Evolutionary-physiological aspects of adaptation of the Pacific salmon fry of the oncorhynchus genus to migration to the sea water

A complex of adaptive changes occurring in the Pacific salmon fry in the process of migration to the sea is described, including behavior, ion content in carcasses, and morphological changes in Stannius bodies, gill epithelium, and nephron tubular epithelium. Participating in experiments with transfer from fresh water into a two-layer aquarium (the lower layer—sea water, the upper layer—fresh water) were smolts of chum salmon and underyearlings of cherry salmon as well as the trachurus and leiurus forms of the three-spined stickleback Casterosteus aculeatus. All fish, regardless of their salt preference, at once after placement into the two-layer aquarium, occupied the sea water zone, at the very bottom of the aquarium. After 1 h, there started brief excursions of cherry salmon and chum salmon to the upper, fresh water layer; however, both forms of the three-spined stickleback did not participate in these excursions. After 12 h, the chum salmon settled down in the lower, sea water layer, while the cherry salmon—in the upper, fresh water layer. Both forms of the three-spined stickleback never left the sea water layer and felt quite comfortably on the aquarium bottom. It seems that the high tolerance of the both stickleback forms to wide salinity limits allows them to choose the convenient position regardless of the water salt composition. By analyzing the material obtained for three years (2001–2003) on structure and functions of the gill epithelium chloride cells (CC), we have come to the conclusion that the fresh water fry of two salmon species, chum and cherry salmons, caught at the same time and practically in the same water reservoirs can be divided into three groups. The underyearlings of the cherry salmon as a rule are characterized by the thickened epithelium of secondary gill lamellae, but by a very small number of CC. In smolts of chum salmon, on the contrary, the epithelium is sufficiently thin, but enriched in the CC that demonstrate an active structure in the very beginning of migration to sea. However, with approaching the sea (and with an increase of terms of migration) the CC activity drops, but their amount does not change. And only after migration to the sea the CC activity rises again, although their amount seems to remain unchanged. The described peculiarities of behavior and of the ion composition regulation in the migrating salmon fry confirm the hypothesis that the salmons evolutionized in fresh water, that the Oncorhynchus genus appeared in large spaces of saltish waters, such as the Japan sea at the period of the early Pleistocene, and that learning of fry of the Oncorhynchus genus (for instance, of O. gorbuscha and O. keta) is the most specialized in the salmons migration to the sea, whereas the fresh water species of chars (Salvelinus) and of trouts (Salmo) are more primitive.     

Evidence of potential establishment of pink salmon Oncorhynchus gorbuscha in Scotland

In spring 2022, pink salmon Oncorhynchus gorbuscha smolts were recorded in the UK. Fish were caught in the Rivers Thurso and Oykel in Scotland between 13 and 17 March. To the authors’ knowledge, this is the first observation of O. gorbuscha smolts in Europe outside the Scandinavian and Kola peninsulas, including other tributaries of the White and Barents Seas. It also provides evidence of successful spawning in 2021 and completion of the freshwater phase of the life cycle, and indicates the possibility for potential establishment of an O. gorbuscha population in Great Britain.     

Evidence of successful recruitment of non-native pink salmon Oncorhynchus gorbuscha in Iceland

In mid-May 2022, pink salmon Oncorhynchus gorbuscha smolts were caught in the rivers Botnsá, Grímsá, and Langá in Iceland. This observation provides the first evidence of successful spawning and the completion of the freshwater phase of the life cycle in Icelandic rivers. It is the most western record of O. gorbuscha smolts in Europe, further west than Russia, Norway, and the UK. Smolts originating from Iceland potentially support the recruitment of this species in the North Atlantic and may lead to the establishment of a self-sustaining population in Iceland.     

On Catching Humpback Salmon Oncorhynchus gorbuscha and Chum Salmon Oncorhynchus keta of Rare Age

Data on catching humpback salmon Oncorhynchus gorbuscha at the age of 0+ and chum salmon Oncorhynchus keta at the age of 1+ in the Ilyushina River (Kunashir Island) in the period of spawning migration are given. The sex of fish, the body length, the stage of gonad maturity, and the number and width of sclerites on scales are indicated.     

