Masou Research Articles

Hierarchical genetic structure of native masu salmon populations in Hokkaido, Japan

Identification of the spatial extent of genetic structuring that may be influenced by evolutionary, ecological and historical factors is critical for effective conservation or management strategies. Masu salmon Oncorhynchus masou is commonly distributed in Far East, however, many local populations have been under threats of decline due to habitat destruction, overexploitation, and genetic introgression. To reveal the spatial genetic structure of native masu salmon populations in Hokkaido, masu salmon samples were collected from 16 rivers in which there was no official record of artificial releases of any masu salmon stock and were analyzed using 15 microsatellite loci. A Bayesian assignment test revealed that masu salmon populations were divided into two genetically distinct groups: the northeastern and southwestern groups. For within-group genetic structure, all populations, except for geographically proximate populations, were significantly different from each other. AMOVA revealed that genetic variation at among-group level based on groups identified assignment test was greater than that of groups based on geographic locations. There was no significant IBD for the 16 populations. However, the Mantel test revealed significant IBD for the northeastern group, but did not for the southwestern group. This study suggested that native masu salmon populations in Hokkaido exhibit a hierarchical genetic structure that is largely a result of their precise homing behavior. The results of this study also highlight the importance of defining populations by using genetic data rather than by using predefined populations based on geographic locations for the correct determination of genetic structure.

Distribution of Masu Salmon Oncorhynchus masou (Salmonidae) in Amur River Basin

The presented data on the distribution of the masu salmon Oncorhynchus masou in the Amur River Basin are collected in 1976–2015. In the analyzed region the species’ spawning range includes the lower part of the Amur River basin from the rivers flowing into the Amur estuary to the basins of the Anyui and Amgun’ Rivers in their middle courses. The information on the catch of a masu salmon specimen in the Khor River Basin (approximately 1300 km from the Amur River mouth) in 2015 is presented. It is assumed that the total Amur population does not exceed several thousand of adult anadromous fish.

Experimental evaluation of predation of stocked salmon by riparian wildlife: effects of prey size and predator behaviours

Predation after release is one of the major concerns of hatchery fish conservation and propagation. However, the relationships between the size of hatchery fish, the predator species and their behaviours in natural environments are largely unknown. To understand these relationships, we conducted predation experiments in outdoor tanks and a seminatural stream with exposure to local predators. Masu salmon (Oncorhynchus masou) of two different size classes were used as experimental prey fish in the present study. Camera trap data showed that grey herons (Ardea cinerea) were the primary predator in the experimental system, and that most herons used shallow areas in the morning or evening while feeding. Increasing the density of stocked salmon led to increases in the number of occurrences of grey heron. More importantly, predation by grey herons resulted in a significantly lower survival rate of larger salmon compared with smaller salmon. The results indicate that it is important to understand local predators, adjust the optimum body size of hatchery fish at release and choose the appropriate stocking site and time of day for maximising the effectiveness of fish stocking.

Adoption of alternative migratory tactics: a view from the ultimate mechanism and threshold trait changes in a salmonid fish

Partial migration, in which a portion of the population migrates while the rest of the population remains as residents, is a common form of migration. Alternative migratory tactics (AMTs) of partial migration are often determined by polygenic threshold traits. However, the ultimate mechanisms that drive inter‐population variations in threshold traits are not well understood. We present a simple schematic model to explain how the threshold trait changes with fitness consequences under opposing natural and artificial selection forces. We conducted a field test to evaluate the effects of migration difficulty (as a natural selective force) and selective captive breeding (as an artificial selective force) on threshold traits of a partially migratory fish. Male masu salmonOncorhynchus masouin the Shari River system have AMTs divided into three population categories of hatchery, wild/above the waterfall, and wild/below the waterfall (control). The wild/above the waterfall salmon live in a high‐migration‐cost situation, and the threshold trait changed in a direction that promoted residency. In hatchery salmon, which are produced by migrant‐selective captive breeding, the threshold trait changed in a direction that promoted migration. In contrast, Dolly Varden charrSalvelinus malmadisplayed only resident tactics, and the threshold trait did not differ between the populations above and below the waterfall, indicating that environment did not explain the variation in the threshold trait. Our results support the model and suggest that opposing natural and artificial selection forces drive variations in the threshold traits and migratory patterns in the studied species. Our conceptual framework for the ultimate mechanism may help to better understand adoption of AMTs and production of diverse intraspecific traits in migratory animals.

