Kudoa alliaria in flesh of Argentinian hoki Macruronus magellanicus (Gadiformes; Merlucciidae)

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.

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.

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.

Two novel myxosporean parasites in Black Sea fishes: Kudoa niluferi sp. nov. and Kudoa anatolica sp. nov. (Cnidaria: Myxosporea)

Members of the genus Kudoa are typically histozoic and only a few are coelozoic parasites, mainly in marine fishes. In the present study, 2 novel Kudoa species were recovered and described as Kudoa niluferi sp. nov. in the musculature of Neogobius melanostomus and Kudoa anatolica sp. nov. in the musculature, urinary bladder and kidney of Atherina hepsetus collected from the coast of Sinop on the Black Sea. Means ± SD (ranges) of mature spores of K. niluferi sp. nov. were 5.9 ± 0.1 (5.7-6.1) µm in length, 9.2 ± 0.2 (8.8-9.5) µm in width and 7.5 ± 0.3 (7.0-8.1) µm in thickness, while those of K. anatolica sp. nov. were 4.1 ± 0.3 (3.5-4.1) µm in length, 7.1 ± 0.2 (6.7-7.2) µm in width and 5.7 ± 0.2 (5.3-6.0) µm in thickness. In both parasite species, length and width of the 4 polar capsules were not equal and formed 3 distinct size classes, largest (1), intermediate (2) and smallest (1) in size. The prevalence and intensity of infection by K. niluferi sp. nov. were 12.8% and 20-29 parasites (per field-of-view, at 200× magnification), respectively, in the musculature of N. melanostomus. These values for K. anatolica sp. nov. were 32.1% and 10-19 parasites in the musculature as well as 2.9% and 20-29 parasites jointly in the kidney and urinary bladder of A. hepsetus. Phylogenetic analysis based on nuclear small subunit rDNA also suggested K. niluferi and K. anatolica as 2 novel species. These species appeared in the same lineage with K. nova and formed a Black Sea lineage.

Myxozoans as biological tags for stock identification of the Argentine hake, Merluccius hubbsi (Gadiformes: Merlucciidae)

Myxozoans have been successfully used as tags for fish stock identification around the world. However, few studies using myxozoan tags have been carried out in the Southern Atlantic, a region with complex oceanography that constitutes a potentially suitable scenario for testing the utility of myxozoans as indicators. Its usefulness was tested using six samples of Merluccius hubbsi in two different regions of the Argentine Sea. Generalized linear models were performed to assess the effects of fish size and sex, and year and region of capture and selected using the Information Theoretic approach. Three myxozoan species were recorded: Kudoa rosenbuschi, Myxoproteus meridionalis and Fabespora sp. Results of modelling species individually showed differential capabilities for detecting geographical population structure at different spatial scales, with K. rosenbuschi and Fabespora sp. allowing the discrimination of northern and southern stocks, but Fabespora sp. also as a promissory indicator of intrapopulation sub-structure due to different migratory routes during non-reproductive periods. This work confirms that myxozoans offer a set of suitable markers at different spatial scales, which can be selected individually or in any combination, depending on the geographical extent of the study, constituting tools adaptable to the objectives of further research on fish population structure.

Myxobolus neurophilus Guilford 1963 (Myxosporea: Myxobolidae): a common parasite infecting yellow perch Perca flavescens (Mitchell, 1814) in Saskatchewan, Canada

The goal of this study was to identify a myxosporidian parasite infecting the central nervous system of yellow perch Perca flavescens (Mitchell, 1814) observed while investigating a fish kill in Saskatchewan, Canada. Fish were collected from seven different lakes, from two distinct watersheds. Sixty-four per cent (54/86) of yellow perch contained myxozoan pseudocysts located throughout the spinal cord and brain. Myxospores measured 16.5 μm (range 16.2-16.8) long and 8.2 μm (range 7.9-8.4) wide and contained two pyriform, mildly dissymmetrical, polar capsules measuring 7.7 μm (range 7.3-8.1) long and 2.7 μm (range 2.4-3.0) wide. The polar capsules each contained a single polar filament, with 7-9 turns per polar filament coil. Sequencing of the 18S SSU rDNA gene demonstrated >99% similarity to Myxobolus neurophilus. In 60% of infected fish, there was a mild to moderate, non-suppurative myelitis or encephalitis, or both, associated with myxospores. Axonal degeneration was present in rare cases. These findings extend the geographical distribution of M. neurophilus and suggest it may be widespread in yellow perch populations in Saskatchewan.

