Description of Discocotyle ciray n. sp. (Monogenea: Discocotylidae) from Parahucho perryi (Brevoort) from Hokkaido, Japan, with a redescription of D. sagittata (Leuckart, 1842)

Discocotyle sagittata (Leuckart, 1842) (Monogenea: Discocotylidae) is redescribed, based on specimens collected from the type host, Salmo trutta Linnaeus, from the type locality, Freiburg, Germany, supplemented with specimens from S. trutta and rainbow trout, Oncorhynchus mykiss (Walbaum) reared in an Austrian aquarium. The diagnosis of the genus Discocotyle Diesing, 1850 is emended. Discocotyle ciray n. sp. is described, based on immature, preadult and adult specimens from the salmonid, Parahucho perryi (Brevoort) at Eniwa, Hokkaido, Japan. Adult specimens of the new species were about twice as large as those of D. sagittata from S. trutta. When the type specimens of D. ciray n. sp. were examined together with museum specimens from P. perryi at Tsurui, Hokkaido, the body and clamp sizes were positively correlated to the host size. Their measurements from a smaller P. perryi at Tsurui overlapped with those of D. sagittata, showing that these size differences were not suitable differentiating keys. Discocotyle ciray n. sp. can be separated from D. sagittata by the morphologies of the female genital system (relatively anteriorly positioned ovary, short joint vaginal duct and much more strongly winding uterus). The genetic distances of COI mtDNA sequence between D. ciray n. sp. and D. sagittata were 18.0-18.6%. These remarkable genetic divergences also supported the distinct taxonomic status of D. ciray n. sp.

Comparison of skin mucus lectins among longtooth grouper Epinephelus bruneus and giant grouper E. lanceolatus as well as the hybrid, Kue-Tama, and their binding abilities to the skin fluke Benedeniaepinepheli

Interspecific hybrids of farm-raised fish are becoming popular in aquaculture owing to their advantages over pure species, including improved growth and higher resistance to infectious diseases. Kue-Tama is a recently established hybrid grouper derived from the longtooth grouper Epinephelus bruneus (♀) × giant grouper E. lanceolatus (♂). In our previous study, this hybrid showed significantly higher resistance against the skin fluke Benedenia epinepheli, a problematic parasite in grouper farming, than the longtooth grouper. In the present study, we explored lectins in the skin mucus of hybrids and their parent species. While C-type lectins of approximately 15 kDa were obtained from longtooth groupers, additional C-type lectins with molecular masses of approximately 20 and 30 kDa, as well as 45-kDa F-type lectin, were also detected in Kue-Tama and giant groupers. Semi-quantitative reverse transcript-polymerase chain reaction (RT-PCR) demonstrated that the gene expression levels of both C-type and F-type lectins were significantly higher in the skin of the hybrid and giant groupers than that of the longtooth grouper. In addition, some skin mucus lectins of the hybrid and giant groupers were bound to the fluke, suggesting that these lectins conferred resistance to parasitic infections.

Synopsis of myxosporean species (Cnidaria: Myxozoa) parasitizing fishes from Vietnam

This paper provides an updated checklist of species-level identified myxosporeans from marine and freshwater fishes in Vietnam. The list includes 51 nominal species (38 marine and 13 freshwater) belonging to 9 genera: Myxobolus Bütschli, 1882 (26 species); Kudoa Meglitsch, 1947 (6 species); Henneguya Thélohan, 1892 (6 species); Thelohanellus Kudo, 1933 (5 species); Unicapsula Davis, 1924 (2 species); Ceratomyxa Thélohan, 1892 (2 species), Zschokkella Auerbach, 1909 (2 species); Auerbachia Meglitsch, 1960 (1 species), and Meglitschia Kovaleva, 1988 (1 species). For each parasite species, information on myxospore morphology, line drawings, fish hosts, infection sites, and collection locality in Vietnam are reported. Where available, we also provide GenBank accession numbers for nucleotide sequence data. In addition, taxonomic status of several species was discussed and Myxobolus eszterbaueri nom. nov. is proposed as a junior homonym for Myxobolus hakyi Baska, Voronin, Eszterbauer, Müller, Marton & Molnár 2009, which is preoccupied.