Evolutionary-physiological aspects of adaptation of the Pacific salmon fry of the Oncorhynchus genus to migration to the sea water

A complex of adaptive changes occurring in the Pacific salmon fry in the process of migration to the sea is described, including behavior, ion content in carcasses, and morphological changes in Stannius bodies, gill epithelium, and nephron tubular epithelium. Participating in experiments with transfer from fresh water into a two-layer aquarium (the lower layer - sea water, the upper layer - fresh water) were smolts of chum salmon and underyearlings of masu salmon as well as the trachurus and leiurus forms of the three-spined stickleback Casterosteus aculeatus. All fish, regardless of their salt preference, at once after placement into the two-layer aquarium, occupied the sea water zone, at the very bottom of the aquarium. After 1 h, there started brief excursions of masu salmon and chum salmon to the upper, fresh water layer; however, both forms of the three-spined stickleback did not participate in these excursions. After 12 h, the chum salmon settled down in the lower, sea water layer, while the masu salmon - in the upper, fresh water layer. Both forms of the three-spined stickleback never left the sea water layer and felt quite comfortably on the aquarium bottom. It seems that the high tolerance of the both stickleback forms to wide salinity limits allows them to choose the convenient position regardless of the water salt composition. By analyzing the material obtained for three years (2001-2003) on structure and functions of the gill epithelium chloride cells (CC), we have come to the conclusion that the fresh water fry of two salmon species, chum and masu salmons, caught at the same time and practically in the same water reservoirs can be divided into three groups. The underyearlings of the masu salmon as a rule are characterized by the thickened epithelium of secondary gill lamellae, but by a very small number of CC. In smolts of chum salmon, on the contrary, the epithelium is sufficiently thin, but enriched in the CC that demonstrate an active structure in the very beginning of migration to sea. However, with approaching the sea (and with an increase of terms of migration) the CC activity drops, but their amount does not change. And only after migration to the sea the CC activity rises again, although their amount seems to remain unchanged. The described peculiarities of behavior and of the ion composition regulation in the migrating salmon fry confirm the hypothesis that the salmons evolutionized in fresh water, that the Oncorhynchus genus appeared in large spaces of saltish waters, such as the Japan Sea at the period of the early Pleistocene, and that learning of fry of the Oncorhynchus genus (for instance, of O. gorbuscha and O. keta) is the most specialized in the salmons migrating to the sea, whereas the fresh water species of chars (Salvelinus) and of trouts (Salmo) are more primitive.     

Comparative Study of Substrate–Inhibitor Specificity of Brain Cholinesterase Activity of Pacific Salmon Fish of the Salmonidae Family

Salmon fish of the Salmonidae family, representatives of the Pacific salmon Oncorhynchus genus, the humpback salmon O. gorbuscha Wielb., dog salmon O. keta, coho salmon O. kisutch, blueback salmon O. nerka, and chinook salmon O. tschawytscha, and also of noble salmons genus, Salmo—black salmon S. salar, caught in the northwest water area of the Pacific ocean, are studied in the work. Iodides of acetyl-, propionyl-, and butyrylthiocholine were used as substrates. Carbamate proserine and 5 organophosphorus inhibitors were studied as inhibitors. Testing of homogeneity of cholinesterase activity in the brain tissue has revealed only one enzyme in the coho salmon, while several enzymes, in the dog salmon and humpback salmon, which can be an enzymologic argument for the favor of hypothesis about the presence of interspecies groups among Pacific salmons of the Oncorhynchus genus. Interspecies differences in substrate specificity of the brain tissue in the studied salmonid species are found. The fish enzymes of the fishes have shown a high sensitivity to proserine. Only in the case of diisopropylfluorophosphate, both interspecies and intergenus differences are revealed.     

Net ground speed of downstream migrating radio-tagged Atlantic salmon (Salmo salar L.) and brown trout (Salmo trutta L.) smolts in relation to environmental factors

The downstream migration of Atlantic salmon (Salmo salarL.) and sea trout smolt (S. trutta L.) was investigated using radio telemetry in the spring of 1999 and 2000. Forty wild sea trout smolts, 20 F1 sea trout smolts, 20 hatchery salmon smolts and 20 salmon smolts from river stockings were radio tagged and released in the Danish River Lilleaa. The downstream migration of the different groups of fish was monitored by manual tracking and by three automatic listening stations. The downstream migration of radio tagged smolts of both species occurred concurrently with their untagged counterparts. The diel migration pattern of the radio tagged smolts was predominantly nocturnal in both species. Wild sea trout smolt migrated significantly faster than both the F1 trout and the introduced salmon. There was no correlation between net ground speed, gill Na⁺,K⁺-ATPase activity or fish length in any of the different groups. The migration speed of wild sea trout smolts was positively correlated with water discharge in both years. In F1 sea trout smolts, migration speed was positively correlated with temperature in 1999. The migration speed of salmon smolts did not correlate to any of the investigated parameters.     