Thelohanellus testudineus n. sp. (Myxosporea: Bivalvulida) infecting the skin of allogynogenetic gibel carp Carassius auratus gibelio (Bloch) in China

A Thelohanellus species was encountered during a survey on Thelohanellus diversity of Carassius auratus gibelio (Bloch) in China. The infection is characterized by the presence of large cysts of 1.4-3.2 cm in diameter in the skin of host. Mature spores were ampullaceous in frontal view and testudinate in lateral view, measuring 19.7 ± 0.7 (18.6-20.8) μm long, 7.6 ± 0.4 (6.6-8.4) μm wide and 7.3 ± 0.5 (6.6-8.8) μm thick. The single polar capsule was elongated pyriform, with 11.1 ± 0.5 (10.0-11.9) μm long and 5.3 ± 0.3 (4.3-5.8) μm wide. Polar filaments coiled with 7-8 turns. Scanning electron microscopy revealed a smooth spore surface with flat side and convex side. The sutural line was straight or 'S' like, running near the middle of the valves. Histologically, the large cysts consisting of numerous small plasmodia developed in the dermis of the skin. The BLAST search indicated that the newly obtained ssrRNA gene sequences did not match any available sequences in GenBank and phylogenetic analysis placed it in the Thelohanellus clade. Based on morphology and molecular differences with reported Thelohanellus spp., this parasite was described as a new species of genus Thelohanellus.

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.

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.

Remarks on the validity of Myxobolus ampullicapsulatus and Myxobolus honghuensis (Myxozoa: Myxosporea) based on SSU rDNA sequences

In the present study, we isolated three populations of Myxobolus ampullicapsulatus from the gills of crucian carp, Carassius auratus auratus, two from Yongchuan, Chongqing area and one from Poyang Lake, Jiangxi area, China, sequenced their complete small subunit ribosome RNA gene, analyzed their genetic distance and gene similarity, and explored their relationship based on Bayesian inference and maximum likelihood analyses of their small subunit ribosomal DNA. The results combined with their morphological characteristics suggest that M. ampullicapsulatus infecting the gills and pharynx of allogynogenetic gibel carp, Carassius auratus gibelio, should be Myxobolus honghuensis. This study highlights the importance of DNA sequence comparisons for distinguishing Myxobolus species and indicates that the intra-species identification for the two Myxobolus species mentioned in the present research should be less than ten variation sites. In morphology, M. honghuensis Liu et al. (2012) parasitic on the gills of C. auratus auratus (goldfish) was collected from Chongqing area, and its mature spore was 16.5–19.5 × 8.5–10.0 μm in size, polar capsule was 7.0–10.0 × 2.5–4.0 μm in size, and polar filament had 9–10 coils. M. honghuensis Liu et al. (2012) isolated from the pharynx of C. auratus gibelio was sampled in Hubei area, and its mature spore was 15.1–19.5 × 9.0–11.3 μm in size, polar capsule was 7.9–8.1 × 3.0–4.5 μm in size, and polar filament had 7–8 coils.

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.

Supplemental description of Myxobolus squamalis (Myxozoa)

Myxobolus squamalis is a myxozoan skin parasite first reported from rainbow trout (Oncorhynchus mykiss). Identification of the parasite based on myxospore morphology is unreliable because M. squamalis is similar to several other myxobolids that share host species and geographic ranges. The only ssrRNA gene sequence available for M. squamalis is from Chinook salmon, Oncorhynchus tschawytscha, but these data are not linked with any information on spore morphology. Here we provide a supplemental description of M. squamalis from its type host, O. mykiss, using myxospore morphology, morphometry, and ssrRNA gene sequence data. Our ssrRNA sequence data were only 78% similar to the GenBank M. squamalis sequence from Chinook salmon, which raises the possibility of misidentification. We suggest that Chinook salmon are not a host of the parasite, as no infections were found in current stocks or in >30 yr of historical data from hatchery fish held in waters that harbored M. squamalis in rainbow trout, and we could find no well-identified report of M. squamalis from Chinook salmon. Our complementary morphological and molecular data sets will facilitate unambiguous future identification of M. squamalis.