GFAP and PCNA Marking in the cerebellum of masu salmon’s (Oncorhynchus masou) juvenile after mechanical injury

The objective of this work was to study proliferation processes and the role of glia and neural stem cells in the event of injurious action on cerebellum of masu salmon’s (Oncorhynchus masou) juvenile. Using the immunoperoxidase staining of the glial fibrillary acidic protein (GFAP) and proliferating cells nuclear antigen (PCNA), processes of proliferation and gliogenesis after mechanical trauma of cerebellum of cherry salmon’s (Oncorhynchus masou) juvenile were studied. After the trauma, the intensity of proliferation and migration processes varies in different zones. Proliferation processes decrease after the trauma in lateral and basal zones, and migration increases. In the dorsal zone, on the contrary, migration processes significantly decrease and proliferation increases. In the dorsal matrix zone of a cerebellum, intense cell proliferation was detected. In the dorsal, lateral, and basal zone of the molecular layer of cerebellum after traumatic damage, neurogenic niches containing PCNA and cells, as well as a heterogeneous population of PCNA-cells, were identified. At the location of neurogenic niches, fibers of radial glia and small single intensely or moderately labeled GFAP cells were discovered. As a result of damaging action, GFAP+ fibers of radial glia, which form differently directed radially oriented bundles, appeared in the dorsal matrix zone. Such structural formations have not been discovered in intact animals. We suppose that, after the trauma, structural reconstruction connected with partial spatial reorientation of the radial glia fibers and formation of specific directions for cells formed in this zone occurs in the dorsal matrix zone. As a result of the trauma, in masu salmon’s cerebellum, elements of the radial glia, including both cells possessing typical morphology and cell fragments presented as long radially oriented processes or cell body containing initial fragments of radial fibers, appeared.

Persistent and reparative neurogenesis in the juvenile masu salmon Oncorhynchus masou telencephalon after mechanical injury

A superficially located periventricular proliferative area with PCNA-immunopositive (PCNA+) cells, which corresponds to the pallial periventricular zone (PVZ) of other fish species, including its dorsal, lateral, and medial compartments, is discovered in the telencephalon of the juvenile masu salmon Oncorhynchus masou. The PCNA+ cells are also identified in the parenchyma of the masu salmon intact brain, and their maximum concentration is observed in the medial zone. After a mechanical injury, the zones of induced neurogenesis—neurogenic niches and sites of secondary neurogenesis surrounded by radial glial fibers—appear in the masu salmon telencephalon. The PVZ of the juvenile masu salmon pallium contains clusters of undifferentiated HuCD-immunopositive (HuCD+) neurons. A change in the HuCD+ cell topography is observed in the mechanically injured masu salmon telencephalon, namely, neurogenic niches in the lateral zone and an increase in the cell distribution density and cell migration patterns in the medial zone. A high level of persistent neurogenesis is characteristic of the juvenile masu salmon brain.

Effect of seawater reared on the nutritional composition and antioxidant activity of edible muscle in smoltified-landlocked masu salmon (Oncorhynchus masou masou)

