The lateral line system and its innervation in the masu salmon Oncorhynchus masou masou (Salmonidae)

Ichthyological Research - The lateral line system and its innervation were examined in the masu salmon Oncorhynchus masou masou. The species has 8 cephalic canals (supraorbital, infraorbital, otic,...     

Molecular cloning and characterization of three distinct choriogenins in masu salmon, Oncorhynchus masou

Three cDNAs, each encoding a different choriogenin (Chg), were isolated from a female masu salmon (Oncorhynchus masou) liver cDNA library. Two of the cDNA clones, Chg Halpha and Chg Hbeta, showed a close relationship and contained the typical domains of zona pellucida (ZP) B genes in fish, namely proline and glutamine rich repeats, a trefoil factor family domain, and a ZP domain. Specific antibodies against recombinant Chg H products (rmHalpha and rmHbeta) were generated to elucidate the relationship between the Chg H cDNAs and two types of serum Chg H protein, which were previously purified and characterized, and designated as very-high-molecular-weight vitelline envelope-related protein (vhVERP) and Chg H of masu salmon. The immunobiochemical analyses revealed that the Chg Halpha and Chg Hbeta clones encoded vhVERP and Chg H proteins, respectively. The third cDNA clone (Chg L) appeared to be a ZPC gene and, by mapping the N-terminal sequence of purified Chg L, was shown to encode serum Chg L protein. Various types of heteromultimer of the three Chgs were identified immunologically as high molecular weight chorion components, indicating the involvement of complex heterodimerization of multiple Chgs in the construction of chorion architecture in masu salmon.     

Two new species of Myxozoa, Myxobolus inaequus sp. n. and Henneguya theca sp. n. from the brain of a South American knife fish, Eigemannia virescens (V.)

Two new species of Myxozoa from the brain of the green knife fish Eigemannia virescens are described: Myxobolus inaequus sp. n. has an unusually large spore body and extremely unequal polar capsules, and Henneguya theca sp. n. has an attenuated spore encased in a sheath not previously described in other Myxozoa . Only spores of the two species were observed, and infections caused no obvious pathological changes in the brain.     

Effects of external and surgically implanted dummy radio transmitters on mortality, swimming performance and physiological status of juvenile masu salmon Oncorhynchus masou

The effects of external and surgically implanted radio transmitters on juvenile masu salmon Oncorhynchus masou were examined. External attachment of transmitters significantly decreased the survival of fish and caused a decreased critical swimming speed compared with surgical implantation. Although plasma cortisol, plasma glucose and haematocrit values did not differ significantly among groups, it appeared that the most suitable transmitter attachment method for juvenile O. masou may be surgical implantation.     

A visceral mycosis in cultured masu salmon (Oncorhynchus masou) caused by a species of Ochroconis

Ochronconis sp. infection was found in masu salmon (Oncorhynchus masou) with visceral mycosis in Japan. The external and internal clinical signs were reddening of the anal area, swelling of the abdomen due to accumulation of ascitic fluid in the abdominal cavity and extensive swelling of the posterior kidney. Many pale brown, septate hyphae were found in the kidney by direct microscopical examination; these were usually not found in the other organs of infected fish. Histopathological examination of the kidney revealed large granulomas with the fungal hyphae and giant cells. The isolated fungus was identified as a species of the genus Ochroconis and was compared with O. tshawytschae, a known fish pathogen. Based on morphological and growth characteristics, we believe that these cases resulted from infection with a different species.     

Occurrence of a hybrid between endemic Miyabe charr Salvelinus malma miyabei and introduced masu salmon Oncorhynchus masou masou in the Lake Shikaribetsu system, Hokkaido, Japan

A hybrid specimen between endemic Miyabe charr Salvelinus malma miyabei and introduced masu salmon Oncorhynchus masou masou was collected in an inlet stream (Yamada Creek) of the Lake Shikaribetsu. This specimen showed intermediate external characteristics between two species and was also confirmed as a hybrid by DNA markers. The mtDNA of the specimen was identical with that of S. malma miyabei, suggesting that the mating occurred between a female Miyabe charr and a male masu salmon. Hybridization with introduced masu salmon may cause deleterious effects on S. malma miyabei.     

