Masou Research Articles

Long-term response of trophic structure and function to dam removal in a subtropical mountain stream

Although dam removal has been considered a viable strategy to mitigate habitat fragmentation within a stream, long-term ecosystem effects after dam removal have rarely been discussed. In an effort to enhance the resilience of the critically endangered Formosan salmon (Oncorhynchus masou formosanus) in response to climate change, a 15-m-high check dam in a subtropical high-mountain stream was half-removed. The aim of this study was to analyze the long-term response of trophic structure and function to dam removal by constructing Ecopath models upstream and downstream of the removed dam at different times. Field surveys for model parameters were conducted for a complete seasonal cycle 1 year before dam removal, 1 and 2 years (short-term) after dam removal and 7 and 8 years (long-term) after dam removal. Both upstream and downstream systems moved toward maturity after dam removal. In the short term after dam removal, more energy can be transferred further up in the food webs. The vitality and diversity of both systems also increased. In the long term after dam removal, although the transfer efficiencies of both systems generally showed a decreasing pattern, the resilience increased. Compared to the upstream system, the effects of dam removal on the downstream system were more evident. In the downstream system, dam removal enhanced the vitality of the Formosan salmon and thus the top-down control. The dominance of detritivory flow in the food web also shifted toward the dominance of herbivory flow. Consequently, the downstream system reached more maturity, and the food web was more closely linked. The ecosystem attributes of the upstream and downstream systems converged, suggesting that the decoupling between upstream and downstream systems resulting from damming disappeared 8 years after dam removal.

Amphipoda in the diet of nekton in the Okhotsk Sea

Amphipods (mainly hyperiids) are among the top-five taxonomic groups in the diet of many nekton species. Feeding of 106 nekton species dwelled in the Okhotsk Sea is considered (though 93 % of the stomach samples were collected from only 20 mass species). Amphipods are found in the food of 83 species and are absent for 23 species. Taxonomic composition of Amphipoda coincides in plankton and stomach samples; 3 species of hyperiids dominate here and there: Themisto pacifica, T. libellula, Primno macropa. The portion of amphipods in food is the highest for fish with length of 30–40 cm, decreases for smaller and larger fish, and practically disappears for fish with the length > 60 cm. In the food of mass commercial fish species, as pollock, cod, herring, silverfish, char, and pink, chum, sockeye and cherry salmon, the portion of hyperiids in the food could be almost 100 %, with CI of 200–700 ‱. During the daytime, the portion of large-sized hyperiids decreases up to 3 times, as they descend deeper than 200 m. T. pacifica have the highest biomass in the southern Okhotsk Sea, with a long-term tendency to increasing, and the lowest biomass in the northern Okhotsk Sea, with a tendency to decreasing both in the northern and central parts of the sea. P. macropa have similar spatial patters of distribution, but dynamics of their biomass has negative trend in the northern part, positive trend in the central part, and no trend in the southern part of the sea. On the contrary, the biomass of T. libellula is the highest in the northern Okhotsk Sea.

Size-driven parr-smolt transformation in masu salmon (Oncorhynchus masou)

Anadromous salmonids exhibit partial migration, where some individuals within a population migrate down to the ocean through complex interactions between body size and photoperiod. This study aimed to integrate the ontogenetic and seasonal patterns of smoltification, a series of changes for future marine life, in a strain of masu salmon (Oncorhynchus masou). Spring smoltification, as evidenced by the activation of gill Na+,K+-ATPase (NKA), was induced during winter under an advanced photoperiod. In addition, juveniles showed an additional peak in gill NKA activity in August regardless of the photoperiod. When juvenile masu salmon were subjected to feeding manipulations during the first spring/summer, only fish exceeding a fork length of 12 cm exhibited an increased gill NKA activity. We tested whether size-driven smoltification required a long-day period by exposing juveniles to a constant short-day length (9-h light and 15-h dark) from January to November. Juveniles under short-day conditions exceeded 12 cm in June but showed no signs of smoltification. Thus, masu salmon undergo photoperiod-limited, size-driven smoltification during the first summer and size-limited, photoperiod-driven smoltification the following spring. The findings of the present study provide a framework for further elucidation of the physiological mechanisms underlying partial migration in salmonids.