A new system of aquaculture for landlocked masu salmon (Oncorhynchus masou masou) has recently been developed in the southern Kyushu Island, Miyazaki, Japan. In this system, moderately silvering fish (smolt salmon) are artificially transported from the freshwater aquaculture ponds to floating seawater fish preserve, and they are then aquacultured during winter season, starting from December to the following April. As a result, their growth and body mass were greatly increased (total length: 21.25 ± 1.04–37.80 ± 3.71 cm; body weight: 81.75 ± 19.91–632.00 ± 172.42 g; condition factor: 8.45 ± 1.44–11.4 ± 0.74). In addition, There was a marked increase in chemical components such as the lipid contents (35.0 ± 9.4–79.2 ± 6.7 mg/g muscle), α-tocopherol (29.0 ± 17.0–178.6 ± 15.0 μg/g muscle), astaxanthin (0.1 ± 0.1–15.2 ± 8.8 μg/g muscle), and anserine (4.75 ± 0.59–10.32 ± 2.68 mg/g muscle) in the seawater-reared landlocked masu salmon. Furthermore, the antioxidant activity of the water soluble extract from the seawater-reared landlocked masu salmon increased from 480.96 ± 79.295–848.99 ± 182.79 μmol Trolox equivalent/g tissue. This new system that involves a short period of aquaculture in seawater not only promotes the growth of landlocked masu salmon, but may also improve its nutritional components and antioxidant activity.

Are hatchery chum salmon fry a native invader? Direct and indirect effects of stocking salmon fry on stream organisms

Native species may show invasiveness toward a recipient ecosystem through increases in abundance as a result of artificial stocking events. Salmonid species are typical examples of native invaders whose abundance is increased after stocking with hatchery fish. This study evaluated the effects of hatchery chum salmon fry on sympatric wild masu salmon fry, benthic invertebrate prey, and algae, after a single stocking event in Mamachi stream, Hokkaido, northern Japan. The results suggested that the stocked hatchery chum salmon fry decreased the foraging efficiency and growth of the wild masu salmon fry through interspecific competition, and depressed the abundance of Ephemerellidae and total grazer invertebrates (Glossosomatidae, Heptageniidae, and Baetidae) through predation. Also, the hatchery chum salmon fry may increase algal biomass through depression of grazer abundance by predation (top-down effect). These results suggested that a single release of hatchery chum salmon fry into a stream may influence the recipient stream ecosystem.

Incremental analysis of vertebral centra can reconstruct the stable isotope chronology of teleost fishes

Abstract Isotope analysis has high potential for understanding fish ecology and food‐web structure in aquatic ecosystems. The utility of isotope analysis will be greatly improved if we can reconstruct the chronology of several isotopes at multiple growth stages of individual fish. However, no practical methods exist for reconstructing the chronology of light‐element isotopes (e.g. δ13C, δ15N, δ34S, and Δ14C) in teleost fishes. Here, we present and test a new analytical approach for reconstructing the isotopic ratios of light isotopes at multiple life‐stages in teleost fishes. We sampled an anadromous salmon species, masu salmon Oncorhynchus masou (n = 3), along with water from its natal stream and from the ocean. We subdivided the vertebral centra of the salmon equally into 10 sections and extracted bone collagen from each sample. We then measured the stable sulphur isotope ratios of each vertebral section and compared them with δ34S values of the river water and sea water. We also measured the 87Sr/86Sr ratios of otoliths as a reference indicator of salmon migration between fresh water and the ocean. In all samples, the bone section closest to the centre of the centrum had the lowest δ34S values, which were similar to those of fresh water. The δ34S values gradually increased from the centre to marginal sections, finally reaching constant values similar to those of seawater. The 87Sr/86Sr ratios of sagittal otolith sections had significant inter‐individual differences and were consistent with the patterns of variation of the δ34S values of the vertebral sections. Our results show that the vertebral centra of teleost fishes record isotopic information from juvenile to adult life stages. We suggest that our method can provide reproducible isotopic chronology, even in teleost fishes smaller than 50 cm. This method can be used in isoscape studies and in studies of the ecology of marine teleost fishes.