Active feeding of downstream migrating juvenile pink salmon (Oncorhynchus gorbuscha) revealed in a large Barents Sea river using diet and stable isotope analysis

The recent, rapid spreading of non-native pink salmon Oncorhynchus gorbuscha in the North Atlantic area has raised concerns about their possible negative impacts on native salmonid species. Potential interactions include competition for food resources during the short freshwater phase of juvenile O. gorbuscha, but little is known about their feeding behavior in the newly occupied North Atlantic rivers. Using stable isotope and stomach content analyses, patterns of freshwater feeding of non-native O. gorbuscha fry were studied in a large Fennoscandian river, the Teno, that discharges to the Barents Sea. Changes in stable isotope values (δ¹³C, δ¹⁵N, δ³⁴S) and stomach contents from the period of emergence (April to mid-May) to estuarine entry (late May/June) were examined and provided both temporally integrated and short-term indicators of freshwater feeding dependency. In addition, the occurrence of juvenile O. gorbuscha and changes in their length and weight during their emergence/migration period were investigated. Juvenile O. gorbuscha were at the spawning grounds from April through to mid-May with abundance peaking in mid-May. Fish moved to the estuary by late May and their abundance decreased toward June, and their body size increased concurrently. Stomach analyses indicated no feeding activity in April–early May in the spawning areas, but the stomach fullness indices increased markedly in fish sampled in the estuary in May and June. The most important prey items in stomachs were Chironomidae and Ephemeroptera larvae. Significant changes in all analysed stable isotopes were detected among sample periods, with a peak in mid-May and June showing significantly lower values than other sample periods. A change from the higher values reflective of parental marine feeding to the lower values reflective of freshwater feeding indicated active in-river feeding by juveniles during the study period. The documented active freshwater feeding of non-native juvenile O. gorbuscha suggests potential resource competition with native fluvial fishes, particularly salmonids.     

Olfactory gene expression in migrating adult sockeye salmon Oncorhynchus nerka

Expression of 12 olfactory genes was analysed in adult sockeye salmon Oncorhynchus nerka nearing spawning grounds and O. nerka that had strayed from their natal migration route. Variation was found in six of these genes, all of which were olfc olfactory receptors and had lower expression levels in salmon nearing spawning grounds. The results may reflect decreased sensitivity to natal water olfactory cues as these fish are no longer seeking the correct migratory route. The expression of olfactory genes during the olfactory‐mediated spawning migration of Pacific salmon Oncorhynchus spp. is largely unexplored and these findings demonstrate a link between migratory behaviours and olfactory plasticity that provides a basis for future molecular research on salmon homing.     

Das skelett des buckellachses (Oncorhynchus gorbuscha walb.)

Zusammenfassung Anhand von Röntgenaufnahmen wurde die Frage geprüft, welche Veränderungen am Skelett beim männlichen Buckellachs bei der Ausbildung des Buckels ablaufen.Die Wirbelsäule bleibt unverändert. Die dorsalen Dornfortsätze, Neuralia, und die Fleischgräten in der Buckelgegend, Epineuralia und Interneuralia, verlängern und verdicken sich sehr stark. Sie bilden die knöcherne Stütze Mr den Buckel.Eine Rückbildung des Buckels findet nicht statt, da die Tiere nach der Laichzeit zugrunde gehen.

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Summary Using radiograms of male specimens of the humpback salmon (Oncorhynchus gorbuscha) the following question is discussed: Which variation of the skeleton takes place during the development of the humpback?The vertebrate column is not changed. The dorsal processus spinales (Neuralia) and the fish-bones in the region of the humpback (Epineuralia and Interneuralia) are very much elongated and thicked. They are the bony support of the humpback. A restitution of the normal state takes not place because the animals die immediately after the spawning time.

     

Straying of hatchery salmon in Prince William Sound,Alaska

The straying of hatchery salmon may harm wild salmon populations through a variety of ecological and genetic mechanisms. Surveys of pink (Oncorhynchus gorbuscha), chum (O. keta) and sockeye (O. nerka) salmon in wild salmon spawning locations in Prince William Sound (PWS), Alaska since 1997 show a wide range of hatchery straying. The analysis of thermally marked otoliths collected from carcasses indicate that 0–98% of pink salmon, 0–63% of chum salmon and 0–93% of sockeye salmon in spawning areas are hatchery fish, producing an unknown number of hatchery-wild hybrids. Most spawning locations sampled (77%) had hatchery pink salmon from three or more hatcheries, and 51% had annual escapements consisting of more than 10% hatchery pink salmon during at least one of the years surveyed. An exponential decay model of the percentage of hatchery pink salmon strays with distance from hatcheries indicated that streams throughout PWS contain more than 10% hatchery pink salmon. The prevalence of hatchery pink salmon strays in streams increased throughout the spawning season, while the prevalence of hatchery chum salmon decreased. The level of hatchery salmon strays in many areas of PWS are beyond all proposed thresholds (2–10%), which confounds wild salmon escapement goals and may harm the productivity, genetic diversity and fitness of wild salmon in this region     