DNA Identification of Parasitic Copepods <i>Salmincola</i> (Copepoda, Siphonostomatoida, Lernaeopodidae): Variability and Rate of Evolution of the Mitochondrial Cytochrome c Oxidase Subunit I Gene

The barcode fragment of the COI gene was sequenced in 91 specimens of five species of parasitic Salmincola copepods, sampled from salmonids mainly from the Russian Far East: S. californiensis (mykiss and masu salmon) and S. edwardsii (various species of chars, sockeye salmon from Lake Kronotskoe), S. carpionis (various species of chars), S. markewitschi (whitespotted char), S. stellata (Sakhalin taimen). A total of 41 haplotypes were found with a maximum level of differences of 0.183 nucleotide substitutions per position. The distance between species varied from 0.139 ± 0.014 in the S. markewitschi–S. carpionis pair to 0.179 ± 0.015 in the S. stellata–S. californiensis pair. The intraspecific nucleotide diversity of the COI gene fragment is much lower: for S. californiensis and S. edwardsii, inhabiting the gill cavity and fins of the host – 0.013 ± 0.003 and 0.015 ± 0.003, and for S. stellata, S. markewitschi, and S. carpionis, localized in the buccal cavity of the hosts – 0.002 ± 0.001, 0.004 ± 0.001, and 0.005 ± 0.001, respectively. A comparison of samples of three Salmincola copepod species from different regions of the Russian Far East revealed a significant (Fst = 0.28–0.42, P \( \ll \) 0.001) genetic subdivision. Three subclades of edwardsii-like copepods – S. edwardsii from the Russian Far East, S. edwardsii from the American brook char of eastern North America, and S. siscowet from the lake char of Michigan (COI sequences of copepods from the last two groups are taken from genetic databases) – differed from each other by an average of 9.3–10.9% nucleotide positions, which means the need for a taxonomic revision of S. edwardsii. According to the molecular dating carried out, the divergence of Salmincola lineages started in the Miocene and ended in the early Pliocene. The phylogenetic substitution rate was 0.0228 (95% interval: 0.0132–0.033) nucleotide substitutions/position/million years/lineage. The rate of nucleotide substitutions at the population level is 3.7 times higher – 0.0849 (0.0212–0.170). The high level of variability of the COI gene fragment makes this marker a useful tool both for developing the taxonomy and phylogeny of Salmincola and Lernaeopodidae copepods at the species and genus levels, and for analyzing the differentiation of their populations.

DHA and EPA levels in a piscivorous fish changed by preying upon stocked salmon fry

Increases in prey population size can affect the physiology and ecology of upper-trophic level organisms. This phenomenon is known as a bottom-up effect. For example, the increased abundance of prey resources can trigger physiological (internal) changes in predators, such as improvements in nutritional status. However, these physiological aspects of bottom-up effects have not been considered. In this study, we tested the hypothesis that white-spotted charr Salvelinus leucomaenis, a salmonid fish, increases body stores of omega-3 fatty acids, especially docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), by preying upon stocked hatchery-reared masu salmon Oncorhynchus masou fry in streams. The dynamics of fatty acid contents in charr inhabiting salmon-stocked and unstocked streams clearly support this hypothesis: fatty acid contents (DHA, EPA, and total fatty acid) increased after stocking in stocked streams, but not in unstocked streams. In addition, DHA increased with increasing body size of white-spotted charr and vice versa for EPA. The impacts of human activities, such as fish stocking, on freshwater ecosystems are a matter of serious concern for conservation. Future attempts to gain a comprehensive understanding of the impacts of fish stocking should consider not only community ecology but also physiology.

CRISPR/Cas9-mediated knock-in of masu salmon (Oncorhyncus masou) elongase gene in the melanocortin-4 (mc4r) coding region of channel catfish (Ictalurus punctatus) genome.

Channel catfish, Ictalurus punctatus, have limited ability to synthesize Ω-3 fatty acids. The ccβA-msElovl2 transgene containing masu salmon, Oncorhynchus masou, elongase gene driven by the common carp, Cyprinus carpio, β-actin promoter was inserted into the channel catfish melanocortin-4 receptor (mc4r) gene site using the two-hit two-oligo with plasmid (2H2OP) method. The best performing sgRNA resulted in a knockout mutation rate of 92%, a knock-in rate of 54% and a simultaneous knockout/knock-in rate of 49%. Fish containing both the ccβA-msElovl2 transgene knock-in and mc4r knockout (Elovl2) were 41.8% larger than controls at 6months post-hatch (p = 0.005). Mean eicosapentaenoic acid (EPA, C20:5n-3) levels in Elov2 mutants and mc4r knockout mutants (MC4R) were 121.6% and 94.1% higher than in controls, respectively (p = 0.045; p = 0.025). Observed mean docosahexaenoic acid (DHA, C22:6n-3) and total EPA + DHA content was 32.8% and 45.1% higher, respectively, in Elovl2 transgenic channel catfish than controls (p = 0.368; p = 0.025). To our knowledge this is the first example of genome engineering to simultaneously target transgenesis and knock-out a gene in a commercially important aquaculture species for multiple improved performance traits. With a high transgene integration rate, improved growth, and higher omega-3 fatty acid content, the use of Elovl2 transgenic channel catfish appears beneficial for application on commercial farms.