Short‐term temporal instability in fine‐scale genetic structure of masu salmon

Abstract Identifying spatial extent and temporal patterns of population genetic structure is important for understanding evolutionary relationships among local populations and for designing conservation programmes. However, little attention has been devoted to understand whether genetic structure is temporally stable or unstable, and how genetic characteristics may change over time. The goal of this study was to assess the temporal stability of the genetic structure of masu salmon (Oncorhynchus masou). To examine the temporal component of genetic variation in genetic structuring within a river system, we used 810 masu salmon collected from eight tributaries of the Atsuta River, Hokkaido, Japan, over three consecutive years (i.e. 2007–09). We assessed the temporal stability of the genetic structure in 15 microsatellite loci by comparing genetic diversity, effective population size and the relationships between genetic and geographical distances among samples collected from different tributaries and over time. Significant genetic differences were observed among most of the temporal samples collected from the same tributary, and analysis of molecular variance indicated that the temporal component explained about 10 times more of the genetic variation (1.98%) than did the spatial component (0.18%). Isolation by distance (IBD) was detected only in 2009. In addition, a significant correlation in population genetic structure was observed between samples collected in 2008 and those in 2009. In 2007, decomposed pairwise regression analysis identified one population as an outlier population and, following exclusion of the outlier sample, IBD was observed in 2007. This population is small and physically isolated by waterfall, in which the effective population size or effective number of breeders would be expected to be small. We found that fine‐scale genetic structure in masu salmon populations was temporally unstable, due perhaps to genetic drift in small isolated populations, temporal changes in environmental conditions (e.g. drought), and a combination of these factors. This study also highlights that the genetic structure among populations could easily be affected by temporal and/or sampling issues. Studies focused on temporal genetic structuring are likely to be important for conservation of species inhabiting unstable or isolated habitats such as freshwater fish.

Production of recombinant salmon insulin-like growth factor binding protein-1 subtypes

Insulin-like growth factor (IGF)-I is a growth promoting hormone that exerts its actions through endocrine, paracrine and autocrine modes. Local IGF-I is essential for normal growth, whereas circulating IGF-I plays a crucial role in regulating the production and secretion of growth hormone (GH) by the pituitary gland. These actions of IGF-I are modulated by six insulin-like growth factor binding proteins (IGFBPs). In teleosts, two subtypes of each IGFBP are present due to an extra round of whole-genome duplication. IGFBP-1 is generally inhibitory to IGF-I action under catabolic conditions such as fasting and stress. In salmon, IGFBP-1a and -1b are two of three major circulating IGFBPs and assumed to affect growth through modulating IGF-I action. However, exact functions of salmon IGFBP-1 subtypes on growth regulation are not known due to the lack of purified or recombinant protein. We expressed recombinant salmon (rs) IGFBP-1a and -1b with a fusion protein (thioredoxin, Trx) and a His-tag using the pET-32a(+) vector expression system in Escherichia coli. Trx.His.rsIGFBP-1s were isolated by Ni-affinity chromatography, enzymatically cleaved by enterokinase to remove the fusion partners and further purified by reversed-phase HPLC. We next examined effects of rsIGFBP-1a and -1b in combination with human IGF-I on GH release from cultured masu salmon (Oncorhynchus masou) pituitary cells. Unexpectedly, IGF-I increased GH release and an addition of rsIGFBP-1a, but not rsIGFBP-1b, restored GH levels. The results suggest that IGFBP-1a can inhibit IGF-I action on the pituitary in masu salmon. Availability of recombinant salmon IGFBP-1s should facilitate further functional analyses and assay development.