Daily feeding rhythm and rations of Pacific salmon of the genus Oncorhynchus in the period of marine prespawning migrations

The daily feeding rhythm and rations of the humpback salmon Oncorhynchus gorbuscha, the sockeyed salmon O. nerka, and the chum salmon O. keta during marine prespawning migrations is investigated with consideration of materials collected at daily stations in waters off eastern Kamchatka in June–July 1999 and 2001 (from catches of drift nets). The bulk of humpback salmon and sockeyed salmon food consists of euphausiids, hyperiids, large copepods, pteropods, and fish juveniles. In the food of chum salmon, pteropods dominated. In a 24-h period, salmon manifest a pronounced evening peak of stomach fullness, while at night feeding discontinues. Samples collected in the morning consisted of fish who had just started feeding after the night pause. In addition to nightly period of rest, all species manifested a daytime decrease in foraging activity, though less pronounced than in the night. The daily rhythm of Pacific salmons’s feeding depends on the vertical migrations of their food items (representatives of sound-scattering layers). During the marine feeding period, the most intensive feeding is recorded in the humpback salmon and chum salmon. The daily ration of the humpback salmon is lower than that of the chum salmon but includes animals of higher food value. Due to a high digestion rate in combination with a large stomach volume, the chum salmon can consume a large quantity of low-calorific food in a short time. The daily ration of the sockeyed salmon is considerably lower than that of other salmon species.     

Widespread occurrence of pink salmon (Oncorhynchus gorbuscha) throughout Greenland coastal waters

Using social media, the Greenland Institute of Natural Resources collected data on the occurrence of pink salmon (Oncorhynchus gorbuscha) in 2019. Eighty-four pink salmon were reported from 22 locations across Greenland. This comprised 76 specimens from 2019 and 8 specimens from 2013 to 2018. Of these, 12 were caught in fresh water, and a single pink salmon was from the bottom of the Nuuk Fjord near the Kapisillit River – the only known river in Greenland where the Atlantic salmon (Salmo salar) spawn. It is unknown if pink salmon have reproduced in Greenland waters.     

Characteristics of the spawning stock of chinook salmon <Emphasis Type="Italic">Oncorhynchus tshawytscha</Emphasis> from the Apuka River (northeastern Kamchatka)

Biological features of chinook salmon Oncorhynchus tshawytscha from the Apuka River, the largest river of the northeastern Kamchatka inflowing Olyutorskii Bay of the Bering Sea, are studied. Chinook salmon from the Apuka River spend mainly a year in the river before downstream migration to the sea. The fish live in the sea for 1–4 years. The spawning migration of chinook salmon into the Apuka River begins in late May just after ice melting, and it continues until early August. The main part of the spawners enters the river during June. A hypothesis on the occurrence of two seasonal races in the Apuka River is proposed.     

Climate warming causes phenological shift in Pink Salmon, Oncorhynchus gorbuscha, behavior at Auke Creek, Alaska

Thirty‐four years (1972–2005) of water temperature data and extensive biological observations at Auke Creek, Alaska indicate a general warming trend that affected the native pink salmon (Oncorhynchus gorbuscha) population. Serial environmental records at nearby Auke Bay, Alaska over 46 years show trends of increasing air and sea surface temperatures. Trends of increased total precipitation and earlier date of ice out on nearby Auke Lake also occurred, but not at significant rates. Average water temperatures during the incubation of pink salmon in Auke Creek increased at a rate of 0.03 °C yr^?1 over the 34‐year period. For the 1972–2005 broods, midpoints of fry migrations from Auke Creek ranged between April 2 and May 7, and there was a trend of earlier migration of pink salmon fry at a rate of ? 0.5 days yr^?1. The migration timing of adult salmon into Auke Creek also showed a trend toward earlier timing. The earlier adult migration combined with warmer incubation temperatures are related to earlier migration of pink salmon fry. If the observed warming trend continues, Auke Creek may become unsuitable habitat for pink salmon. Given the trend for salmon fry to migrate earlier, a larger portion of the population may become mismatched with optimum environmental conditions during their early marine life history. If salmon adults continue to migrate into the creek earlier when water temperatures are commonly high, it will result in increased prespawning mortality.     

