Marine Fish In Japan Research Articles

Development of single nucleotide polymorphism (SNP) application for detection and genotyping of RSIV-type megalocytiviruses.

Red sea bream iridovirus (RSIV) belonging to the genus Megalocytivirus of the family Iridoviridae is the cause of serious mass mortality of cultured marine fishes. RSIV-type megalocytiviruses show extremely high nucleotide sequence identities. Thus, epidemiological studies on this virus are limited. This study developed two primer sets amplifying the regions possessing single nucleotide polymorphism (SNP) to determine the relationships and divergence of RSIV-type megalocytiviruses isolated from cultured marine fishes in Japan. The two regions were designed according to the genome sequences of the representative RSIV genotype II of megalocytivirus members in GenBank. The SNP 1 and 2 regions have sequences homologous to hypothetical protein ORF 24 and ORF 31, respectively, of RSIV (accession no. AP017456.1). By sequencing the regions, 53 polymorphic sites were identified. The phylogenetic analysis of 25 RSIV-type megalocytivirus isolates, classified into RSIV cluster, was clustered into eight haplotypes (seven haplotypes from Oita, two haplotypes from Ehime, and one haplotype shared between Oita and Ehime). These findings suggested that SNP in the RSIV genome is a powerful application for the detection and identification of RSIV-type megalocytiviruses.

Description of Two New Species of Philometra Costa, 1845 (Nematoda: Philometridae) from Marine Fishes off Japan, with Notes on Philometroides seriolae (Yamaguti, 1935).

Philometrid nematodes (Philometridae) represent a group of more than 200 species parasitic in the body cavity and various body tissues of fishes. Due to morphological and biological peculiarities, the majority of them are known only by their large females. Generally, the fauna of these parasites remains little known. Occasional helminthological examinations of three species of marine fishes in Japan revealed two new and one insufficiently known species of these tissue-dwelling parasites. These were studied with the use of light and scanning electron microscopy. All three nematode species are described. Philometra ostorhinchi sp. nov. (males and females) from the ovary of Ostorhinchus semilineatus (Temminck et Schlegel) (Apogonidae, Perciformes) is characterized mainly by the lengths and structure of spicules and the gubernaculum (spicules 108-120µm long, length of the gubernaculum 78-87µm); it is the only species of philometrids parasitic in a fish belonging to the Apogonidae. The gravid females of Philometra tenuis sp. nov. (only females available) from the head subcutaneous tissues of Conger myriaster (Brevoort) (Congridae, Anguilliformes) differ from congeners mainly in an unusual shape of the anterior oesophageal bulb. Some new data on the morphology of an insufficiently known species Philometroides seriolae (Ishii, 1931), collected from the body musculature of Seriola quinqueradiata Temminck et Schlegel (Carangidae, Perciformes), are provided; the number and arrangement of cephalic papillae in subgravid females of P. seriolae were found to be similar to those in females of the majority of other philometrid species. The present study extends the knowledge of the species composition of philometrids parasitizing marine fishes and of the morphology of P. seriolae, the type species of Philometroides Yamaguti, 1935.

Taxonomic study on crustacean parasites of the flathead grey mullet (Mugil cephalus) and red seabream (Pagrus major) in Hiroshima Bay, Japan

Crustacean fish parasites can be used as bio-indicators of pollution. This study examined the crustacean parasites of flathead grey mullet (Mugil cephalus) and red seabream (Pagrus major) landed at a fishing port in Hiroshima Bay. Specimens were collected from November 2015 to August 2016. Three species of parasitic crustaceans were identified. Caligus sp. (Copepoda: Siphonostomatoida: Caligidae) was collected from the gills of a male flathead grey mullet Mugil cephalus. The genus Caligus is the largest among the parasitic copepods, containing more than 250 species worldwide, and a total of 20 species have been found from marine fishes in Japan. Lernanthropus atrox Heller, 1865 (Copepoda: Siphonostomatoida: Lernaeopodidae) was collected from the gills of a female red seabream Pagrus. Copepods of the genus Lernanthropus are found attached to the gill filaments of marine fishes in the world. This species is known to occur in both Australian and Japanese waters; in Japan, it has been recorded from Tokyo Bay and the Seto Inland Sea. The cymothoid copepod Ceratothoa verrucosa (Schioedte and Meinert, 1883) (Isopoda: Cymothoidae) was found in the buccal cavity of a red seabream Pagrus major. Cymothoid isopods, including Ceratothoa verrucosa, are found in the buccal and gill cavities as well as on the body surface of fish hosts. This species is only known to occur in Japanese waters.