Low host specificity in the Kudoidae (Myxosporea: Multivalvulida) including seventeen new host records for Kudoa thalassomi

Kudoid parasites are known to infect a large variety of fish. A significant proportion of Kudoa species have relatively low host specificity, with a single species able to infect multiple host species representing various host families even from different host orders. Since DNA sequences have been associated with myxosporean species characterisations, it has become far easier to determine host range of new species and validate host records from earlier descriptions. This study investigated the host specificity of a kudoid parasite, Kudoa thalassomi Adlard, Bryant, Whipps et Kent, 2005, from the Great Barrier Reef in Australia using DNA sequence analysis and morphology. The results revealed the host specificity to be broad, with K. thalassomi identified in 18 different fish species representing six different fish families. This study also compares current genetic information from different host isolates of Kudoa Meglitsch, 1947 to their host ranges recorded in existing literature. From this analysis, only half of the Kudoa species with multiple host records (27 Kudoa species) have half or more isolates that are genetically characterised, and thus specifically identified with a high confidence, from their known hosts. Only five kudoid species have genetically characterised isolates from all of their recorded hosts.

Redescription and molecular analysis of Myxobolus shantungensis Hu, 1965 (Myxozoa: Myxosporea) infecting common carp Cyprinus carpio haematopterus

Myxobolus shantungensis Hu, 1965 infects gill arches of common carp Cyprinus carpio haematopterus (Temminck and Schlegel), causing serious pathological effects on host fish. An inadequate original description and absence of molecular data make accurate early diagnosis challenging. To augment the original description, M. shantungensis is redescribed here using morphological and molecular biological methods. Mature spores of M. shantungensis were ellipsoidal or apple shaped in frontal view and lemon shaped in lateral view, averaging 8.2  ±  0.3 μm (8.0-9.0 μm) ×  10.1 ±  0.5 μm (9.2-11.1 μm)  ×  6.9  ±  0.3 μm (6.0-7.4 μm). Some spores had three to four "V"-shaped valve edge markings on the posterior of the spore. The two equal polar capsules were oval, measuring 4.3  ±  0.3 μm (3.8-5.0 μm)  ×  3.2  ±  0.2 μm (2.8-3.5 μm), situated at the anterior extremity of the spore. Polar filaments coiled with six to seven turns. Scanning electron microscopy revealed that the surface of mature spores of M. shantungensis was generally pitted with a number of irregular ridges in shape. M. shantungensis is also characterized on the molecular level using the sequence of the small subunit ribosomal RNA gene. A BLAST search revealed that this sequence did not match any available sequences in GenBank.

Supplemental diagnosis of a myxozoan parasite from common carp Cyprinus carpio: synonymy of Thelohanellus xinyangensis with Thelohanellus kitauei

Thelohanellus kitauei Egusa et Nakajima, 1981, was described from common carp Cyprinus carpio L. in Japan. In China, a myxosporean infecting the intestinal tissue of the same host species was described as Thelohanellus xinyangensis Xie, Gong, Xiao, Guo, Li et Guo, 2000, despite many similarities to T. kitauei. To examine the potential conspecificity of these species, a morphological and molecular investigation of T. xinyangensis was conducted. Comparing myxospore morphology, the mean spore length and width of each species is not identical between species, but ranges of dimensions overlap. These data are more suggestive of intraspecific variation than distinct species. Comparison of relative ratios of spore length to polar capsule length and spore width to polar capsule width of T. xinyangensis and T. kitauei reveal no differences and scanning electron microscopy reveals a smooth spore surface of T. xinyangensis, which is consistent with that of T. kitauei. Most convincingly, DNA sequences of the small subunit ribosomal RNA (ssrRNA) gene of the two species were identical. From the morphological and molecular biological data, we propose T. xinyangensis from the intestine of common carp is not a distinct species and is synonymous with T. kitauei.