Metabolic changes in juvenile masu salmon during starvation and after release into the Iburibashi River in the Hokuriku region: An attempt to evaluate the nutritional condition of released fish using biochemical indices

Metabolic changes in juvenile masu salmon during starvation and after release into the Iburibashi River in the Hokuriku region: An attempt to evaluate the nutritional condition of released fish using biochemical indices

Evaluation of binding capacity of circulating insulin-like growth factor binding protein-1b in salmonids using a ligand immunofunctional assay

Insulin-like growth factor-binding proteins (IGFBPs) regulate the activity of insulin-like growth factor (IGF)-1. Among the three major circulating IGFBPs in salmonids, IGFBP-1b is an inhibitor of IGF activity induced under catabolic conditions. IGFBP-1b is considered to quickly sequester IGF-1 from the circulation. However, the level of circulating IGFBP-1b present in its unoccupied free form is unknown. Here, we aimed to develop a non-equilibrium ligand immunofunctional assay (LIFA) to evaluate IGF-binding capacity of circulating intact IGFBP-1b. Purified Chinook salmon IGFBP-1b, its antiserum, and europium-labeled salmon IGF-1 were used as the assay components. In the LIFA, IGFBP-1b was first captured by the antiserum, allowed to bind to the labeled IGF-1 for 22 h at 4 °C, and quantified its IGF-binding capacity. Serial dilutions of the standard and serum were prepared simultaneously within a certain concentration range (1.1–12.5 ng/ml). In underyearling masu salmon, IGF-binding capacity of intact IGFBP-1b was higher in fasted fish than in fed fish. Transferring Chinook salmon parr to seawater also increased IGF-binding capacity of IGFBP-1b, most likely due to osmotic stress. In addition, there was a strong relationship between total IGFBP-1b levels and its IGF-binding capacity. These results suggest that IGFBP-1b expressed under stress is mostly present in the free form. On the contrary, during smoltification of masu salmon, IGF-binding capacity of IGFBP-1b in the serum was relatively low and less related to the total IGFBP-1b level, suggesting its functional difference under certain physiological conditions. These results indicate that estimating both total IGFBP-1b level and its IGF-binding capacity is useful for evaluating the catabolic status and unraveling the regulation of IGF-1 activity by IGFBP-1b.

Changes in length of period of the spawning run for pacific salmons in the rivers in the north of Primorsky Territory

Comparative data on changes in structure and length of the spawning run for chum salmon, cherry salmon and pink salmon in the rivers of the northern part of Primorsky Territory are presented for 1998–2022. Appearance of new seasonal groups is noted for all these species. Length of the periods of spawning has become longer.

Научно-производственная компания «АКВАТЕХ» новый лидер в производстве стартовых кормов для молоди тихоокеанских лососей

We analyzed the feeding efficiency of pink salmon (Oncorhynchus gorbuscha), chum salmon (O. keta), masu salmon (O. masu) and coho salmon (O. kisutch) juveniles at the federal fish hatcheries of Sakhalin during seven fish breeding cycles using starter feeds from «Aller Aqua» (Denmark) and «Aquatech» (Russia). It was established that the feed coefficient when using Russian-made feed was lower at all enterprises and when growing juveniles of each salmon species. In addition to the quality of the feed itself, this may be due to the combined effect of two factors, firstly, with the use of special feeds with biologically active additives to stimulate immunity at the initial stages of feeding, and secondly, with the presentation of feeds in two flotation options «conditionally floating» or slowly sinking and «floating» or floating, as well as the selection by experience for each enterprise of the most suitable option.