New polymorphic microsatellite markers for the masu salmon (Oncorhynchus masou masou) from Korea and their application to wild and hatchery populations

Masu salmon, Oncorhynchus masou masou, is an economically important fish species in the Far East and occurs in two life history forms: sea-run migratory (anadromous) and freshwater resident (non-anadromous). The non-anadromous form has recently become a popular freshwater food and game fish during a well-known Korean winter festival. However, the genetic background of this species remains largely unknown, partly due to a lack of molecular genetic markers. In this study, we developed new polymorphic microsatellite markers for masu salmon using next-generation sequencing technology. From 40 primer sets, 11 primer sets (27.5% of the primer sets selected) were successfully amplified with 106 alleles (range 2–9) in 64 individuals from different populations: two wild and one hatchery. Observed and expected heterozygosities ranged from 0.304 to 0.947 and 0.278 to 0.865, respectively. Significant departures from the Hardy–Weinberg equilibrium were detected for four markers (OMM11, OMM17, OMM28, and OMM33) in a single population. All pair-wise F_ST values were highly significant between the wild and hatchery populations (range 0.084–0.183, P < 0.0001). We identified a set of robust microsatellite markers that worked well even in formalin-fixed samples, which will be suitable for biogeographical and population structure analyses of the masu salmon.     

Two New Species of Myxozoa, Myxobolus inaequus sp. n. and Henneguya theca sp. n. from the Brain of a South American Knife Fish, Eigemannia virescens (V.)

Two new species of Myxozoa from the brain of the green knife fish Eigemannia virescens are described: Myxobolus inaequus sp. n. has an unusually large spore body and extremely unequal polar capsules, and Henneguya theca sp. n. has an attenuated spore encased in a sheath not previously described in other Myxozoa. Only spores of the two species were observed, and infections caused no obvious pathological changes in the brain.     

Restricted movement of the fluvial form of red-spotted masu salmon,Oncorhynchus masou rhodurus,in a mountain stream,Central Japan

Movement of the fluvial form of red-spotted masu salmon (1⁺ and older),Oncorhynchus masou rhodurus, was studied using mark-recapture methods in a Japanese mountain stream. Most (63–91%) adult salmon were recaptured in the pool in which they were marked. The rest of the salmon moved upstream or downstream <20m during the non-breeding period. The proportion of the salmon moving increased slightly during the breeding period, but did not exceed 66%. The distance moved was also more variable during this period. The proportion of the smaller salmon which moved was larger than that of the larger fish during the non-breeding period. Conversely, during the breeding period, larger fish moved more frequently. Sedentary behaviour and local movements of adult salmon seem to be affected by their social relationships.     

A new species of Myxozoa, Henneguya rondoni n. sp. (Myxozoa), from the peripheral nervous system of the Amazonian fish, Gymnorhamphichthys rondoni (Teleostei)

Henneguya rondoni n. sp. found in the peripheral lateral nerves located below the two lateral lines of the fish Gymnorhamphichthys rondoni (Teleostei, Rhamphichthyidae) from the Amazon river is described using light and electron microscopy. Spherical to ellipsoid cysts measuring up to 110 microm in length contained only immature and mature spores located in close contact with the myelin sheaths of the nervous fibres. Ellipsoidal spores measured 17.7 (16.9-18.1)-microm long, 3.6 (3.0-3.9)-microm wide, and 2.5 (2.2-2.8)-microm (n=25) thick. The spore body measuring 7.0 (6.8-7.3)-microm long was formed by two equal symmetric valves, each with an equal tapering tail 10.7 (10.3-11.0) microm in length. The tails were composed of an internal dense material surrounded by an external homogeneous sheath of hyaline substance. The valves surrounded two equal pyriform polar capsules measuring 2.5 (2.2-2.8)-microm long and 0.85 (0.79-0.88)-microm (n=25) wide and a binucleated sporoplasm cell containing globular sporoplasmosomes 0.38 (0.33-0.42) microm (n=25) in diam. with an internal eccentric dense structure with half-crescent section. Each polar capsule contains an anisofilar polar filament with 6-7 turns obliquely to the long axis. The matrix of the polar capsule was dense and the wall filled with a hyaline substance. The spores differed from those of previously described species. Based on the ultrastructural morphology of the spore and specificity to the host species, we propose a new species name H. rondoni n. sp.     

Fine structure of the myxosporean,Henneguya curimata n. sp., parasite of the Amazonian fish,Curimata inormata (Teleostei,Curimatidae)

Henneguya curimata n. sp. (Myxozoa, Myxobolidae) is described from the kidney of the teleost Curimata inormata collected in an estuarine region of the Amazon River, near Belém. Brazil. This myxosporean produces large cysts (0.6-1.2 mm in diam.) that represent plasmodia containing all life cycle stages, including spores. The spore body is ellipsoidal (approximately 16.6 microm in length and approximately 6.2 microm in width), and each valve presents a tapering tail (approximately 19.1 microm in length). These valves surround the binucleate sporoplasm cell and two ellipsoidal polar capsules located side-by-side at the same level, measuring 6.5 x 1.2 microm each and containing 10-11 coils of the polar filament. On the basis of its host specificity and on data collected by light and electron microscopy, the organism, H. curimata n. sp. is distinguished as a new species. The taxonomic affinities and morphological comparisons with other similar species of the same genus are discussed.     