New host records of three Kudoa spp. (K. yasunagai, K. thalassomi, and K. igami) with notable variation in the number of shell valves and polar capsules in spores.

To date, 26 Kudoa spp. (Myxozoa: Myxosporea: Multivalvulida) have been recorded in edible marine fishes in Japan. In the future, it is likely that even more marine fish multivalvulid myxosporeans will be characterized morphologically and genetically, which will aid the precise understanding of their biodiversity and biology. We examined 60 individuals of six fish species collected from the Philippine Sea off Kochi or from the border between the Philippine Sea and East China Sea around Miyako Island, Okinawa, i.e., the southern part of Japan. Newly collected parasite species included Kudoa yasunagai from the brain of Japanese meagre (Argyrosomus japonicus) and Japanese parrotfish (Calotomus japonicus), Kudoa miyakoensis n. sp. and Kudoa thalassomi from the brain and trunk muscle, respectively, of bluespine unicornfish (Naso unicornis), and Kudoa igami from the trunk muscle of Carolines parrotfish (Calotomus carolinus), African coris (Coris gaimard), and Pastel ringwrasse (Hologymnosus doliatus). With the exception of Japanese parrotfish for K. yasunagai, all these fish are new host records for each kudoid species. Notable variation in the number of shell valves (SV) and polar capsules (PC) was observed for all four kudoid species. In particular, spores with seven or eight SV/PC were prominent in K. igami isolates, despite the original Japanese parrotfish-derived description characterizing it as having spores with six, or less commonly five, SV/PC. However, molecular genetic characterization based on the ribosomal RNA gene (rDNA) and mitochondrial DNA (cytochrome c oxidase subunit 1 and ribosomal RNA small and large subunits) found no significant differences in the nucleotide sequences of isolates with different phenotypical features as far as examined in the present study. A newly erected species, K. miyakoensis n. sp., was determined to be phylogenetically closest to brain-parasitizing species, such as K. chaetodoni, K. lemniscati, and K. yasunagai based on rDNA nucleotide sequences, but differed from them morphologically.

Outline and issues of the Red List of threatened marine fishes in Japan

Outline and issues of the Red List of threatened marine fishes in Japan

Construction of a high-coverage bacterial artificial chromosome library and comprehensive genetic linkage map of yellowtail Seriola quinqueradiata

BackgroundJapanese amberjack/yellowtail (Seriola quinqueradiata) is a commonly cultured marine fish in Japan. For cost effective fish production, a breeding program that increases commercially important traits is one of the major solutions. In selective breeding, information of genetic markers is useful and sufficient to identify individuals carrying advantageous traits but if the aim is to determine the genetic basis of the trait, large insert genomic DNA libraries are essential. In this study, toward prospective understanding of genetic basis of several economically important traits, we constructed a high-coverage bacterial artificial chromosome (BAC) library, obtained sequences from the BAC-end, and constructed comprehensive female and male linkage maps of yellowtail using Simple Sequence Repeat (SSR) markers developed from the BAC-end sequences and a yellowtail genomic library.ResultsThe total insert length of the BAC library we constructed here was estimated to be approximately 11 Gb and hence 16-times larger than the yellowtail genome. Sequencing of the BAC-ends showed a low fraction of repetitive sequences comparable to that in Tetraodon and fugu. A total of 837 SSR markers developed here were distributed among 24 linkage groups spanning 1,026.70 and 1,057.83 cM with an average interval of 4.96 and 4.32 cM in female and male map respectively without any segregation distortion. Oxford grids suggested conserved synteny between yellowtail and stickleback.ConclusionsIn addition to characteristics of yellowtail genome such as low repetitive sequences and conserved synteny with stickleback, our genomic and genetic resources constructed and revealed here will be powerful tools for the yellowtail breeding program and also for studies regarding the genetic basis of traits.

Three novel myxobolid species of genera Henneguya and Myxobolus (Myxosporea: Bivalvulida) from marine fish in Japan