Effects of domestication and captive breeding on reaction to moving objects: implications for avoidance behaviours of masu salmon Oncorhynchus masou

Domestication and captive breeding can compromise the obstacle- and predator-avoidance capabilities of animals in the wild. Whereas previous studies only examined these effects in combination, here we examine them individually by comparing the abilities of wild, F1 (offspring of wild parents) and captive-bred (approx. F15) masu salmon Oncorhynchus masou to avoid a falling object under experimental conditions. Rates of avoidance failure were low (wild, 12.5%; F1, 10.7%; captive-bred, 8%) under light conditions, but increased under dark conditions (wild, 11.1%; F1, 32.1%; captive-bred, 60.0%). We attribute the elevated avoidance failure rate among F1 fish to the lack of learning opportunities in hatchery environments (i.e. domestication), and the further elevation of avoidance failure rate among captive-bred fish to the degradation of sensory organ function (i.e. captive breeding). These results imply reduced survival rates for F1 and captive-bred fish in the wild and are consistent with the low stocking efficiencies reported for captive-bred masu salmon.

Seasonal ecosystem linkages contribute to the maintenance of migratory polymorphism in a salmonid population.

The influence of resource subsidies on animal growth, survival and reproduction is well understood, but their ultimate effects on life history have been less explored. Some wild species have a partially migratory life history, wherein migration is dictated based upon threshold traits regulated in part by the seasonal availability of resources. We conducted a large-scale field manipulation experiment where we provided a terrestrial invertebrate subsidy to red-spotted masu salmon. Individuals in stream reaches that received a subsidy had, on average, a 53% increase in growth rate relative to those in control reaches. This increased growth resulted in a greater proportion of individuals reaching the threshold body size and smolting in the autumn. Consequently, 19-55% of females in subsidized reaches became migratory, whereas 0-14% became migratory in the control reaches. Our findings highlight seasonal ecosystem linkage as a key ecosystem property for maintaining migratory polymorphism in partially migratory animals.

To the issue of the origin of false annual rings on scale of juvenile Pacifi c salmon in the Bolshaya River system (Southeast Kamchatka)

Seasonal growth and formation of annual rings on scale of juvenile Pacifi c salmon (Chinook, sockeye, coho and cherry salmons) restart in the Bolshaya River basin from mid May to mid June. In the last half of June and until the end of July, there are actually no additional formations on the scales of both underyearlings and yearlings. In August–October false annual rings (FARs) of dense circuli can be observed on scales of underyearlings of species mentioned above. Forming the extra FARs in the yearlings of coho and cherry salmon during their second season of growth not found (few exceptions only). The underyearling’s FARs are most frequent (17.4%) in Chinook salmon, following by sockeye salmon (12.1%) and coho salmon (7.1%), and the most rare (1.0%) in cherry salmon. The frequency of the FARs in yearlings during their growth period in the fi rst summer is 28.1% in Chinook salmon, 12.6% in sockeye salmon, 11.7% in coho salmon and 4.8% in cherry salmon.

Assessment of stock abundance and commercial perspective for cherry salmon (Oncorhynchus masou) in the water bodies of West Kamchatka

The paper presents generalized information for the ten-year period (2011–2020) on the stock abundance status of some West Kamchatka cherry salmon populations. Data on spawning stock abundance and catch statistics from scientifi c and recreational fi sheries are given. The sex and age structure is considered. Dynamics of body length and weight and absolute fecundity are analyzed. The results of the study make it possible to consider the West Kamchatka cherry salmon as a recreational fi shery object for the nearest decade.

Recent reduction of genetic diversity in markless form of the red-spotted masu salmon Oncorhynchus masou ishikawae in the Ono River, Kyushu, Japan

Recent reduction of genetic diversity in markless form of the red-spotted masu salmon Oncorhynchus masou ishikawae in the Ono River, Kyushu, Japan

Molecular mechanisms of the virulence and efficacy of a highly virulent Vibrio anguillarum strain and its formalin-inactivated vaccine in rainbow trout.

