Juvenile semi-wild fish have a higher metabolic rate than farmed fish.

Fish from commercially farmed stocks are often released into the natural environment to supplement wild populations. This practice is often applied to salmonid fish as they are an essential fishery resource and also used for recreational angling. However, farmed fish tend to show lower survival rates after release than wild fish. For this reason, the release of semi-wild fish is increasingly used in Japan; these fish are generated using female fish from domesticated stocks and male fish of wild origin. The survival rate of released semi-wild fish is higher than that of farmed fish, but the reason for this is unknown. This study compared the metabolism and swimming performance of semi-wild and farmed masu salmon (Oncorynchus masou). The analyses showed that resting metabolic rate (RMR), maximum metabolic rate (MMR) and swimming speeds that minimize energy costs of travel (optimal swimming speed) were higher in semi-wild fish than in farmed fish. Critical swimming speed did not differ significantly between the two groups of fish. Semi-wild fish with high RMR may have a social status advantage over farmed fish because a previous study reported that SMR, which is the value closest to basal metabolism significantly affects feeding motivation. This means that individuals with higher social status may be more motivated to feed. As RMR is proportional to food requirements, then release programs should be planned taking food resources at the release site into consideration.

Expression of Doublecortin, Glial Fibrillar Acidic Protein, and Vimentin in the Intact Subpallium and after Traumatic Injury to the Pallium in Juvenile Salmon, Oncorhynchus masou.

Fetalization associated with a delay in development and the preservation of the features of the embryonic structure of the brain dominates the ontogeny of salmonids. The aim of the present study was to comparatively analyze the distribution of the glial-type aNSC markers such as vimentin and glial fibrillar acidic protein (GFAP) and the migratory neuronal precursors such as doublecortin in the telencephalon subpallium of juvenile masu salmon, Oncorhynchus masou, in normal conditions and at 1 week after an injury to the dorsal pallium. Immunohistochemical labeling of vimentin, GFAP, and doublecortin in the pallium of intact juvenile masu salmon revealed single cells with similar morphologies corresponding to a persistent pool of neuronal and/or glial progenitors. The study of the posttraumatic process showed the presence of intensely GFAP-labeled cells of the neuroepithelial type that form reactive neurogenic zones in all areas of the subpallial zone of juvenile masu salmon. A comparative analysis of the distribution of radial glia in the dorsal, ventral, and lateral zones of the subpallium showed a maximum concentration of cells in the dorsal part of subpallium (VD) and a minimum concentration in the lateral part of subpallium VL. An essential feature of posttraumatic immunolabeling in the masu salmon subpallium is the GFAP distribution patterns that are granular intracellular in the apical periventricular zone (PVZ) and fibrillar extracellular in the subventricular (SVZ) and parenchymal zones (PZ). In contrast to those in intact animals, most of the GFAP+ granules and constitutive neurogenic niches in injured fish were localized in the basal part of the PVZ. With the traumatic injury to the subpallium, the number of Vim+ cells in the lateral and ventral regions significantly increased. At 1 week post-injury, the total immunolabeling of vimentin cells in the PVZ was replaced by the granular pattern of Vim immunodistribution spreading from the PVZ to the SVZ and deeper parenchymal layers of the brain in all areas of the subpallium. A significant increase in the number of DC+ cells was observed also in all areas of the subpallium. The number of cells increased both in the PVZ and in the SVZ, as well as in the deeper PZ. Thus, at 1 week after the injury to the dorsal pallium, the number of DC, Vim, and GFAP expressing cells of the neuroepithelial type in the subpallium of juvenile masu salmon increased, and additionally GFAP+ radial glia appeared in VD, which was absent from intact animals.

Production of juvenile masu salmon (Oncorhynchus masou) from spermatogonia-derived sperm and oogonia-derived eggs via intraperitoneal transplantation of immature germ cells.

No effective cryopreservation technique exists for fish eggs and embryos; thus, the cryopreservation of germ cells (spermatogonia or oogonia) and subsequent generation of eggs and sperm would be an alternative solution for the long-term preservation of piscine genetic resources. Nevertheless, in our previous study using rainbow trout, we showed that recipients transplanted with XY spermatogonia or XX oogonia produced unnatural sex-biased F1 offspring. To overcome these obstacles, we transplanted immature germ cells (XX oogonia or XY spermatogonia; frozen for 33 days) into the body cavities of triploid hatchlings, and the transplanted germ cells possessed a high capacity for differentiating into eggs and sperm in the ovaries and testes of recipients. Approximately 30% of triploid recipients receiving frozen germ cells generated normal salmon that displayed the donor-derived black body color phenotype, although all triploid salmon not receiving transplants were functionally sterile. Furthermore, F1 offspring obtained from insemination of the oogonia-derived eggs and spermatogonia-derived sperm show a normal sex ratio of 1:1 (female:male). Thus, this method presented a critical technique for practical conservation projects for other teleost fish species and masu salmon.