Kudoa iwatai and two novel Kudoa spp., K. trachuri n. sp. and K. thunni n. sp. (Myxosporea: Multivalvulida), from daily consumed marine fish in western Japan

Infection of marine fish by certain myxosporean species of the genus Kudoa results in unsightly cyst formation in the trunk muscle or post-mortem myoliquefaction, causing a great economic loss to aquaculture industries, capture fisheries, and fish dealers. In addition, consumers encountering unsightly Kudoa cysts in fish fillets believe them to be unknown foreign materials acquired during processing. To identify prevalent Kudoa spp. encountered in daily life by the Japanese population, fresh fish slices (sashimi) or fish fillets with whitish spots were collected during a 7-month period (May to December 2008) at local markets in the city of Yamaguchi, western Japan. Kudoa cysts were found in three Japanese seaperches (Lateolabrax japonicus), two black sea bream (Acanthopagrus schlegelii), two Japanese jack mackerel (Trachurus japonicus), and one albacore (Thunnus alalunga). Kudoa iwatai was identified in all the examined Japanese seaperch and black sea bream from Japan's Inland Sea, as assessed by morphology and genetic analysis of the 18S and 28S ribosomal RNA gene (rDNA). Kudoa trachuri n. sp. from two Japanese jack mackerel fished in the Japanese Sea off Nagasaki and Kudoa thunni n. sp. from one albacore fished in the Pacific Ocean had a spore, which was semiquadrate in shape in apical views and ovoid in lateral views, with four equal shell valves and drop-like polar capsules. Scanning electron microscopy revealed that these three Kudoa species had different types of small projections at the apex of each valve. The 18S and 28S rDNA sequences of K. trachuri n. sp. and K. thunni n. sp. were found to be closely related to those of Kudoa crumena; however, these sequences were distinct in each of the species, which additionally exhibited different morphological features.

Phenotypic variation in a significant spore character in Kudoa (Myxosporea: Multivalvulida) species infecting brain tissue

Some Kudoa species display variations in the number of polar capsules in spores within an individual pseudocyst. Nonetheless, there is usually a dominant morphotype which forms a significant element of diagnosis. In 2007, a Kudoa isolate from whiting (spores with 5 (dominant) or 6 (minor) polar capsules) was characterized by Burger et al. (2007) as being 100% identical in SSU rDNA to Kudoa yasunagai (spores with 7 polar capsules) from a halibut, despite its obvious morphological differences. The authors hypothesized that either SSU rDNA had reached its level of resolution or that the genetic identity revealed conspecificity. To further investigate these hypotheses, SSU and LSU rDNA sequence data were coupled with principal components, correlation, and regression analyses of morphometric data from different kudoid isolates that infect brain tissue to determine the relationships between spore morphotypes and different kudoid isolates. The trends in morphometrics between the spores of particular isolates were so similar that it was concluded that the molecular results did indicate conspecificity rather than SSU reaching its level of resolution. This phenotypic influence on a significant diagnostic character within the Kudoidae has a major impact on the diagnosis of this, and potentially other, pathogenic species.

Four new species of KudoaMeglitsch, 1947 (Myxosporea: Multivalvulida) from Australia with recommendations for species descriptions in the Kudoidae

Kudoid parasites are significant pathogens of marine fish. In the past, specific identification has been difficult due to a paucity of detailed morphological and biological information provided in the original description of some species. However, the introduction of DNA analysis has dramatically improved diagnosis. For morphological characterization, this paper proposes a new set of schematics including additional measurements to give a more thorough description of spore morphology, and provides evidence for uniqueness of 4 new species: Kudoa gunterae n. sp. (from 10 pomacentrid species and 1 apogonid species), K. kenti n. sp. (from 4 pomacentrid species), K. paraquadricornis n. sp. (from 4 carangid species), and K. whippsi n. sp. (from 8 pomacentrid species and 1 apogonid species). Subtle morphological differences found between closely related species were reflected in their genetics, with increased resolution provided by the large subunit, compared with that of the small subunit, of the ribosomal DNA gene region. This article proposes comprehensive requirements for species descriptions within the Kudoidae that incorporate biology, morphology, and genetic sequence.

Myxosporean infection in frozen blocks of Patagonian hakes

Numerous pseudocysts of the myxosporean genus Kudoa were found infecting the body musculature of commercial frozen blocks of Patagonian hakes of the species Macruronus magellanicus, Merluccius australis, and Merluccius hubbsi. Pseudocysts consisted of numerous diminutive quadrate spores with four polar capsules. The small subunit ribosomal DNA was amplified, cloned, and sequenced for phylogenetic study. Minimum evolution and maximum parsimony analyses placed the resulting sequences in a clade with Kudoa species of Patagonian hakes, K. rosenbuschi and K. alliaria, with bootstrap values of 99%. Molecular and morphological results indicated that the above species were the same, with some differences based on host-related factors. Minor muscular damage appeared as a focal distortion of host fiber architecture to accommodate the parasite. The mild host response consisted of different stages of encapsulation. In cases of concurrent heavy infections, these fish are unappealing as food, due to the parasite's potential effect on the market's perception of macroscopic, unsightly cysts in fish musculature.

