The relationships between fish health, metabolic rate, swimming performance and recovery in return-run sockeye salmon, Oncorhynchus nerka (Walbaum)

The repeat swimming ability and oxygen uptake (Mo2) of adult sockeye salmon, Oncorhynchus nerka (Walbaum), were assessed at ambient water temperatures at three field locations along their migration route. Following these measurements, internal and external fish condition was evaluated according to United States Environmental Protection Agency guidelines. Here we report on the physiological characteristics of fish having either moderate or severe levels of disease and injury. Routine oxygen uptake (Mo2) did not differ between healthy fish and those with indices of ill health. In contrast, fish classified as sick, which included conditions of damaged internal organs, an Ichthyophonus spp. heart infection, a Saprolegnia spp. gill infection, and skin wounds, had a lower post-exercise Mo2 and were unable to repeat their critical swim speed (U(crit)) on the second swim test. Moderate levels of disease or injury did not significantly affect either U(crit) or post-exercise Mo2. We conclude that the ability of adult salmon to recover quickly from exercise may be a useful indicator of sublethal pathologies.     

Competition between Asian pink salmon (Oncorhynchus gorbuscha) and Alaskan sockeye salmon (O. nerka) in the North Pacific Ocean

The importance of interspecific competition as a mechanism regulating population abundance in offshore marine communities is largely unknown. We evaluated offshore competition between Asian pink salmon and Bristol Bay (Alaska) sockeye salmon, which intermingle in the North Pacific Ocean and Bering Sea, using the unique biennial abundance cycle of Asian pink salmon from 1955 to 2000. Sockeye salmon growth during the second and third growing seasons at sea, as determined by scale measurements, declined significantly in odd‐numbered years, corresponding to years when Asian pink salmon are most abundant. Bristol Bay sockeye salmon do not interact with Asian pink salmon during their first summer and fall seasons and no difference in first year scale growth was detected. The interaction with odd‐year pink salmon led to significantly smaller size at age of adult sockeye salmon, especially among younger female salmon. Examination of sockeye salmon smolt to adult survival rates during 1977–97 indicated that smolts entering the ocean during even‐numbered years and interacting with abundant odd‐year pink salmon during the following year experienced 26% (age‐2 smolt) to 45% (age‐1 smolt) lower survival compared with smolts migrating during odd‐numbered years. Adult sockeye salmon returning to Bristol Bay from even‐year smolt migrations were 22% less abundant (reduced by 5.9 million fish per year) compared with returns from odd‐year migrations. The greatest reduction in adult returns occurred among adults spending 2 compared with 3 years at sea. Our new evidence for interspecific competition highlights the need for multispecies, international management of salmon production, including salmon released from hatcheries into the ocean.     

Simulation of juvenile sockeye salmon (Oncorhynchus nerka) migrations in the Strait of Georgia, British Columbia

Previous research has documented two main migratory routes of juvenile sockeye salmon (Oncorhynchus nerka) through the Strait of Georgia, British Columbia, Canada, and large interannual variability in marine survival rates of the Chilko Lake stock. Simulation models were used to explore the influence of surface currents on the migratory route of juvenile sockeye salmon (smolts) through the Strait of Georgia. We used a model of downstream migration to generate daily numbers of Chilko Lake sockeye salmon smolts entering the Strait of Georgia, based on daily counts of smolts leaving the rearing lake. A numerical hydrodynamic model (driven by surface wind, tide, and Fraser River discharge) hindcasted surface currents in the Strait of Georgia on a 2 km × 2 km grid. A smolt migration model simulated fish moving through the Strait with different compass-oriented migratory behaviours (i.e. swimming speed and directional orientation) within the time-varying surface advection field. Results showed that surface currents within the Strait of Georgia can affect the migratory route of sockeye salmon smolts in spite of their large size (8 cm). Wind is the forcing mechanism primarily responsible for determining which migratory route would be used. Under prevailing wind conditions (i.e. toward the north-west), most sockeye salmon smolts would use the eastern migratory route; however, relatively brief south-eastward wind events (lasting about 2 days) would force most smolts into the western migratory route. Given the heterogeneity of food for salmon within the Strait, we hypothesize that wind-driven variability in the annual proportion of smolts that use the western and eastern migratory routes in the Strait of Georgia affects early marine survival rates of Fraser River sockeye salmon.     