Henneguya schizodon n. sp. (Myxozoa, Myxobolidae), a parasite of the Amazonian teleost fish Schizodon fasciatus (Characiformes, Anostomidae)

A new histozoic species of myxosporean (Henneguya schizodon n. sp.) is described from the Amazon River teleost fish Schizodon fasciatus Spix & Agassiz, 1892 (Characiformes, Anostomidae). The plasmodia, which showed asynchronous development, were located in the kidney of the host. The spore body was ellipsoidal and was 13.1 (12-14) micron long by 3.3 (3-4) micron wide. The total length of the spore was 28.9 (27-30) micron, and each value had a caudal process measuring 16.3 (15-17) micron. The polar capsules were 5.4 (5-6) micron long by 1.3 (1-1.5) micron wide, and each had a polar filament with 8-10 coils. The characteristics of the species were compared with nearly all the species described so far, including all the species reported from South American fishes. This comparison allows to consider the materials as a new species, and the name Henneguya schizodon n. sp. is proposed.     

Proteomic analysis of inviable salmonid hybrids between female masu salmon Oncorhynchus masou masou and male rainbow trout Oncorhynchus mykiss during early embryogenesis

Early embryos of inviable hybrids between female masu salmon Oncorhynchus masou masou and male rainbow trout Oncorhynchus mykiss at 9, 12, 15 and 20 days after fertilization were examined for protein expression profiles. A total of 44 proteins, mostly down-regulated products of house-keeping genes and those involved in nucleic acid metabolism or chromatin replication, were identified in hybrid embryos by mass spectrometry analysis and protein database searching. The identified down-regulated proteins may be responsible for the inviability in the hybrids.     

Sympatric, simultaneous, and random mating between markless trout (iwame; Oncorhynchus iwame) and red-spotted masu salmon (amago; Oncorhynchus masou ishikawae)

The markless trout (iwame, Oncorhynchus iwame) has long been suspected not to be an independent species, but rather a markless mutant form of the red-spotted masu salmon (amago, O. masou ishikawae). Nevertheless, no field study has examined this issue. Here we report a field study on the reproductive ecology of iwame and amago coexisting in the upper stream of the Inabe River. We found that iwame and amago mate sympatrically, simultaneously, and randomly, and observed five cases of heterogeneous oviposition between the two. Our results suggest that no pre-mating reproductive isolation exists between iwame and amago. Because previous studies have shown the absence of post-mating isolation, we propose that iwame and amago are the same species. Iwame should be considered as a markless form of the red-spotted masu salmon, and O. iwame as a junior synonym of O. masou ishikawae.     

Differences of tributyltin accumulation in the masu salmon Oncorhynchus masou between sea‐run and freshwater‐resident types

In order to examine the accumulation pattern of tributyltin (TBT) in relation to the migratory pattern, TBT concentrations in muscles and strontium (Sr) concentrations in otoliths were determined in both sea‐run and freshwater‐resident masu salmon Oncorhynchus masou . Both TBT and Sr concentrations in sea‐run masu salmon were significantly higher than those of freshwater‐residents.     

Myxobolus albi n. sp. (Myxozoa) from the Gills of the Common Goby Pomatoschistus microps Krøyer (Teleostei: Gobiidae)

ABSTRACT. A recent investigation into the myxozoan fauna of common gobies, Pomatoschistus microps , from the Forth Estuary in Scotland, revealed numerous myxosporean cysts within the gill cartilage. They were composed of polysporous plasmodia containing myxobolid spores that were morphologically different from the other known species of Myxobolus and from the myxosporeans previously recorded from this host (i.e. the ceratomyxid Ellipsomyxa gobii , infecting the gall bladder, and the kudoid Kudoa camarguensis , infecting the muscle tissues). Spores were ovoid, 9.4 × 9.1 μm with a thickness of 6.6 μm, with two pyriform polar capsules, the polar filaments of which had four to five turns. Molecular analysis of the parasite's small subunit rDNA region, based upon a contiguous sequence of 1,558 base pairs, discriminated it from other myxosporean species that have been characterized so far. A comparison of the spore morphology and the molecular sequences determined for this new isolate with other myxozoans described to date, confirmed its identity as a previously unknown myxobolid supporting the proposal that this isolate be elevated to the species level as a new species within the genus Myxobolus . A phylogenetic analysis places this new myxobolid, Myxobolus albi n. sp., in a basal position of a clade containing the majority of Henneguya spp. sequenced to date and various Myxobolus spp.     