Molecular and morphological description of a novel microsporidian Inodosporus fujiokai n. sp. infecting both salmonid fish and freshwater prawns

A new microsporidian disease of cultured rainbow trout Oncorhynchus mykiss has recently been confirmed in Japan, and the causative species was tentatively designated as Microsporidium sp. RBT-2021. Involvement of common prawn Palaemon paucidens in its transmission was suggested based on the previous feeding trials, although the microsporidian infection in P. paucidens was not confirmed. In this study, P. paucidens in Lake Biwa, Japan was investigated for microsporidian infection and 4 types of spores (types 1-4) were newly found. The nucleotide sequence of the small subunit ribosomal RNA gene was identical between type 1 and Microsporidium sp. RBT-2021, indicating they are conspecific. However, intriguingly, the spore morphology and the mode of development in fish and prawn were strikingly different. Morphological observations revealed type 1 in the prawn possesses characteristics of the genus Inodosporus Overstreet and Weidner, 1974, while Microsporidium sp. RBT-2021 in the trout exhibited the characteristics of the genus Kabatana Lom, Dyková and Tonguthai, 2000. In the phylogeny, type 1 was placed within a clade comprising Kabatana spp. and Inodosporus octosporus. Based on the morphological and molecular analyses, we describe Microsporidium sp. RBT-2021 as Inodosporus fujiokai n. sp. Together with the success of the previous prawn-feeding trials, this study strongly suggests I. fujiokai n. sp. has a multi-host life cycle utilizing fish and crustacean hosts and different modes of development in each host. Such polymorphic life cycle has barely been known among fish microsporidians. This study also suggests that the genus Kabatana is a junior synonym of the genus Inodosporus.

Description of Myxobolus hoabinhensis n. sp. (Myxosporea: Myxobolidae), infecting the trunk muscles of goldfish Carassius auratus (Linnaeus, 1758) (Cypriniformes: Cyprinidae) in northern Vietnam

During a survey of myxosporean parasites of freshwater fishes in northern Vietnam, myxospores resembling those of the genus Myxobolus (Myxosporea: Myxobolidae) were found in the trunk muscle of 6 out of 35 specimens (17.14%) of wild goldfish Carassius auratus (Cypriniformes: Cyprinidae). The mature spores were 12.0 ± 0.4 (11.4 - 12.6) µm long, 8.5 ± 0.2 (7.9 - 9.0) µm wide and 6.1 ± 0.2 (5.8 - 6.3) µm thick, containing two pyriform-shaped polar capsules unequal in size. The larger polar capsule was 7.6 ± 0.3 (7.1 - 8.4) µm long and 3.5 ± 0.1 (3.3 - 3.8) µm wide, and the smaller polar capsule was 6.2 ± 0.3 (5.5 - 6.7) µm long and 2.9 ± 0.2 (2.6 - 3.4) µm wide. Each polar capsule contained a polar filament with 3-5 coils. A phylogenetic analysis based on the small subunit rDNA (SSU rDNA) sequence revealed that this Myxobolus species forms a distinct branch in the phylogenetic tree sister to Myxobolus artus and Myxobolus cyprini, with DNA sequence similarity at 97.6% to M. artus and 97.5% to M. cyprini. A combination of the morphological characteristics and molecular data suggest that this is an undescribed species, and we propose the name Myxobolus hoabinhensis n. sp.

Praziquantel use in aquaculture - Current status and emerging issues

Parasitic diseases are major constraints in fish mariculture. The anthelmintic praziquantel (PZQ) can effectively treat a range of flatworm parasites in a variety of fish species and has potential for broader application than its current use in the global aquaculture industry. In this review we report on PZQ's current use in the aquaculture industry and discuss its efficacy against various flatworm parasites of fish. Routes of PZQ administration are evaluated, along with issues related to palatability, pharmacokinetics and toxicity in fish, while PZQ's effects on non-target species, environmental impacts, and the development of drug-resistance are discussed.