Influence of the marine abundance of pink (Oncorhynchus gorbuscha) and sockeye salmon (O. nerka) on growth of Ozernaya River sockeye

The length and weight of Russian sockeye ( Oncorhynchus nerka ) returning to the Ozernaya River (Kamchatka) was substantially reduced in years when the ocean abundances of Kamchatkan pink ( O. gorbuscha ) and sockeye salmon were high. We found that the density-dependent reduction in sockeye growth on a per-capita basis was greater for sockeye than for pink salmon. However, the overall effect of pink salmon abundance on sockeye growth was greater because of the higher numerical abundance of pink salmon. The strongest statistical relationships were found for sockeye from separate age groups; pooled data combining all age classes were statistically insignificant. We estimate that, if pink salmon were absent, the most strongly affected age group of sockeye salmon (2.1 males) would weigh twice as much at maturity than if pink salmon populations from eastern and western Kamchatka were both simultaneously at peak observed abundances. Trophic competition in the ocean between pink and sockeye salmon can therefore have a significant influence on the productivity of sockeye populations for the most strongly affected age groups. These effects are large enough that they should be explicitly considered in the management of salmon populations.     

Seasonal changes of hormones and muscle enzymes in adult lacustrine masu (Oncorhynchus masou) and sockeye salmon (O. nerka)

The upstream migration of adult anadromous fishes is characterized by physiological changes in responses to reproductive and energetic challenges. This study analyzed the physiological responses of lake-resident anadromous masu salmon (Oncorhynchus masou) and sockeye salmon (O. nerka) to migration in order to determine if these fish might serve as a suitable model for ocean-running populations and to differentiate between physiological responses to reproduction and to exercise-linked aspects of migration. Reproductive (estradiol, testosterone, 11-ketotestosterone, 17α,20β-dihydroxy-4-pregnen-3-one) and metabolically-linked (thyroxine, triiodothyronine) hormones showed similar patterns to ocean-running anadromous populations. White muscle pyruvate kinase, lactate dehydrogenase and malate dehydrogenase decreased with the onset of spawning season while white muscle citrate synthase, β-hydroxyacetyl CoA dehydrogenase, phosphofructokinase and glutamate oxaloacetate transaminase did not, suggesting that the former group of enzymes are responding to reproductive or food intake signals while the second group, which typically change during anadromous migration, may be responding to exercise-linked aspects of migration. This revised version was published online in August 2006 with corrections to the Cover Date.     

Synergistic osmoregulatory dysfunction during salmon lice (Lepeophtheirus salmonis) and infectious hematopoietic necrosis virus co‐infection in sockeye salmon (Oncorhynchus nerka) smolts

While co‐infections are common in both wild and cultured fish, knowledge of the interactive effects of multiple pathogens on host physiology, gene expression and immune response is limited. To evaluate the impact of co‐infection on host survival, physiology and gene expression, sockeye salmon Oncorhynchus nerka smolts were infected with the salmon louse Lepeophtheirus salmonis (V?/SL+), infectious hematopoietic necrosis virus (IHNV; V+/SL?), both (V+/SL+), or neither (V?/SL?). Survival in the V+/SL+ group was significantly lower than the V?/SL? and V?/SL+ groups (p = 0.024). Co‐infected salmon had elevated osmoregulatory indicators and lowered haematocrit values as compared to the uninfected control. Expression of 12 genes associated with the host immune response was analysed in anterior kidney and skin. The only evidence of L. salmonis‐induced modulation of the host antiviral response was down‐regulation of mhc I although the possibility of modulation cannot be ruled out for mx‐1 and rsad2. Co‐infection did not influence the expression of genes associated with the host response to L. salmonis. Therefore, we conclude that the reduced survival in co‐infected sockeye salmon resulted from the osmoregulatory consequences of the sea lice infections which were amplified due to infection with IHNV.     

Site fidelity of spawning sockeye salmon (Oncorhynchus nerka W.) in the presence and absence of olfactory cues

Abstract –  We examined the site fidelity of spawning adult sockeye salmon ( Oncorhynchus nerka ) by tagging and releasing fish in the same stream reach (controls) and displacing them among different but nearby sites ( c . 50 m away). Three sites – two above a stream junction ('upper' reach and 'pond') and one below ('lower' reach) – allowed us to compare the behavior of salmon in the presence and absence of olfactory cues and habitat similarity. Most controls of both sexes (90%) remained in the immediate vicinity of the tagging and release site. When displaced downstream, where the odors of both the upper reach and the pond were detectable, most salmon returned to their former site (65%). Displaced sockeye were more likely to return to the pond from the lower reach than from the upper one ( P  = 0.05), consistent with olfactory orientation and the hypothesis that salmon prefer certain habitats. Salmon displaced from the upper to the lower reach were much more likely to return than those displaced to the pond ( P  < 0.01), consistent with the role of odors in orientation and inconsistent with the habitat choice hypothesis.     