Myxosporean genera Henneguya and Myxobolus (Bivalvulida: Myxobolidae) are closely related in morphology and molecular phylogeny, speciose with approximately 1,000 nominal species. The majority of them are recorded from freshwater fish worldwide, and few are known from marine fish. In this study, three myxobolid spp. are described from marine fish around Japan. Two novel Henneguya spp., Henneguya ogawai sp. n. and Henneguya yokoyamai sp. n., are described from two black sea breams (Acanthopagrus schlegelii) fished in the Inland Sea (Setonaikai), Japan. Plasmodia of the former species were localized in the esophageal or intestinal wall, and those of the latter species were in the wall of the gall bladder and peritoneum. Spore development in plasmodia of these two species was synchronous. The spore body of H. ogawai sp. n. was 11.0 (8.9-12.2) μm in length, 6.9 (6.3-7.5) μm in width, 5.9 (5.2-6.6) μm in thickness, with a bifurcated caudal process of equal length, 10.0 (8.4-12.7) μm long; total spore length, 21.1 (19.2-23.4) μm. It contained two polar capsule, 4.3 (3.8-5.2) × 1.9 (1.4-2.3) μm. The spore body of H. yokoyamai sp. n. was 11.0 (10.1-13.7) μm in length, 7.1 (6.6-7.5) μm in width, and 5.6 (4.5-6.4) μm in thickness, with a bifurcated caudal process of equal length, 14.1 (10.8-17.0) μm long; total spore length, 25.0 (21.9-29.2) μm. It contained two polar capsules, 3.7 (3.1-4.2) × 2.0 (1.8-2.4) μm. A novel Myxobolus sp., Myxobolus machidai sp. n., is described from a spotted knifejaw (Oplegnathus punctatus) fished in the Sea of Japan, off Shimonoseki, Yamaguchi Prefecture, Japan. Plasmodia were embedded in the esophageal wall. Its round spore was small in size, 9.0 (8.1-9.4) μm in length, 7.8 (7.5-8.3) μm in width, and 5.5 (5.1-6.0) μm in thickness. It contained two polar capsules, 3.5 (3.2-3.8) × 2.3 (2.2-2.5) μm. Spore development in a plasmodium was asynchronous. Nucleotide sequencing of the small subunit ribosomal RNA gene (SSU rDNA) of these two novel Henneguya spp. revealed a close phylogenetic relationship with the marine clade of Henneguya spp.; however, they were distinct in morphology and SSU rDNA sequence from any known species. M. machidai sp. n. was grouped with freshwater Henneguya spp. in a phylogenetic tree based on the SSU rDNA, distant from a known marine clade of Myxobolus spp. reported mainly from the Mediterranean Sea. This is the first record of Henneguya-Myxobolus spp. from natural marine water in Japan.

Mycobacterium pseudoshottsii Isolated from 24 Farmed Fishes in Western Japan

Mycobacteria isolated from epizootics of farmed fishes in western Japan were examined for the first time using multigenotypic analysis. By analysis of the sequences of the internal transcribed spacer between the 16S and 23S rRNA genes (ITS) region and the partial 16S rRNA, hsp65 and rpoB genes, M. pseudoshottsii was identified as the causative agent in these infections. Prior to this study, only M. marinum has been known as the causative agent of lethal mycobacterial disease in marine fishes in Japan.

Effect of dietary fluoride derived from Antarctic krill (Euphausia superba) meal on growth of yellowtail (Seriola quinqueradiata)

Yellowtail (Seriola quinqueradiata) is the most important cultured marine fish in Japan. Dietary fish meal for yellowtail in aquaculture was replaced with 0.0%, 15.4% and 100.0% Antarctic krill meal (KM0, KM15, and KM100) and with 0.0%, 15.4%, and 100.0% low-fluoride krill meal (LFK0, LFK15 and LFK100). The fish was fed to duplicate fish groups for 92d (KM trial) or 75d (LFK trial), and fish growth was monitored.Dietary fluoride (F−) concentrations (mgkg−1) were 110, 160, and 580 (KM0, KM15, and KM100, respectively) and 98, 120, and 190 (LFK0, LFK15, and LFK100, respectively). The growth during the experimental period, weight gain, feed intake, specific growth rate, and feed efficiency in fish fed the KM100 diet were markedly lower than the other experimental groups, which showed no marked differences in growth performance.After the experiment, dorsal muscle fluoride concentrations in each group were below the detectable limit (1mgkg−1), but vertebral bone fluoride concentrations increased with increasing proportion of KM to 655 (KM0), 870 (KM15), and 2150 (KM100) mgkg−1. With increasing LFK in the feed, vertebral bone fluoride concentrations (mgkg−1) increased slightly from 500 (LFK0) to 655 (LFK15), and 695 (LFK100). No histopathological changes were detected in the liver tissue in any experimental group.It has been reported that the fluoride bioavailability was reduced with increasing water hardness, however, the dietary fluoride derived from KM exoskeleton accumulates in vertebral bones of marine fish with growth inhibition, as has already been shown for freshwater fish. Vertebral bone fluoride concentrations in two krill-eating Antarctic marine fish in the wild were 33000mgkg−1 (Champsocephalus gunnari) and 15000mgkg−1 (Notothenia rossii), but they did not show any adverse effect of growth. Therefore, fish bone fluoride accumulation apparently depends on fish species rather than the salinity of the habitat. Consequently, krill exoskeleton must be removed during the processing of Antarctic krill if indeed these krill are to be used as fish feed. However, LFK can completely replace dietary fish meal without apparent adverse effects.