A world of taxonomic pain: cryptic species, inexplicable host-specificity, and host-induced morphological variation among species of Bivesicula Yamaguti, 1934 (Trematoda: Bivesiculidae) from Indo-Pacific Holocentridae, Muraenidae and Serranidae

The taxonomy of species of Bivesicula Yamaguti, 1934 is analysed for samples from holocentrid, muraenid and serranid fishes from Japan, Ningaloo Reef (Western Australia), the Great Barrier Reef (Queensland), New Caledonia and French Polynesia. Analysis of three genetic markers (cox1 mtDNA, ITS2 and 28S rDNA) identifies three strongly supported clades of species and suggests that Bivesicula as presently recognized is not monophyletic. On the basis of combined morphological, molecular and biological data, 10 species are distinguished of which five are proposed as new. Bivesicula Clade 1 comprises seven species of which three are effectively morphologically cryptic relative to each other; all seven infect serranids and four also infect holocentrids. Bivesicula Clade 2 comprises three species of which two are effectively morphologically cryptic relative to each other; all three infect serranids and one also infects a muraenid. Bivesicula Clade 3 comprises two known species from apogonids and a pomacentrid, and forms a clade with species of Paucivitellosus Coil, Reid & Kuntz, 1965 to the exclusion of other Bivesicula species. Taxonomy in this genus is made challenging by the combination of low resolving power of ribosomal markers, the existence of regional cox1 mtDNA populations, exceptional and unpredictable host-specificity and geographical distribution, and significant host-induced morphological variation.

Three new species of Helicometroides Yamaguti, 1934 from Japan and Australia, with new molecular evidence of a widespread species

We report specimens of monorchiids infecting Haemulidae from the waters off Japan and Australia; these specimens represent five species of Helicometroides Yamaguti, 1934, three of which are unambiguously new. Helicometroides murakamii n. sp. infects Diagramma pictum pictum from off Minabe, Japan; Helicometroides gabrieli n. sp. infects Plectorhinchus chrysotaenia from off Lizard Island, Australia; and Helicometroides wardae n. sp. infects Plectorhinchus flavomaculatus and Plectorhinchus multivittatus from off Heron Island, Australia. Helicometroides murakamii n. sp. and H. gabrieli n. sp. conform to the most recent diagnosis of Helicometroides in lacking a terminal organ, but H. wardae n. sp. possesses a terminal organ with distinct, robust spines; despite this morphological distinction, the three form a strongly-supported clade in phylogenetic analyses. We also report specimens morphologically consistent with Helicometroides longicollis Yamaguti, 1934, from D. pictum pictum from off Minabe, Japan, and Diagramma pictum labiosum on the Great Barrier Reef, Australia. Genetic analyses of ITS2 rDNA, 28S rDNA and cox1 mtDNA sequence data for the Japanese specimens reveal the presence of two distinct genotypes. Specimens of the two genotypes were discovered in mixed infections and are morphologically indistinguishable; neither genotype can be associated definitively with H. longicollis as originally described. We thus identify them as H. longicollis lineage 1 and 2, pending study of further fresh material. Genetic analyses of specimens from the Great Barrier Reef are consistent with the presence of only H. longicollis lineage 1. This species thus has a range that incorporates at least Australia and Japan, localities separated by over 7000 km.

Morphological and molecular characterization of Ceratomyxa binhthuanensis n. sp. (Myxosporea: Ceratomyxidae) from the gall bladder of blacktip grouper Epinephelus fasciatus (Perciformes: Serranidae) in the East Sea of Vietnam

A new myxozoan species, Ceratomyxa binhthuanensis n. sp. (Myxosporea: Ceratomyxidae), was found in the gall bladder of blacktip grouper Epinephelus fasciatus (Perciformes: Serranidae) in the East Sea of Vietnam. Myxospores were observed floating free in the gall bladder of 3 out of 20 fish examined (15%). Mature myxospores were elongate and slightly crescent-shaped and measured 12.2 ± 1.3 (10.8-16.0) μm in thickness and 5.8 ± 0.6 (4.8-6.9) μm in length, with two smooth equal shell valves. The two polar capsules were spherical and equal in size, measuring 2.6 ± 0.3 (2.3-2.9) μm in diameter. The posterior angle was slightly concave, 153.7° ± 5.6° (148.9°-166.0°). Molecular analysis of SSU rDNA sequence showed that Ceratomyxa binhthuanensis n. sp. differs from other Ceratomyxa spp. available in GenBank. Phylogenetic analysis indicated that C. binhthuanensis n. sp. was closely related to three species, Ceratomyxa nolani, Ceratomyxa yokoyamai, and Ceratomyxa cutmorei, which also infect fish hosts of the genus Epinephelus.