Community responses to dam removal in a subtropical mountainous stream

Dam removal has the potential to efficiently solve the problems caused by fragmented stream habitats but may simultaneously cause negative impacts on biotic communities. To conserve the critically endangered Formosan landlocked salmon (Oncorhynchus masou formosanus), a 15-m-tall check dam was partially removed from the Chichiawan Stream at the end of May 2011, before the flood season. Using this dam removal experience, we aimed to cast dam removal as an action comparable to a natural flood event. We applied a before-after-control-impact (BACI) design and quantified the environmental factors and major biotic communities at four sampling sites in the stream bimonthly before (2010) and after (2012 and 2013) the dam removal and monthly in the year of the dam removal (2011). After the dam removal, a faster current velocity and more turbid water were observed at the downstream sites, and the area’s deposition consisted of small-grained sediments. Despite this, our results show that the dam removal was performed during a suitable period. There was no obvious influence on tadpoles as they metamorphosed into adult frogs and left the stream before the dam removal. Fish exhibited a greater resistance to the alteration in flow resulting from the dam removal. An increase in fish abundance at the upstream sites after the dam removal suggests that the corridors created by the dam removal allowed access to more habitats for the fish. In particular, the periphyton biomass and aquatic insect densities decreased markedly at the downstream sites after the dam removal, but they recovered within a year, demonstrating the resilience of these taxa. Coleoptera, Plecoptera and Trichoptera were more resistant than the periphyton, Diptera and Ephemeroptera after the dam removal and an extreme flood event. In conclusion, the responses of stream communities to dam removal were similar to the responses to an extreme flood event. To mitigate the impacts caused by dam removal, our results suggest that stream communities may respond to dam removal as a natural flow alteration if the timing of the dam removal occurs just before the flood season.

Sexual size dimorphism in a landlocked Pacific salmon in relation to breeding habitat features

Many animal species exhibit size dimorphism between sexes. Sexual selection, whereby male–male competition favors larger body sizes, has been considered a likely cause of sexual size dimorphism. Habitat features in breeding areas could affect the outcome of male–male competition, yet few attempts have been made to relate breeding habitat features with interpopulation variation in sexual size dimorphism. In this study, we examined interpopulation variation in sexual size dimorphism by studying the landlocked amago salmon (Oncorhynchus masou ishikawae) at a microgeographic scale. We found that female body size was independent of stream size but that male body size decreased with smaller stream sizes. A likely explanation is that the relationship between reproductive success and the size of males is influenced by the availability of refuges that are only available to small-bodied males. Sexual differences in body size increased with decreasing stream sizes, supporting the hypothesis that the reproductive success of larger males is reduced in smaller streams. In contrast, the maturation-length threshold increased with stream size for both sexes. The stream-size-based interpopulation variation in sexual size dimorphism and size at maturity in landlocked amago salmon may therefore have arisen through a combination of sexual and natural selection.

Reproduction efficiency and some characteristics of the spawning grounds of the pink salmon Oncorhynchus gorbuscha in the small salmon watercourse in southern Sakhalin

The peculiarities of the distribution of the freshwater ichthyofauna, bottom sediments and conditions at the spawning grounds, and the egg survivability rate of Oncorhynchus gorbuscha were studied in 2003−2012 in a typical salmon river on Sakhalin Island (Goluboi Ruchei brook, Aniva Bay, southern Sakhalin). The sites characterized by the highest survivability rate of the embryos of the pink salmon are inhabited by the freshwater fish community where the juveniles of masu salmon O. masu and whitespotted char Salvelinus leucomaenis dominate. The lengthway bed slope at this site is steeper compared to the sites with lower survivability rates (0.010−0.020 vs. 0.004−0.020‱). The maximal positive correlation of the egg survivability rate to the flow velocity of the underflow has been registered for the depth of 30−40 cm, and the maximal negative correlation of the egg survivability rate has been registered to the bottom sediment temperature.

Feeding of young masu salmon <i>Oncorhynchus masou</i> in the base river of the Aniva hatchery (southern Sakhalin) after release of the hatchery juveniles

Feeding of masu parr in the natural river habitat on 8-9 days after their release from hatchery is considered on the data obtained in the Lyutoga River tributaries in 2014-2015. No fish with empty stomach were found that indicated successful transition of artificially hatched fish to feeding in the natural environments. More than 40 species of prey were found in their stomachs, mostly terrestrial and aerial invertebrates and the river bottom dwellers as mayflies and chironomids. The diet corresponded to biotopes features. For better feeding (higher stomach filling) gradual releasing is recommended over wide areas by the parties no more than 4,000 ind. The juveniles should be transported in isothermic boxes to the lower or middle parts of streams and in packages with oxygen (for 600-1000 ind. each) to the upper streams. Involving of volunteers from fishermen to the releasing is desirable that attracts additional attention to the species protection.