Philometra sawara sp. n. and a redescription of Philometra sciaenae Yamaguti, 1941 and Philometra nemipteri Luo, 2001 (Nematoda: Philometridae): a morphological and molecular approach

Morphological data and molecular analyses are used to describe the taxonomy of philometrid nematodes of the genus Philometra Costa, 1845, found in the gonads of marine fishes in Japan. A new Philomnetra species, P. sawara sp. n., is described based on male and female specimens collected from the gonads of Scomberomorus niphonius (Cuvier) (Japanese Spanish mackerel). Two additional species, Philometra nemipteri Luo, 2001 and Philometra sciaenae Yamaguti, 1941, are confirmed as valid species and are redescribed based on specimens collected from the gonads of Nemipterus virgatus (Houttuyn) (golden threadfin bream) and Pennahia argentata (Houttuyn) (silver croaker), respectively. Male P. nemipteri are first reported and described in this study. Redescriptions of female P. nemipteri and male and female P. sciaenae were also necessary based on our morphological observations. A molecular comparison of the internal transcribed spacer 2 (ITS2) region of the ribosomal DNA between P. sawara, P. nemipteri, P. sciaenae, and previously reported philometrid nematodes from the genus Philometra and Philometroides Yamaguti, 1935 supports the conclusion that the three Philometra species in the current study are independent. An ITS2-derived neighbour-joining tree, consisting of both the current specimens and previously described Philometra and Philometroides species, is also presented.

Symposium “Current Topics on Protozoan and Other Parasitic Diseases of Fish in Japan”

The Japanese Society of Fish Pathology held a symposium entitled “Current topics on protozoan and other parasitic diseases of fish in Japan” in Miyazaki on 27th September 2001. This symposium was aimed to have an overview of the current status of the researches on protozoan and other parasitic diseases of fish in Japan. Following a keynote presentation of the same subject in the world, two emerging diseases of marine fish in Japan, i.e. emaciation disease in tiger puffer and anemia in Japanese flounder, were introduced. Three species of myxosporeans are responsible for the former disease, and a monogenean Neoheterobothrium hirame causes the latter. The resent researches on kudoosis amami in yellowtail and amberjack, Heterobothrium infection in tiger puffer and blood fluke disease in yellowtail were also presented. The importance of the prevention against the fish protozoan and other parasitic diseases was discussed.

Observations on five species of philometrid nematodes from marine fishes in Japan

Five species of philometrid nematodes (subfamily Philometrinae) are redescribed on the basis of newly collected materials from marine fishes from Japan. The species Philometra sciaenae Yamaguti, 1941, considered by Rasheed (1963) a synonym of P. lateolabracis (Yamaguti, 1935), is re-established as a valid species and the male of this nematode, collected from the ovary of the type-host, Argyrosomus argentatus, is described for the first time; the latter is characterised mainly by the length of equally long spicules (0.108–0.126 mm) and the length ratio of the gubernaculum and spicules (1:2.25). Other species redescribed on females include Philometra inimici Yamaguti, 1941 and P. sebastisci Yamaguti, 1941 from the ovary of their type-hosts, Inimicus japonicus and Sebastiscus marmoratus, respectively, and also Philometroides seriolae (Ishii, 1931) from the musculature of Seriola quinqueradiata (type-host), and Clavinema mariae (Layman, 1930) from the subcutaneous tissue of Pleuronectes schrenki and Acanthogobius flavimanus (a new host record). For the first time, cephalic ends of some of these species were studied under the scanning electron microscope (SEM) and the character of their cephalic papillae was described. The importance of a knowledge of male morphology for the taxonomy of philometrids is stressed.

Bacterial Diseases of Cultured Marine Fish in Japan.