Two new species of threadlike blood flukes (Aporocotylidae), with a molecular revision of the genera Ankistromeces Nolan & Cribb, 2004 and Phthinomita Nolan & Cribb, 2006

Ankistromeces Nolan & Cribb, 2004 and Phthinomita Nolan & Cribb, 2006 are sister genera of threadlike blood flukes (Trematoda: Aporocotylidae) infecting teleost fishes of the tropical Indo-west Pacific. Here, we report new collections of these genera from Australia, Indonesia, and Japan. A new species of Ankistromeces, Ankistromeces kawamurai n. sp., is described from Siganus spinus (Linnaeus) off Okinawa, Japan, and a new species of Phthinomita, Phthinomita abdita n. sp., from Choerodon cephalotes (Castelnau), in Moreton Bay, Australia; the new species are morphologically cryptic within their respective genera and are delineated by molecular and ecological data. Ankistromeces olsoni Nolan & Cribb, 2006 is reported from Siganus fuscescens (Houttuyn) off Heron Island (southern Great Barrier Reef), Lizard Island (northern Great Barrier Reef), and Okinawa and Wakayama Prefectures, Japan and from Siganus spinus (Linnaeus) from off Bali, Indonesia. Ankistromeces mariae Nolan & Cribb, 2004 is re-reported from the type-host, Meuschenia freycineti (Quoy & Gaimard), from a new location, Gypsy Bay, Tasmania. Phthinomita poulini Nolan & Cribb, 2006 is re-reported from its type-locality, Lizard Island, from a range of mullids, including five new host species, and its range is extended to include Moreton Bay. Phthinomita symplocos Nolan & Cribb, 2006 is reported from Bali and P. hallae Nolan & Cribb, 2006, P. jonesi Nolan & Cribb, 2006, P. littlewoodi Nolan & Cribb, 2006, and P. munozae Nolan & Cribb, 2006 are each re-reported from their type-host and type-localities. New cox1 mtDNA data were generated for all known species of these two genera from new and archival material. Analyses of these data enabled an evaluation of all known Phthinomita species; P. robertsthomsoni Nolan & Cribb, 2006 is synonymised with P. adlardi Nolan & Cribb, 2006, and P. brooksi Nolan & Cribb, 2006 is synonymised with P. sasali Nolan & Cribb, 2006. We highlight the failure of ITS2 data to delineate closely related aporocotylid species. In contrast, cox1 sequence data are proving reliable and effective in this context and we recommend their incorporation in future studies of blood fluke taxonomy.

Phototactic responses in four monogenean oncomiracidia

Phototaxis is the common behavioral response exhibited by the oncomiracidia of various monogeneans. However, the changes in the oncomiracidial swimming behavior in response to light cues are not well understood. Here, we investigated the light responses of four monogeneans that are important pathogens in mariculture, namely Benedenia epinepheli, Benedenia seriolae, Neobenedenia girellae, and Heteraxine heterocerca. The swimming trajectory and speed of oncomiracidia of each species were assessed in a glass Petri dish with an LED light placed adjacent to it, based on three different light responses: LED light in the off position (normal swimming), LED light in the on position (phototactic behavior), and immediately (< 5 s) after switching the LED light off (photophobic behavior). The oncomiracidia of all four species exhibited positive phototactic and photophobic responses; however, the change in swimming speed between each response differed among the species. The oncomiracidia of three species (B. epinepheli, N. girellae, and H. heterocerca) exhibited high swimming speed, as a phototactic response; in contrast, the oncomiracidia of B. seriolae exhibited reduced swimming speed when moving toward the light source. Benedenia epinepheli and H. heterocerca exhibited the highest swimming speed during the phototaxis phase, whereas B. seriolae and N. girellae exhibited the highest swimming speed during the photophobic phase. These light responses are considered adaptive traits to increase the chance of encountering and infecting suitable hosts in nature, and such responses could potentially be applied to the control of parasite infections in aquaculture.