A new species of Henneguya (Myxozoa) in the big-eyed scad (Selar crumenophthalmus) from Hawaii

We describe a new myxozoan, Henneguya akule n. sp., infecting the carangid fish Selar crumenophthalmus in Hawaii. Spores were found only in the aortic bulb, characterized by elliptical capsule with 2 tails, and pyriform polar capsules that angled toward the anterior end of the spore. Polar filaments had 3-4 coils. Parasites were present in apparently healthy fishes and caused no evident gross pathology. On microscopy, parasites evinced a mild inflammatory response in the host characterized by accumulations of eosinophilic fibrillar material around spores and a mononuclear infiltrate in the adventitia of the bulbus arteriosus. Overall prevalence was 20%, and prevalence between 2001 and 2006 ranged from 12 to 27%, but did not differ significantly between years. In contrast, prevalence of infection was highest in south-central Oahu. There was no relationship between infection status and body condition or gender of fish, and infection was absent in the smallest and largest fishes. Phylogenetically, H. akule n. sp. is most closely related to other Henneguya species infecting the heart of marine fishes based on ribosomal DNA analysis. This is the first documentation of a myxozoan parasite in marine fishes from Hawaii.

Patterns of relatedness in the Kudoidae with descriptions of Kudoa chaetodoni n. sp. and K. lethrini n. sp. (Myxosporea: Multivalvulida)

Two morphologically novel Kudoa species are characterized from brain tissue of fish, Kudoa chaetodoni n. sp. from Chaetodon unimaculatus (Chaetodontidae) and Kudoa lethrini n. sp. from Gymnocranius audleyi and Lethrinus harak (Lethrinidae). Additionally we characterized a 5-spore valve (SV) Kudoa species from the brain of Sillago ciliata (Sillaginidae). Intriguingly, its 18S rDNA sequence was identical to that of the 7 SV Kudoa yasunagai extracted from the brain of a paralichthyid halibut in Japan. These 2 species may either prove to be con-specific, even though morphology and distribution differ, or demonstrate the limit of specific resolution in the small subunit rDNA gene region. Small subunit rDNA sequences from these new species were used in molecular phylogenetic analyses of kudoids to examine congruence of phylogeny with tissue tropism, geographical distribution, and host specificity. There was significant correlation between tissue tropism in the form of well-supported brain and heart-infecting clades. Host specificity and geographical distribution showed some correlations with genotype.

Phylogeography of the cosmopolitan marine parasite Kudoa thyrsites (Myxozoa: Myxosporea)

Kudoa thyrsites (Myxozoa: Multivalvulida) is a cosmopolitan marine parasite of fishes associated with post-mortem tissue degradation. Financial losses incurred as a result of these infections are of concern to commercial fisheries. There is conflicting evidence whether K. thyrsites represents a cryptic species complex. Myxospore morphology is very similar for K. thyrsites across its range, but preliminary genetic analyses show some differences. Kudoa thyrsites and the morphologically similar Kudoa histolytica were examined from hosts in British Columbia, Canada, Oregon, USA, Chile, England, South Africa, Australia, and Japan. We compared myxospore morphology and DNA sequences of heat shock protein 70 and the small subunit, large subunit, and internal transcribed spacer 1 of the ribosomal DNA. There was some morphological variation between regional representatives, inconsistent with genetic analyses. Phylogenetically, major separations correlated to four broad geographic regions: Japan, Australia, eastern Pacific, and eastern Atlantic. Within these regions there was little additional genetic structure. These data are evidence for regional subdivision of K. thyrsites suggesting global transplantation of fishes has yet to homogenize these distinctions. Within regions, parasite gene flow appears to be high between host species, suggesting little host specificity and minimal cryptic speciation. Our data also indicate that K. histolytica is not a valid species, as it was morphologically and genetically indistinguishable from K. thyrsites.