Many species of pathogenic bacteria have been reported from marine fishes in Japan : Aeromonas salmonicida (atypical), clamydia like organisms (epitheliocystis organisms), Edwardsiella tarda, Flexibacter maritimus, Lactococcus garvieae (syn. Enterococcus seriolicida), Mycobacterium sp., Nocardia seriolae (syn. N. kampachi), Photobacterium damsela subsp. piscicida (syn. Pasteurella piscicida), Pseudomonas anguilliseptica, Pseudomonas putida, Renibacterium salmoninarum (in maricultured salmonids), Staphylococcus epidermidis, Streptococcus equisimilis, Streptococcus iniae, Vibrio alginolyticus, Listonella anguillarum (syn. Vibrio anguillarum), Vibrio ichthyoenteri, Vibrio ordalii, Vibrio trachuri and some other minor or unknown species. These bacteria usually give damages to some limited fish species, however, most of them have been found to be distributed in other cultured and wild fish species which will be possible hosts or carriers of pathogens. Drug resistance, deterioration of water around farms, and spread of pathogens by transporting seedling fish are the major problems for the control of disease in Japanese mariculture.

Viral Diseases in Cultured Marine Fish in Japan.

In Japan, mass mortalities of cultured fish due to infectious diseases have been often reported. Among the pathogens, viruses are the most devastating infectious agents that afflict fish. This paper reviews the major viral diseases of cultured marine fish in Japan. The major diseases caused by DNA viruses include viral epidermal hyperplasia in flounder and herpesviral disease in coho salmon, both caused by a hepesviruses and lymphocystis disease and another iridoviral disease in red sea bream and other marine fishes. The major diseases caused by RNA viruses are viral ascites (VA), viral deformity (VD) in yellowtail, both caused by a birnavirus (YAV or VDV), erythrocytic inclusion body syndrome (EIBS) in coho salmon, a rhabdoviral disease in flounder and viral nervous necrosis (VNN) in striped jack and several other fishes by a nodavirus. The causative virus of Kuchijirosho in tiger puffer has not been classified.

Parasitic Diseases of Cultured Marine Fish in Japan.

Parasitic Diseases of Cultured Marine Fish in Japan.

Culture technology of marine rotifers and the implications for intensive culture of marine fish in Japan

In order to expand the practice of rearing marine finfish larvae, it is necessary to increase and stabilize the production of live feed. Latest researches on rotifer culture technology in Japan have aimed at these objectives. This paper summarizes the progress on the technology of high-density rotifer mass cultures. The high-density culture of the marine rotifer Brachionus rotundiformis (so-called S-type) enables production that is at least 100 times more efficient than that by the conventional method, with less cost for production. The technology is based on the use of highly concentrated algal biomass as food for rotifers. Rotifers are mass-cultured at 10000-30000 individuals mL-1 by feeding them exclusively on condensed freshwater Chlorella. Cultures are generally supplied with constant O2; pH is adjusted to 7 by addition of HCI to avoid an increase of free ammonia in the culture system. The excess suspended organic matter can be efficiently removed by a nylon filtration mat.

Principal microbial diseases of mariculture in Japan

The most important microbial diseases encountered in the rapidly developing mariculture industry of Japan are described. Vibriosis, pseudotuberculosis, streptococcicosis, nocardiosis and bacterial kidney disease (BKD) were the most important bacterial infections, resulting insignificant losses in mariculture fish production. Viral infections with epizootic outbreaks were observed with yellowtail fry and Japanese flounder. In kuruma shrimp culture, problems were caused by vibriosis and a Baculovirus sp. The annual damage and losses due to diseases in mariculture in Japan in 1984 are tabulated. An overview is given of the drugs allowed and used for treatment of diseases of marine fish in Japan.

Flexibacter sp., a gliding bacterium pathogenic to some marine fishes in Japan.

A new bacterial disease, bringing about mass mortality of cultured juvenile red sea bream (Pagrus major) and black sea bream (Acanthopagrus schlegeli) in Hiroshima Prefecture, was found to be due to a kind of gliding bacterium. In the present study, 8 strains of gliding bacteria isolated from diseased juvenile red sea breams and black sea breams were studied on their morphological, biochemical, and physiological characteristics. All strains were gram-negative, flexuous rods which exhibited gliding motility without flagella, and usually about 0.5μm by 2 to 30μm. Filamentous cells measuring up to 100μm in length were occasionally found. The organisms showed no anaerobical growth and did not produce microcysts. They utilized none of the 24 kinds of carbohydrates tested. Polysaccharides such as agar, cellulose, and chitin were not decomposed. The guanine plus cytosine proportional content in the DNA was 31.3 to 32.5%. The organisms grew in media prepared with sea water or a synthetic sea water, but did not in those with NaCl alone. On the basis of these characteristics, it was considered that the present organisms should be placed in the genus Flexibacter. The organism was found to be distinct in its various characteristics and pathogenicity to fish from any formally established species of the genus Flexibacter, and, therefore, it was classified as a new species.