Captive-bred populations of a partially migratory salmonid fish are unlikely to maintain migratory polymorphism in natural habitats.

Variation in life history is fundamental to the long-term persistence of populations and species. Partial migration, in which both migratory and resident individuals are maintained in a population, is commonly found across animal taxa. However, human-induced habitat fragmentation continues to cause a rapid decline in the migratory phenotype in many natural populations. Using field and hatchery experiments, we demonstrated that despite both migrants and residents being maintained in captive environments, few individuals of the red-spotted masu salmon, Oncorhynchus masou ishikawae, became migrants in natural streams when released prior to the migration decision. Released fish rarely reached the threshold body size necessary to become migrants in natural streams, presumably owing to lower growth rates in natural than in captive environments. The decision to migrate is often considered a threshold trait in salmonids and other animal taxa. Our findings highlight the need for management programmes that acknowledge the effects of the environment on the determination of the migratory phenotypes of partially migratory species when releasing captive-bred individuals prior to their migratory decisions.

Ascending speed and nocturnal activity of adult masu salmon (Oncorhynchus masou Brevoort) during upstream migration.

We released five adult masu salmon (Oncorhynchus masou) tagged with external transmitters to track their ascending behaviour. The signals of all specimens were recorded in the upper area of the river system. Two patterns of ascending behaviour were recognized: ascending upward immediately after release and ascending during increased river discharge. The fastest ascending speed was about 1000 m h-1 . Active movements were detected at night. The signal recording duration at each receiver for each fish was generally brief. Most fish did not stay at the pools where the receivers were installed.

Hydrogen Sulfide Modulates Adult and Reparative Neurogenesis in the Cerebellum of Juvenile Masu Salmon, Oncorhynchus masou.

Fish are a convenient model for the study of reparative and post-traumatic processes of central nervous system (CNS) recovery, because the formation of new cells in their CNS continues throughout life. After a traumatic injury to the cerebellum of juvenile masu salmon, Oncorhynchus masou, the cell composition of the neurogenic zones containing neural stem cells (NSCs)/neural progenitor cells (NPCs) in the acute period (two days post-injury) changes. The presence of neuroepithelial (NE) and radial glial (RG) neuronal precursors located in the dorsal, lateral, and basal zones of the cerebellar body was shown by the immunohistochemical (IHC) labeling of glutamine synthetase (GS). Progenitors of both types are sources of neurons in the cerebellum of juvenile O. masou during constitutive growth, thus, playing an important role in CNS homeostasis and neuronal plasticity during ontogenesis. Precursors with the RG phenotype were found in the same regions of the molecular layer as part of heterogeneous constitutive neurogenic niches. The presence of neuroepithelial and radial glia GS+ cells indicates a certain proportion of embryonic and adult progenitors and, obviously, different contributions of these cells to constitutive and reparative neurogenesis in the acute post-traumatic period. Expression of nestin and vimentin was revealed in neuroepithelial cerebellar progenitors of juvenile O. masou. Patterns of granular expression of these markers were found in neurogenic niches and adjacent areas, which probably indicates the neurotrophic and proneurogenic effects of vimentin and nestin in constitutive and post-traumatic neurogenesis and a high level of constructive metabolism. No expression of vimentin and nestin was detected in the cerebellar RG of juvenile O. masou. Thus, the molecular markers of NSCs/NPCs in the cerebellum of juvenile O. masou are as follows: vimentin, nestin, and glutamine synthetase label NE cells in intact animals and in the post-traumatic period, while GS expression is present in the RG of intact animals and decreases in the acute post-traumatic period. A study of distribution of cystathionine ß-synthase (CBS) in the cerebellum of intact young O. masou showed the expression of the marker mainly in type 1 cells, corresponding to NSCs/NCPs for other molecular markers. In the post-traumatic period, the number of CBS+ cells sharply increased, which indicates the involvement of H2S in the post-traumatic response. Induction of CBS in type 3 cells indicates the involvement of H2S in the metabolism of extracellular glutamate in the cerebellum, a decrease in the production of reactive oxygen species, and also arrest of the oxidative stress development, a weakening of the toxic effects of glutamate, and a reduction in excitotoxicity. The obtained results allow us to consider H2S as a biologically active substance, the numerous known effects of which can be supplemented by participation in the processes of constitutive neurogenesis and neuronal regeneration.

Assessment of the timing and degree of smolt development in southern populations of masu salmon Oncorhynchus masou.