A new myxosporean species, Henneguya lata n. sp. (Myxozoa: Myxobolidae), from the gills of yellowfin seabream Acanthopagrus latus (Perciformes: Sparidae) in the Gulf of Tonkin, Vietnam

During a survey of myxosporean parasites of marine fish in the coastal region of Vietnam, a species of the genus Henneguya (Myxosporea: Bivalvulida) was found in the gill of yellowfin seabream Acanthopagrus latus (Perciformes: Sparidae). White and oval cysts, measuring 145-220 μm in diameter, were detected in the gill lamellae of 4 of 15 fish examined (26.7%). Mature myxospores were elongate, with smooth valves, two similar polar capsules, and having the following dimensions: spore body length 9.9 ± 0.5 (8.9-12.5) μm, body width 6.7 ± 0.3 (6.1-7.6) μm, thickness 5.1 ± 0.2 (4.8-5.4) μm, caudal appendage length 10.0 ± 1 (8.3-11.6) μm, and total myxospore length 19.3 ± 1.4 (16.5-21.5) μm. The polar capsules were ovoid, measuring 3.2 ± 0.2 (2.8-3.9) μm long and 1.9 ± 0.2 (1.5-2.3) μm wide. Each polar capsule has a polar filament with 4-5 coils. Histological analysis revealed plasmodia in the connective tissues of the gill lamellae, but inflammation and deformation of the gills were not observed. In the phylogenetic tree reconstructed from the small subunit ribosomal DNA (SSU rDNA), sequences of the Henneguya specimens found in this study form a distinct branch. Morphological characteristics and molecular data identified a new species, namely Henneguya lata n. sp.

In vivo cultivation of tuna blood fluke Cardicola orientalis in terebellid intermediate hosts

Some fish blood flukes of the genus Cardicola (Aporocotylidae) are considered important pathogens of farmed/ranched tuna, Thunnus spp. Infections with Cardicola spp. might obstruct the blood flow in the gills via massive accumulations of eggs and often lead to mass mortalities in captive tuna. At present, oral administration of an anthelminthic drug, praziquantel is the most effective treatment, but the tuna farming industries are seeking non-drug control measures. Development of prophylactic and holistic measures have been difficult, owing to a lack of basic knowledge about these parasites. Unlike other trematodes which use molluscs, blood flukes of marine actinopterygian fish use terebellid polychaetes as intermediate hosts. However, information about the development of Cardicola spp. within intermediate hosts is very limited. Recent success in Cardicola opisthorchis sporocyst transplantation into the host polychaete has opened possibilities for the cultivation of Cardicola in the laboratory. Here, we conducted several transplantation trials with another tuna blood fluke, Cardicol orientalis, into its natural and surrogate polychaete hosts. Cardicola orientalis sporocysts were injected into a total of 195 Nicolea gracilibranchis, the natural host, and clear sporocyst development and reproduction was observed in 32 recipients (overall success rate 16.4%). The production of daughter sporocysts in the transplanted polychaete occurred within 14 days post injection, and one sporocystogenous cycle took approximately 4 weeks. Serial passage culture via transplantation of in vivo-cultured sporocysts was also achieved, but with limited sporocyst reproduction. In addition, sporocysts were successfully retrieved from six and one individuals of the surrogate hosts, Thelepus setosus (n = 10) and Thelepus japonicus (n = 5), respectively. These results indicate that the in vivo cultivation of C. orientalis sporocysts is possible, not only in its natural host but also in other terebellids, although the problems of high mortality and inconsistency in successful transplantation need to be resolved.

Production of a novel monoclonal antibody applicable for an immunochromatographic assay for Kudoa septempunctata spores contaminating the raw olive flounder (Paralichthys olivaceus)

Kudoa septempunctata, a myxosporean parasite of the olive flounder (Paralichthys olivaceus), causes foodborne gastroenteritis after ingestion of contaminated raw flounder. Available methods to detect K. septempunctata require expensive equipment, well-trained personnel, and lengthy procedures. Here we generated a novel monoclonal antibody (MAb 15G11) against K. septempunctata and used it to produce a prototype immunochromatographic assay (prototype Kudoa-ICA). Within 15min, the prototype Kudoa-ICA detected ≥1.0×10⁵spores/mL in a spore suspension and ≥2.0×10⁴spores/g of P. olivaceus muscle. The prototype Kudoa-ICA weakly cross-reacted with spores of K. lateolabracis and K. iwatai. cDNA sequence, expression, and western blot analyses revealed that MAb 15G11 detected an approximately 24-kDa protein encoded by a 573bp mRNA. The cDNA nucleotide and predicted amino acid sequences were not significantly similar to any sequence in the GeneBank database. Immunoelectron microscopy revealed that MAb 15G11 reacted with the sporoplasmic cells and mainly with the capsulogenic cells of the K. septempunctata spore. Although the Kudoa-ICA was weakly cross-reactive with two other Kudoa species, it detected >1.0×10⁶spores/g of K. septempunctata in P. olivaceus muscle, which is the criterion used to indicate a violation of the Food Hygiene Law of Japan. We conclude that MAb 15G11 may be suitable for use in an immunochromatographic assay for screening P. olivaceus muscle contaminated with K. septempunctata at food distribution sites such as food wholesalers, grocery stores, and restaurants.

