. Infection was detected by PCR and microscopic observation once every 1 to 4 wk during 2010 and 2011. In both years, we detected first infection in mid-July by PCR. Prevalence increased rapidly after the onset of infection, peaking at 100% within 4 wk. Parasites required less than 10 d to reach the brain after invasion. Development of plasmodia and formation of cysts took 4 to 8 wk. Infection did not reach a plateau and number of cysts tended to decline over time, suggesting possible recovery from the infection. A drastic decline in infection prevalence was observed during the season of highest water temperature (>30°C) in 2010. To understand this phenomenon, we conducted a laboratory experiment to compare infection prevalence and cyst formation in fish kept at 25°C and 30°C. However, we could not detect obvious differences between the treatment groups during the 4 wk of the experiment. There was no apparent pathology associated with the infection. These results suggest that pathological effects of K. yasunagai may differ between fish species or that other factors are important in the development of infectious signs.

Brain infecting kudoids of Australia's coral reefs, including a description of Kudoa lemniscati n. sp. (Myxosporea: Kudoidae) from Lutjanus lemniscatus (Perciformes: Lutjanidae) off Ningaloo Reef, Western Australia

A survey of the myxosporean fauna of Australian marine fishes revealed the presence of a number of putative species of Kudoidae (Multivalvulida) forming pseudocysts between the outer meningeal layer and the outer surface of the brains of the lutjanids Caesio cuning, Lutjanus carponotatus, Lutjanus ehrenbergii and Lutjanus fulviflamma and the mugilid Liza vaigiensis from Lizard Island on the Great Barrier Reef, Australia and Lutjanus lemniscatus off Ningaloo Reef, Western Australia. Morphometric data combined with Bayesian inference and maximum likelihood analyses of small subunit (SSU) and large subunit (LSU) ribosomal DNA (rDNA) was used for species identification and to explore relationships among these taxa. The brain-infecting taxa examined here formed a well-supported clade to the exclusion of non-brain infecting species in the phylogenetic analyses. The combined diagnostic approach identified an undescribed taxon, Kudoa lemniscati n. sp., from the brain of L. lemniscatus (Perciformes: Lutjanidae) off Ningaloo Reef, Western Australia, which we describe and characterise here. K. lemniscati n. sp. can be distinguished from all other species of Kudoa based on the combination of the distinct tropism for forming pseudocysts in the brain tissue, spores with 7 or 8 equal shell valves and 7 or 8 polar capsules, spore size and the differences in the SSU and LSU rDNA sequence data relative to other kudoids. Kudoa chaetodoni was found in the lutjanids C. cuning and L. carponotatus, expanding the known host range for this species to include chaetodontids and lutjanids. L. ehrenbergii and L. fulviflamma were infected with Kudoa lethrini off Lizard Island, a parasite previously known only from lethrinids. Specimens putatively identified as Kudoa yasunagai from Liza vaigiensis and Lutjanus ehrenbergii were morphologically similar and genetically identical over the SSU rDNA dataset to previously reported specimens, but differed by 4 to 11 nucleotides over the LSU dataset from the remaining isolates examined here. While these data are not definitive, they suggest the presence of a K. yasunagai complex.

Morphology and distribution of blood fluke eggs and associated pathology in the gills of cultured Pacific bluefin tuna, Thunnus orientalis

Infestations of blood flukes of the genus Cardicola have been observed in juvenile Pacific bluefin tuna (PBT) cultured in Japan. Infected fish harbor large numbers of parasite eggs in their gills. Although the link between blood fluke infection and juvenile mortality is not clear, accumulation of parasite eggs appears to be pathogenic to the fish. We investigated the origins, general morphology/distribution, and histopathology of these eggs in artificially produced 0 yr old PBT. Dead and live fish were sampled on several occasions from two culture facilities in Wakayama prefecture, Japan. The number of eggs in each gill filament was enumerated under a microscope. In addition, we estimated the total number of eggs by dissolving the gills in a weak NaOH solution. We observed two morphologically distinct egg types in the gill filaments, smaller, oval shaped eggs in the gill lamellae and larger, crescent shaped eggs that occurred primarily in the filamentary arteries. Based on the ITS2 sequence, the ovoid and crescent shaped eggs were identified as C. orientalis and C. opisthorchis, respectively. Eggs of the former species were more abundant (maximum: 6400 per filament) than the latter (maximum: 1400), but the number was highly variable among filaments. The eggs of the latter species were relatively evenly distributed among the filaments. In a heavily infected individual, we estimated a total of >4.5 million eggs were present in the gills on one side of the fish. The number of eggs from the two species was positively correlated to each other and the dead fish tended to harbor more eggs than the live fish. Histological observation revealed host responses around the eggs, including encapsulation by fibroblasts and nodule formation, as seen in response to other aporocotylid eggs. In addition, we observed widespread fusion of gill lamellae and blockage of the filamentary arteries in some instances. Our results provide information that can be used for routine diagnosis of Cardicola blood flukes in cultured tuna and suggest they represent a risk to juvenile PBT.