In this study, we have isolated four strains of Vibrio anguillarum, revealing that they share the same serotype of O1, biochemical characteristics and virulence factor genes. However, there were differences in haemolytic activity among the bacterial strains; a strain with lower pathogenicity showed γ-haemolytic activity, whereas other virulent strains showed α-haemolytic activity on blood agar and higher empA gene expression in RTG-2 cell line. The most virulent strain was V. anguillarum RTBHR from diseased masu salmon (Oncorhynchus masou), which resulted in mortality of 100% and 93.3% when injected intraperitoneally at concentrations of 9 × 105 and 6.3 × 105 colony-forming units/fish in rainbow trout (Oncorhynchus mykiss) and Coho salmon (Oncorhynchus kisutch), respectively. A formalin-inactivated vaccine of V. anguillarum RTBHR induced a protective and specific immunity in rainbow trout as the vaccinated fish exhibited low cumulative mortality in a challenge test and a high specific antibody response in enzyme-linked immunosorbent assay at 8 weeks post-vaccination. The produced antibody was bound to bacterial proteins of 30-37 kDa in size. This adaptive immune response was detected as early as day 1, with quantitative polymerase chain reaction analysis revealing the upregulated expression of genes encoding for TCRα, T-bet, mIgM and sIgM in rainbow trout. This suggested that the vaccine inducedT (probably a more dominant Th1 response) and B cell responses. In conclusion, the vaccine successfully protected fish from V. anguillarum infection by eliciting cellular and humoral immune responses.

Overlap in spawning habitat characteristics between two salmonids in relation to stream size: redd superimposition hypothesis on longitudinal species replacement

Redd superimposition, spawning on a previous spawner's redd by a later spawner, reduces reproductive success of the previous spawner. Therefore, in streams where redd superimposition frequently occurs, late-spawning species have a competitive advantage over early-spawning species. We hypothesised that smaller channels of upper reaches would have higher potential of redd superimposition owing to lower availability of spawning habitat, thereby providing a competitive advantage to late-spawning species, to explain a displacement of native masu salmon ( Oncorhynchus masou ishikawae) by non-native white-spotted char ( Salvelinus leucomaenis) (late spawner) specific to small upper reaches in a Japanese river. We examined (1) the availability of spawning habitat and (2) overlap in spawning habitat characteristics between the two species in streams with different channel size. The results showed that (1) the habitat availability decreased upstream as channel size decreased, and (2) characteristics of spawning habitat highly overlapped between the two species in small channels, whereas those differed significantly between the two species in larger channels, supporting our hypothesis. Our results provide a new perspective on longitudinal changes in competitive advantages in salmonids.

Ecosystem Functions of a Spring-Fed Tributary in Providing Foraging Habitat and Thermal Refuge for Juvenile Masu Salmon

<i>Ichthyology & Herpetology</i> (formerly <i>Copeia</i>) publishes work on the biology of fishes, amphibians, and reptiles, or work using those organisms as models for testing hypotheses of broad significance.

Changes in smolt timing and age at maturity caused by crossbreeding wild- and hatchery-reared masu salmon

種苗放流されるヤマメ養殖魚との交雑が野生サクラマスの生活史形質に及ぼす影響を評価するため，米代川産サクラマスの雌と関東地方由来のヤマメ養殖魚の雄を交雑させた。作出した交雑魚のスモルト化の盛期は3月であり，養殖ヤマメ（12月）と米代川産サクラマス（4月）の中間であった。1歳における交雑魚の雌の成熟率は43.1%であり，ヤマメ養殖魚（75.7%）と米代川産サクラマス（6.8%）の中間であった。得られた結果から，ヤマメ養殖魚との交雑によってサクラマス地域個体群の生活史特性が変化する可能性が示唆された。

Interactions between fish and angler behaviour affect species-specific catchability of sympatric native charr and two introduced trout

Catchability is a key determinant of fishing pressure, and plays an important role in the management of recreational fisheries. We investigated the catchability of three sympatric salmonid species in a recreational fishery in Lake Shikaribetsu, Japan—the endemic Miyabe charr (Salvelinus malma miyabei), introduced masu salmon (Oncorhynchus masou), and introduced rainbow trout (O. mykiss)—using a combination of stock assessment and angler survey data. Catchability differed among species, angling gear, and the interaction between these two, even when a similar fishing gear was used. Because of its migratory behaviour and fishing gear restrictions, the catchability of Miyabe charr was the lowest of these species, which became lower as fish density was lower. Conversely, the density-dependent changes of the catchability were not detected in masu salmon which few anglers targeted specifically. Rainbow trout catchability by fly anglers was the highest, possibly because the fishing tactics of fly anglers targeting this species were tailored to its foraging behaviour. We regarded differences in catchability among these three salmonids to be related to differences in fish and angler behaviours. These results indicate that behavioural characteristics of both fish species and anglers can cause different fishing pressure in a single recreational fishery targeting multispecies fish via interspecific catchability, and they should be taken into account for their management.