Developmental stages of fish blood flukes, Cardicola forsteri and Cardicola opisthorchis (Trematoda: Aporocotylidae), in their polychaete intermediate hosts collected at Pacific bluefin tuna culture sites in Japan

Farming of Pacific bluefin tuna (PBT), Thunnus orientalis, is a rapidly growing industry in Japan. Aporocotylid blood flukes of the genus Cardicola comprising C. orientalis, C. opisthorchis and C. forsteri are parasites of economic importance for PBT farming. Recently, terebellid polychaetes have been identified as the intermediate hosts for all these parasites. We collected infected polychaetes, Terebella sp., the intermediate host of C. opisthorchis, from ropes and floats attached to tuna cages in Tsushima, Nagasaki Prefecture, Japan. Also, Neoamphitrite vigintipes (formerly as Amphitrite sp. sensu Shirakashi et al., 2016), the intermediate host of C. forsteri, were collected from culture cages in Kushimoto, Wakayama Prefecture, Japan. The terebellid intermediate hosts harbored the sporocysts and cercariae in their body cavity. Developmental stages of these blood flukes were molecularly identified using species specific PCR primers. In this paper, we describe the cercaria and sporocyst stages of C. opisthorchis and C. forsteri and compare their morphological characteristics among three Cardicola blood flukes infecting PBT. We also discuss phylogenetic relations of the six genera of the terebellid intermediate hosts (Artacama, Lanassa, Longicarpus, Terebella, Nicolea and Neoamphitrite) of blood flukes infecting marine fishes, based on their morphological characters.

Immune reactivity in early life stages of sea-cage cultured Pacific bluefin tuna naturally infected with blood flukes from genus Cardicola (Trematoda: Aporocotylidae)

Pacific bluefin tuna (PBT), Thunnus orientalis, due to its high average price on the market is an economically valuable fish species. Infections by blood flukes from the genus Cardicola (Trematoda: Aporocotylidae) represent a growing concern for the cage culture of bluefin tuna in Japan, Australia and Southern Europe. The accumulation of numerous Cardicola eggs in the fish gills causes severe pathology that has been linked to mortality in PBT juveniles up to one year old. The only effective treatment used to mitigate the infection is the oral administration of the antihelminthic drug praziquantel (PZQ) to the affected fish. However, with the need to minimise therapeutic drug use in aquaculture it is hoped that immunoprophylaxis can provide a future alternative to protect the PBT juveniles against Cardicola infection. Currently, little is known of the host immune response to these parasites and of their infection dynamics. In this study, using real-time qPCR we aimed to quantitatively detect C. orientalis and C. opisthorchis DNA within the gills and heart of cultured PBT juveniles and to investigate the host immune response at the transcriptional level in the gills. The research focused mainly during early stages of infection soon after young PBT were transferred to culture cages (from 14 to 77 days post-transfer). An increase (up to 11-fold) of immune-related genes, namely IgM, MHC-I, TCR-β and IL-1β was observed in the PBT gills infected with Cardicola spp. (28-77 days post-transfer). Furthermore, IgM (19-fold increase) and MHC-I (11.5-fold increase) transcription was strongly up-regulated in gill samples of PBT infected with C. orientalis relative to uninfected fish but not in fish infected with C. opisthorchis. Cardicola-specific DNA was first detected in the host 14 days post-transfer (DPT) to sea-cages which was 55 days earlier than the first detection of parasite eggs and adults by microscopy. Oral administration of PZQ did not have an immediate effect on parasite DNA presence in the host and the DNA presence started to reduce after 24 days only in the host heart. The results provide evidence of an immune response in early age sea-cage cultured juveniles of PBT naturally infected with C. orientalis and C. opisthorchis. This response, whilst not protective against primary infection, provides evidence that immunisation at an early age may have potential as a health strategy.