The present study assessed whether non-anadromous masu salmon Oncorhynchus masou in Miyazaki, southern Japan, smoltify, and if so, at what time of the year. Yearling O. masou of Miyazaki and an anadromous population from Hokkaido, northern Japan, were reared in hatcheries in their respective regions and sampled monthly from February to June to examine the spring smoltification period. The Hokkaido population showed a peak of gill Na+ -K+ -ATPase (NKA) activity in May, which was accompanied with an increase in mRNA levels of the seawater (SW)-type NKA alpha subunit, nkaα1b. Increases in gill NKA activity and nkaa1b levels were not seen in Miyazaki populations. Transferring yearling Miyazaki population to 70% SW (salinity of 23) in mid-April resulted in an increased serum osmolality over 4 days. These results suggest that they do not smoltify in their second spring. Next, profiles of gill NKA activity and its subunit mRNA levels in under-yearling Miyazaki population in the autumn were examined. Two phenotypes differing in body color during this period were categorized as parr and smolt-like fish. Smolt-like fish had higher gill NKA activity than parr in December while there was no significant difference in gill nkaα1b levels. Smolt-like fish acclimated to 70% SW better than parr as judged by lower serum osmolality. However, serum osmolality in smolt-like fish did not return to the basal level 7 days after transfer to 70% SW, suggesting that their hypo-osmoregulatory ability was not fully developed to a level comparable to anadromous populations of this species. The present study suggests that, if O. masou in Miyazaki go though a smoltification process, it occurs in its first autumn instead of the second spring and is less pronounced compared with anadromous populations.

Iteroparity of stream resident masu salmon Oncorhynchus masou.

The degree of iteroparity in stream-resident forms of masu salmon Oncorhynchus masou was examined using mark-recapture studies in natural streams. In a partially migratory population, at least 10% of resident males survived after maturation and repeatedly matured for up to 5 years. In the landlocked amago salmon subspecies, the post-maturation survival rate was at least 7% and repeat maturation was observed for up to 3 years for both males and females.

Long-term (5 years) cryopreserved spermatogonia have high capacity to generate functional gametes via interspecies transplantation in salmonids.

Although sperm cryopreservation is a powerful tool widely applicable in biodiversity conservation and broodstock management, cryopreservation of teleost eggs and embryos remains challenging. In the present study, we demonstrated that spermatogonia of rainbow trout (Oncorhynchus mykiss) cryopreserved for 5 years possessed the ability to differentiate into functional eggs or sperm in the gonads of triploid recipient masu salmon (Oncorhynchus masou). After cryopreservation for 5 years in liquid nitrogen, intraperitoneally transplanted spermatogonia migrated toward, and incorporated into, the gonads of xenogeneic recipients. The transplanted spermatogonia resumed spermatogenesis and oogenesis in male and female recipients, respectively, and differentiated into sperm or eggs within the gonads of male and female recipients at 2 years posttransplantation. The differentiated sperm and eggs generated normal rainbow trout representative of donor phenotypes. Thus, cryopreservation of spermatogonia is a powerful and reliable method for long-term preservation of fish genetic resources.

Radiocaesium concentrations in the muscle and eggs of salmonids from Lake Chuzenji, Japan, after the Fukushima fallout.

Approximately 18 months (September to December 2012) after the Fukushima Dai-ichi Nuclear Power Plant accident, elevated radiocaesium concentrations were measured in samples of muscle and eggs from masu salmon Oncorhynchus masou, kokanee Oncorhynchus nerka, brown trout Salmo trutta and lake trout Salvelinus namaycush from the Lake Chuzenji system, central Honshu Island, Japan (160 km from the station). Mean muscle concentrations were 142·9-249·2 Bq kg⁻¹ wet mass and mean concentrations in eggs were 38·7-79·0 Bq kg⁻¹ wet mass. There was no relationship between fork length and muscle radiocaesium concentration in any of the species, but there were significant relationships between individual muscle and egg radiocaesium concentrations from O. masou, S. trutta and S. namaycush.

Diurnal changes in salmon GnRH secretion in the brain of masu salmon (Oncorhynchus masou).

The day-night changes of salmon GnRH (sGnRH), which is secreted from various brain regions, were analyzed in maturing and matured masu salmon (Oncorhynchus masou). In maturing males, the levels of sGnRH secreted from the olfactory bulb (OB), terminal nerve (TN), and ventral telencephalon and preoptic area (VT+POA) were all significantly higher during midnight than daytime. However, the contents of sGnRH in the pituitary gland during midnight were not higher than those during daytime. In maturing females, the levels of sGnRH secreted from the VT+POA were higher during midnight than daytime, and the contents of sGnRH in the pituitary gland were also higher during midnight. In matured fish, the levels of sGnRH secreted from the OB, TN and VT+POA during midnight were significantly higher than those during daytime. There were also no significant differences in the contents of sGnRH in the pituitary gland. These results suggest that a short photoperiod may be involved in diurnal secretion rhythms of sGnRH in various brain regions and the pituitary gland.