Environmental correlates of life-history variation in juvenile chinook salmon, Oncorhynchus tshawytscha (Walbaum)

Throughout its native North Pacific, the chinook salmon, Oncorhynchus tshawytscha (Walbaum), exists as twolife-history types that aredistinguished by the age at which juvenile salmon migrate to sea as smolts. 'Stream-type' chinook migrate seaward after I or more years of feeding in fresh water, whereas 'ocean-type' fish migrate to sea as newly emerged fry or after 2–3 months in fresh water. Stream-type chinook predominate in populations distant from the sea south of 56° N, and in both inland and coastal populations north of this point. By contrast, ocean-type chinook predominate in coastal populations south of 56° N, but are rare in populations in more northerly latitudes. Stream-type populations are associated with areas of low 'growth opportunity' (as measured by temperature and photoperiod regimes) and/or areas distant from the sea compared to ocean-type. Geographic variability in juvenile life history is suggested to result, in part, from environmental modulation of smolting timing via differences in growth opportunity among geo-graphic areas. In addition, differences in migration distance and temperature regime may result in selection for different sizes at migration among populations which, through differences in growth opportunity, might promote geographic variability in age at seaward migration.     

Experimental and natural host specificity of Loma salmonae (Microsporidia)

The microsporidian Loma salmonae (Putz, Hoffman & Dunbar, 1965) Morrison & Sprague, 1981 has caused significant gill disease in Pacific salmon Oncorhynchus spp. Host specificity of the parasite was examined experimentally by per os challenge of selected salmonids and non-salmonids with infective chinook salmon O. tshawytscha gill material. Pink Oncorhynchus gorbuscha and chum salmon O. keta, brown Salmo trutta and brook trout Salvelinus fontinalis, and chinook salmon (controls) were positive, whereas Atlantic salmon Salmo salar and Arctic char Salvelinus alpinus were negative. In addition, no non-salmonids were susceptible to experimental exposure. Wild Pacific salmon species in British Columbia, Canada, were examined for L. salmonae during their freshwater life history stages (smolts, prespawning, spawning). All stages were infected, although infections in smolts were only detectable using a L. salmonae-specific PCR test. Many previous Loma spp. described from Oncorhychus spp. are likely L. salmonae based on host, parasite morphology, and site of infection.     

Life-history styles and somatic allocation in iteroporous arctic charr and semelparous pink salmon

Synopsis RNA/DNA ratios were used to estimate recent somatic allocation of spawning arctic charr,Salvelinus alpinus, and pink salmon,Oncorhynchus gorbuscha. Smaller arctic charr morphs had lower ratios than larger morphs. Larger male pink salmon had lower ratios than smaller males. Thus recent somatic allocation (anabolic metabolic activity and growth) is coupled with cumulative lifetime growth in iteroparous arctic charr, but is uncoupled in semelparous pink salmon. These data suggest that somatic investment in these species is being differentially effected by the energetic costs of reproduction.     

Environmental requirements of common riverine European salmonid fish species in fresh water with particular reference to physical and chemical aspects

This review attempts to assess, as quantitatively as possible, the habitat requirements in fresh water of three common and widespread European salmonid species. Namely: the trout (Salmo trutta L.), the salmon (S. salar L.) and the grayling (Thymallus thymallus L.). Requirements are considered for spawning, incubation and emergence, juveniles and smolts and for adults and spawning movements.     

Early life stage salinity tolerance of wild and hatchery-reared juvenile pink salmon Oncorhynchus gorbuscha

Salinity tolerance in wild (Glendale) and hatchery (Quinsam) pink salmon Oncorhynchus gorbuscha (average mass 0·2 g) was assessed by measuring whole body [Na⁺] and [Cl^?] after 24 or 72 h exposures to fresh water (FW) and 33, 66 or 100% sea water (SW). Gill Na⁺, K⁺‐ATPase activity was measured following exposure to FW and 100% SW and increased significantly in both populations after a 24 h exposure to 100% SW. Whole body [Na⁺] and whole body [Cl^?] increased significantly in both populations after 24 h in 33, 66 and 100% SW, where whole body [Cl^?] differed significantly between Quinsam and Glendale populations. Extending the seawater exposure to 72 h resulted in no further increases in whole body [Na⁺] and whole body [Cl^?] at any salinity, but there was more variability among the responses of the two populations. Per cent whole body water (c. 81%) was maintained in all groups of fish regardless of salinity exposure or population, indicating that the increase in whole body ion levels may have been related to maintaining water balance as no mortality was observed in this study. Thus, both wild and hatchery juvenile O. gorbuscha tolerated abrupt salinity changes, which triggered an increase in gill Na⁺, K⁺‐ATPase within 24 h. These results are discussed in terms of the preparedness of emerging O. gorbuscha for the marine phase of their life cycle.