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.

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.

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.

Transcriptional immune response of cage-cultured Pacific bluefin tuna during infection by two Cardicola blood fluke species

Infections by two blood fluke species, Cardicola orientalis and Cardicola opisthorchis, currently present the greatest disease concern for the sea-cage culture of Pacific bluefin tuna (PBT) - a species of high global economic importance and ecological concern. In this study, we aimed to rapidly, quantitatively, and differentially identify infections by these two parasite species in cultured PBT as well as identify potential host immune responses. Using real-time qPCR, we were successful in quantitatively detecting parasite-specific DNA from within host blood, gill, and heart tissues; positively identifying parasitic infections 44 days earlier than microscopy methods previously employed. Both gill and heart became heavily infected by both parasite species in PBT within two months of sea-cage culture, which was only mitigated by the administration of anthelmintic praziquantel. Nevertheless, fish were observed to mount an organ specific transcriptive immune response during infection that mirrored the relative quantity of pathogenic load. In heart, significant (3-6 fold) increases in IgM, MHC2, TCRβ, and IL-8 transcription was observed in infected fish relative to uninfected controls; whereas in the gills only IgM transcription was observed to be induced (11 fold) by infection. Interestingly, the relative quantity of IgM transcription was highly correlated to the relative abundance of C. orientalis but not C. opisthorchis DNA in the gill samples, even though this organ showed high prevalence of DNA from both parasite species. Taken together, these findings indicate that although ineffective at combating infection during primary exposure, a cellular immune response is mounted in PBT as a potential rejoinder to future Cardicola exposure, particularly against C. orientalis. Although future investigation into antibody effectiveness will be needed, this work provides valuable preliminary insight into host responsiveness to Cardicola infection as well as additional support for the need of anthelmintic treatment following primary parasite exposure during PBT culture.

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.

Henneguya cartilaginis n. sp. (Myxozoa: Myxosporea) in the head cartilage of masu salmon Oncorhynchus masou masou

Henneguya cartilaginis n. sp. (Myxozoa: Myxosporea) is described from wild masu salmon Oncorhynchus masou masou in Hokkaido, Japan. H. cartilaginis n. sp. produced white cysts, up to 3mm in size, in the head of masu salmon. Infected fish exhibited cranial protrusion due to the cysts. Spores (11.4 × 8.6 μm) of H. cartilaginis n. sp. were egg-shaped with the posterior end more pointed and possessed two caudal appendages (34.2 μm average length). Histological observations revealed that large plasmodia possessing fine fibrous pseudopodia on the surface developed in the head cartilage. H. cartilaginis n. sp. resembles H. cerebralis, which was described from the cranial cartilage of Kosogol grayling Thymallus nigrescens in Mongolia. However, they were distinguishable by spore morphology. Molecular analysis of the 18S rDNA sequences indicated that H. cartilaginis n. sp. was most closely related to Henneguya zschokkei, H. nuesslini and H. salminicola of salmonid fish, with genetic similarities of 95.3%, 95.1% and 93.9%, respectively. Based on these differences in spore morphology, molecular data, the site of infection and geographical distribution, the present species is considered to be a new species.

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.

Effect of cadmium on the susceptibility of Tubifex tubifex to Myxobolus cerebralis (Myxozoa), the causative agent of whirling disease

Environmental pollutants alter a wide range of host-parasite interactions in various ways. In some cases, pollution leads to a significant increase in parasite abundance, causing epidemics of parasitic diseases. In other cases, toxicants restrict the transmission success of parasites, resulting in reduction of their abundance. However, very little is known regarding whether and to what extent aquatic pollution affects myxozoan obligate parasites commonly found in fish. We investigated the effect of cadmium (Cd) on the aquatic oligochaete Tubifex tubifex infected with the myxozoan Myxobolus cerebralis. The oligochaetes were experimentally exposed to M. cerebralis myxospores and kept in various concentrations of Cd for 4 mo. Neither survival nor reproduction of the worms was affected by the metal, but infection prevalence and numbers of triactinosmyxon spores produced by individual worms were higher in the Cd-exposed group than the unexposed control. A comparative assay of a lethal Cd concentration (LC50) on infected and non-infected T. tubifex revealed that infected worms are more resistant to the acute toxicity of Cd, probably because uptake of Cd was reduced by the infection. These results suggest that the abundance of M. cerebralis likely increases in polluted waters and escalates the risk of whirling disease in the respective area.