Genetic Distances of Rainbow Trout and Masu Salmon as Determined by PCR-Based Analysis.

This study used a PCR-based genetic analysis platform to create a hierarchical polar dendrogram of Euclidean genetic distances for two salmonid species, Oncorhynchus mykiss (rainbow trout, RT) and Oncorhynchus masou (masu salmon, MS). The species were distantly related to other fish species based on PCR results from using the designed oligonucleotide primer series. Five oligonucleotide primers were used to generate 330 and 234 scorable fragments in the RT and MS populations, respectively. The DNA fragments ranged in size from approximately 50 bp to more than 2,000 bp. The bandsharing (BS) results showed that the RT population had a higher average BS value (0.852) than that for the MS population (0.704). The genetic distance between individuals supported the presence of adjacent affiliation in cluster I (RT 01-RT 11). The observation of a significant genetic distance between the two Oncorhynchus species verifies that this PCR-based technique can be a useful approach for individual- and population-based biological DNA investigations. The results of this type of investigation can be useful for species safekeeping and the maintenance of salmonid populations in the mountain streams of Korea.

Proliferation, Adult Neuronal Stem Cells and Cells Migration in Pallium during Constitutive Neurogenesis and after Traumatic Injury of Telencephalon of Juvenile Masu Salmon, Oncorhynchus masou.

A study of the lateral pallium in zebrafish and the visual tectum of the medaka revealed a population of adult neuroepithelial (NE) cells supported from the early stage of development to various postembryonic stages of ontogenesis. These data emphasize the importance of non-radial glial stem cells in the neurogenesis of adult animals, in particular fish. However, the distribution, cell cycle features, and molecular markers of NE cells and glial progenitors in fish are still poorly understood at the postembryonic stages of ontogenesis. Fetalization predominates in the ontogenetic development of salmon fish, which is associated with a delay in development and preservation of the features of the embryonic structure of the brain during the first year of life. In the present work, we studied the features of proliferation and the migration of neuronal precursors in the pallial proliferative zone of juvenile Oncorhynchus masou. The aim of the study is a comparative analysis of the distribution of glial-type aNSCs markers, such as vimentin and glial fibrillar acid protein GFAP, as well as the proliferation marker BrdU and migratory neuronal precursor doublecortin, in the pallial zone of the intact telencephalon in juvenile O. masou normal and after mechanical injury. The immunohistochemical IHC labeling with antibodies to vimentin, GFAP and doublecortin in the pallium of intact fish revealed single, small, round and oval immunopositive cells, that correspond to a persistent pool of neuronal and/or glial progenitors. After the injury, heterogeneous cell clusters, radial glia processes, single and small intensely labeled GFAP+ cells in the parenchyma of Dd and lateral part of pallium (Dl) appeared, corresponding to reactive neurogenic niches containing glial aNSCs. A multifold increase in the pool of Vim+ neuronal precursor cells (NPCs) resulting from the injury was observed. Vim+ cells of the neuroepithelial type in Dd and Dm and cells of the glial type were identified in Dl after the injury. Doublecortine (Dc) immunolabeling after the injury revealed the radial migration of neuroblasts into Dm from the neurogenic zone of the pallium. The appearance of intensely labeled Dc+ cells in the brain parenchyma might indicate the activation of resident aNSCs as a consequence of the traumatic process.

Polychlorinated biphenyl (PCB) concentrations and congener composition in masu salmon from Japan: a study of all 209 PCB congeners by high-resolution gas chromatography/high-resolution mass spectrometry (HRGC/HRMS).

We collected two subspecies of masu salmon: Oncorhynchus masou masou from four localities (southern Sea of Japan northward to Hokkaido) and O. masou ishikawae from upstream from Ise Bay close to a heavy industrial area. All 209 PCB congeners were analyzed using HRGC/HRMS. PCA ordination of congener concentrations divided data into three groups: (i) ssp. masou from Hokkaido, (ii) ssp. masou from the other regions and (iii) ssp. ishikawae. The highest ∑ PCB concentration (40.39 ng/wet wt) was in ssp. ishikawae followed by ssp. masou from southern waters; however the TEQdioxin-like PCBs was highest in ssp. masou from southern water (1.96 pg-TEQdioxin-like PCBs/g wet wt.) due to the high proportion of congener #126 in its complement (#126 has the highest toxic equivalency factor among congeners). There is likely a contamination source offshore in the southern Sea of Japan and/or along the migratory route of ssp. masou.