Species-dependent migration of fish hatching gland cells that commonly express astacin-like proteases in common

Two constituent proteases of the hatching enzyme of the medaka ( Oryzias latipes ), choriolysin H (HCE) and choriolysin L (LCE), belong to the astacin protease family. Astacin family proteases have a consensus amino acid sequence of HExxHxxGFxHExxRxDR motif in their active site region. In addition, HCE and LCE have a consensus sequence, SIMHYGR, in the downstream of the active site. Oligonucleotide primers were constructed that corresponded to the above-mentioned amino acid sequences and polymerase chain reactions were performed in zebrafish ( Brachydanio rerio ) and masu salmon ( Oncorynchus masou ) embryos. Using the amplified fragments as probes, two full-length cDNA were isolated from each cDNA library of the zebrafish and the masu salmon. The predicted amino acid sequences of the cDNA were similar to that of the medaka enzymes, more similar to HCE than to LCE, and it was conjectured that hatching enzymes of zebrafish and masu salmon also belonged to the astacin protease family. The final location of hatching gland cells in the three fish species: medaka, zebrafish and masu salmon, is different. The hatching gland cells of medaka are finally located in the epithelium of the pharyngeal cavity, those of zebrafish are in the epidermis of the yolk sac, and those of masu salmon are both in the epithelium of the pharyngeal cavity and the lateral epidermis of the head. However, in the present study, it was found that the hatching gland cells of zebrafish and masu salmon originated from the anterior end of the hypoblast, the Polster, as did those of medaka by in situ hybridization. It was clarified, therefore, that such difference in the final location of hatching gland cells among these species resulted from the difference in the migratory route of the hatching gland cells after the Polster region.     

Studies on Myxosoma cartilaginis n. sp. (Protozoa: Myxosporidea) of Centrarchid Fish and a Synopsis of the Myxosoma of North American Freshwater Fishes

SYNOPSIS. Myxosoma cartilaginis n. sp. is described from the cartilage of Lepomis macrochirus (bluegill), L. cyanellus (green sunfish) and Micropterus salmoides (largemouth black bass). The development of the parasite is described from naturally infected fish which were held in spore-free water after infection. The sporoplasm invades cartilage, and becomes a multi-nucleate trophozoite which forms pansporoblasts, each of which produces 2 to 4 spores. The first spores appear in 7 weeks.
The histopathology in the above fish consists at first of little cellular reaction, but after 4 to 5 months epithelioid granulomas appear around some of the spore masses. Cartilage liquefaction is present around the parasites for at least 5 weeks. Eosinophilic globules are present in cartilage cells adjacent to the lesions. Diffuse infiltration of the spores from the lesions is described.
Of 24 chemicals tested for polar filament extrusion, potassium hydroxide gave the best results.
An illustrated synopsis of the Myxosoma of North American fishes is given. Included is some additional information and illustrations of M. hoffmani Meglitsch, 1963. Also included is a table showing the hosts, site of infection, geographic location, spore and polar capsule sizes.     

Relationship between eyed-egg percentage and levels of cortisol and thyroid hormone in masu salmon Oncorhynchus masou

A possible cause of the low eyed-egg percentage that afflicts pond-reared masu salmon Oncorhynchus masou at a fish hatchery (Kumaishi Fish Hatchery, Hokkaido, Japan) was investigated. Serum cortisol levels of masu salmon during the spawning period were compared between individuals from Kumaishi and those from another station (Mori). Cortisol, thyroxine (T₄) and triiodothyronine (T₃) hormones were also measured in eyed eggs and their levels were compared to the eyed-egg percentage. Serum cortisol levels were significantly higher at Kumaishi than at Mori in May and July of the breeding season. At the Kumaishi station, there was a linear positive relationship between serum cortisol and fertilized-egg cortisol levels of female masu salmon. As cortisol levels in both ovulating females and eyed eggs increased, the eyed-egg percentage decreased, indicating a highly significant negative relationship between cortisol levels and eyed-egg percentage. In contrast, as T₃ and T₄ levels in eyed eggs increased, the eyed-egg percentage increased. The strong positive correlation between high cortisol levels in serum and in eyed eggs at Kumaishi indicates that the frequently higher cortisol levels may have caused the lowering of the eyed-egg percentage.     

Effect of paternal life-history form and egg size on offspring life-history traits in masu salmon Oncorhynchus masou

Hydrobiologia - To clarify the effect of paternal life-history form and egg size on offspring life-history traits (e.g., growth and maturation) in masu salmon (Oncorhynchus masou), we studied an...