Gymnophallid digenean Parvatrema duboisi uses Manila clam as the first and second intermediate host

To identify the metacercariae of a gymnophallid trematode in the Manila clam Ruditapes philippinarum from the Ariake Sea, experimental infection and molecular analysis were conducted. Based on the morphology of adult worms obtained from experimentally infected mice, the parasite was identified as Parvatrema duboisi. Comparison of internal transcribed spacer (ITS) region of ribosomal DNA (rDNA) sequences for metacercariae and sporocysts from Manila clams and adult worms collected from wild wigeon Anas penelope showed minor differences ranging from 0 to 0.8%. These data strongly suggest that in the Ariake Sea, the parasite has a lifecycle using the Manila clam as the first and second intermediate hosts and wigeon as the definitive host.

Infection dynamics of Neoheterobothrium hirame (Monogenea) on juvenile olive flounder, Paralichthys olivaceus (Temminck & Schlegel), in coastal waters of Japan

A recent epidemic of the invasive monogenean Neoheterobothrium hirame is suspected to have caused the significant decline of the commercial catch of olive flounder, Paralichthys olivaceus, in Japan. To clarify the causal link between parasite invasion and host depletion, we monitored the infections of N. hirame on juvenile flounder for 2 years at two widely separate bays, Obama Bay, experiencing a devastating reduction in flounder catches, and Miyako Bay with a stable catch. Prevalence, mean intensity and abundance of developmental stages of N. hirame were compared between the bays and between fish year classes. Fishes captured at Obama Bay harboured three times more worms than those at Miyako Bay and had a significantly higher overall prevalence of infection. In addition, there was a negative correlation between parasite intensity and host condition factor at Obama Bay, suggesting a causal link between the N. hirame epidemic and the reduction of local flounder populations.

Chronology of parasite-induced alteration of fish behaviour: effects of parasite maturation and host experience

We monitored temporal changes in the magnitude of altered host behaviour in minnows (Pimephales promelas) experimentally infected with metacercariae of a brain-encysting trematode (Ornithodiplostomum ptychocheilus). This parasite develops and then encysts in a region of the brain that mediates the optomotor response (OMR), an innate behaviour that links visual stimuli with motor performance. The OMR of infected and uninfected minnows was evaluated between 0 and 10 weeks post-infection (p.i.), an interval spanning the development period of metacercariae to infectivity in birds. Trials involved monitoring the time an individual minnow spent following a spinning drum that had been painted with alternating black and white stripes. At 2 and 4 weeks p.i., infected minnows followed the drum 40% less often than controls. Differences between controls and infected fish declined thereafter, and were undetectable by 10 weeks p.i. Both control and infected fish habituated equally rapidly to the spinning drum. However, the difference in performance between controls and infected fish was 29% for experienced fish and 48% for fish that had never experienced the drum. Because maximum parasite-induced reduction in OMR coincided with the period of maximum parasite development, the behavioural effects are most likely due to unavoidable pathology in the brain associated with developing larvae.

Intensity-dependent alteration of minnow (Pimephales promelas) behavior by a brain-encysting trematode

We examined the relationship between the numbers of brain-encysting trematodes (Ornithodiplostomum ptychocheilus) and the magnitude of altered behaviors in fathead minnows (Pimephales promelas). Because cysts develop within a brain region that integrates visual stimuli with motor response. we evaluated the standard optomotor response (OMR). Monitoring this task involved recording the time minnows spent following a spinning drum, on which alternating black and white stripes had been painted. Minnows were exposed to 0, 5, 20, 120, and 300 cercariae and then their OMR was evaluated at 2-wk postinfection. Surprisingly, only minnows that had high numbers of parasites (155 +/- 31 worms/fish) or low numbers of parasites (3 +/- 3 worms/ fish) differed significantly in their optomotor performance compared with controls. Reduced OMR of heavily infected minnows was positively correlated with reduction in minnow activity. In contrast, reduced OMR in lightly infected minnows was independent of host activity and was likely associated with the rapid development of parasite larvae within the optic tecta. The nonlinear relationship between parasite intensity and effect on host behavior was consistent with an earlier study, but the underlying mechanisms producing this pattern are unknown.