A delayed effect of the aquatic parasite Margaritifera laevis on the growth of the salmonid host fish Oncorhynchus masou masou

Parasitic species often have detrimental effects on host growth and survival. The larvae of the genus Margaritifera (Bivalvia), called glochidia, are specialist parasites of salmonid fishes. Previous studies have reported negligible influences of the parasite on their salmonid hosts at natural infection levels. However, those studies focused mainly on their instantaneous effects (i.e., during the parasitic period). Given the time lag between physiological and somatic responses to pathogen infections, the effect of glochidial infection may become clearer during the post-parasitic period. Here, we examined whether the effect of glochidial infections of Margaritifera laevis on its salmonid host Oncorhynchus masou masou would emerge during the post-parasitic period. We performed a controlled aquarium experiment and monitored fish growth at two time intervals (i.e., parasitic and post-parasitic periods) to test this hypothesis. Consistent with previous observations, the effects of glochidial infection were unclear in the middle of the experiment (day 50; parasitic period). However, even with a natural glochidial load (48 glochidia per fish), we found a significant reduction in growth rates of infected fish in the extended period of the experiment (day 70; post-parasitic period). Our results suggest that examining only instantaneous effects may provide misleading conclusions about mussel–host relationships.

The complete mitochondrial genome of Oncorhynchus masou formosanus (Salmoniformes: Salmonidae) and phylogenetic studies of Salmoninae

The Formosan landlocked salmon (Oncorhynchus masou formosanus) is at a high risk of extinction and listed as critically endangered species due to the declines in its abundance, overfishing, altered native habitats and its narrow range distribution. Here, we described the complete mitogenome of O. masou formosanus, which is 16,648 bp in length, containing 13 protein-coding genes, two rRNA genes, 22 tRNA genes, a putative control region (CR) and one origin of replication on the light-strand (OL). The overall base composition is 28.6% A, 26.8% T, 28.1% C and16.4% G, respectively. All the protein-coding genes use the initiation codon ATG except COI uses GTG. Most of them have TAA or TAG as the stop codon, except COII, ND3, ND4 and Cyt b use an incomplete stop codon T. A phylogenetic tree involving all the Salmoninae species available was constructed to provide relationship within Salmoninae and further conservation strategies for this species.

Genetic differentiation and the problems of conservation of masu salmon (Oncorhynchus masou Brevoort, 1856 (Pisces: Salmonidae)) populations

This study focuses on the strategy for the conservation of masu salmon, Oncorhynchus masou, in the northern part of the species range (via the masu populations in Sakhalin Oblast), based on data of its population structure. It is shown that masu populations that inhabit different rivers genetically differ from each other in allele frequencies at microsatellite markers. In the Naiba River basin, at least two genetically distinct masu populations exist: in the upper reaches and in a tributary, the Bolshoy Takoy River. The masu populations on Iturup Island significantly differ from those on Sakhalin Island; within Sakhalin, the masu salmon from the Chernaya River in the southwestern part of the island is genetically distinct from the southeastern Sakhalin and Aniva Bay populations. The genetic diversity of Iturup populations is substantially lower than that on Sakhalin, probably due to their small sizes. The measures for the conservation and recovery of masu salmon populations should be based primarily on their own genetic resources, or, in the case of a lack of spawners, on the base populations of their ecological/geographical region. In the latter case, masu populations of large rivers can be considered as base ones: for southeastern Sakhalin, this is masu salmon of the Naiba River; for Aniva Bay, this is masu salmon of the Lyutoga River. Transplantation of fish, fertilized eggs, or any other genetic material from a population that is different genetically and inhabits the waters with different ecological gradients should be strongly restricted. The formosan masu salmon from Taiwan Island is studied as an example of a strict genetic isolate.

Ⅲ-4. ヤマメのミトコンドリアDNAにおける塩基配列に対する影響

Ⅲ-4. ヤマメのミトコンドリアDNAにおける塩基配列に対する影響

アマゴのスモルト化決定の主要因は体サイズである

アマゴのスモルト化決定の主要因は体サイズである