Long-term changes in rearing habitat and downstream movement by juvenile sockeye salmon (Oncorhynchus nerka) in an interconnected Alaska lake system

Abstract –  In some populations the phenomenon of partial migration develops where some individuals stay in a given habitat rather than move with the migratory component. Depending on the selective pressures, the individuals that stay may be larger, smaller or similar in size to those that move. Freshwater movements of juvenile sockeye salmon ( Oncorhynchus nerka Walbaum) fry vary among and within populations, and can be complex, especially in interconnected lake systems. We examined variation of movement patterns by a sockeye salmon population in an interconnected lake system during a period of rapid natural habitat change and found that fry migrating downstream were shorter, had lower body condition, and were more likely ill and moribund compared with fish remaining in the lake. However, otolith microstructure measurements indicated that emigrants did not grow significantly slower than residents prior to downstream movement. We show that patterns (i.e., demography of migrants, timing of movement) of downstream movement have changed since the 1970s, corresponding to changes in rearing habitat. Our findings parallel the results with other salmonid species and are generally consistent with the paradigm that density-dependent interactions from declining habitat availability or quality result in the downstream movement of competitively inferior individuals, although the mechanisms governing downstream migration are unclear in this system.     

Oxidative stress in juvenile chinook salmon, Oncorhynchus tshawytscha (Walbaum)

Juvenile chinook salmon, Oncorhynchus tshawytscha (Walbaum), were held in 8–11°C freshwater, starved for 3 days and subjected to a low‐water stressor to determine the relationship between the general stress response and oxidative stress. Lipid peroxidation (LPO) levels (lipid hydroperoxides) were measured in kidney, liver and brain samples taken at the beginning of the experiment (0‐h unstressed controls) and at 6, 24 and 48 h after application of a continuous low‐water stressor. Tissue samples were also taken at 48 h from fish that had not been exposed to the stressor (48‐h unstressed controls). Exposure to the low‐water stressor affected LPO in kidney and brain tissues. In kidney, LPO decreased 6 h after imposition of the stressor; similar but less pronounced decreases also occurred in the liver and brain. At 48 h, LPO increased (in comparison with 6‐h stressed tissues) in the kidney and brain. In comparison with 48‐h unstressed controls, LPO levels were higher in the kidney and brain of stressed fish. Although preliminary, results suggest that stress can cause oxidative tissue damage in juvenile chinook salmon. Measures of oxidative stress have shown similar responses to stress in mammals; however, further research is needed to determine the extent of the stress–oxidative stress relationship and the underlying physiological mechanisms in fish.     

Marine and freshwater climatic factors affecting interannual variation in the timing of return migration to fresh water of sockeye salmon (Oncorhynchus nerka)

Interannual variation in the timing of the return migration to fresh water of adult sockeye salmon, Oncorhynchus nerka, from 46 populations throughout the species North American range was examined in a broad analysis of how timing patterns are affected by marine and freshwater conditions. Migration timing data (measured at various points along the migration, including just prior to freshwater entry, just after freshwater entry, and near the spawning grounds) were examined for correlations with sea‐surface temperatures (SST) prior to migration and to freshwater temperatures and flows during migration. Following a spring–summer period with warm SST, populations from southwestern Alaska tended to return early, Fraser River populations returned late, and populations from other regions showed no consistent patterns. Similarities between interannual timing of both nearby and distant populations indicated the presence of common or coincidental influences on timing. When riverine conditions related to timing, high flows and low temperatures were associated with late migrations, low flows and high temperatures were associated with early migrations. However, even counting stations at upriver locations showed correlations with SST. Notwithstanding some inconsistencies among the many populations examined and the indirect nature of the inferences, the results supported the hypotheses that (i) interannual variations in salmon distributions at sea reflect temperature conditions, and (ii) the date when salmon initiate homeward migration is a population‐specific trait, largely unaffected by the fish's location at sea.     

On the effect of the Kasatoshi volcano on the large return of sockeye salmon (Oncorhynchus nerka) to the Fraser River in 2010

The hypothesis on the beneficial effect of volcanic ash on sockeye salmon (Oncorhyncus nerka) survival, advanced in an earlier paper (Parsons and Whitney, 2012), is discussed further in the light of a response on this subject by McKinnell (Fish. Oceanogr., 22, 2013, 337–344). We elaborate on a number of points which challenge our original hypothesis.     

Simulated maternal pre‐spawning stress affects offspring's attributes in farmed Atlantic salmon Salmo salar (Linnaeus, 1758)

In fish hormones are released into the nutritive yolk sac during oogenesis in quantities that mirror female plasma levels, thus implying a potential for the maternal endocrine state at spawning to affect offspring characteristics. In the present study, mature female Atlantic salmon, Salmo salar, were given intraperitoneal cortisol implants to investigate potential impacts of simulated stress on offspring ontogeny. Maternal cortisol levels reduced fertilization success and affected several offspring characters: lowered initial survival rates, impaired growth early in life and increased prevalence of morphological abnormalities in adult individuals. In addition, offspring from cortisol administered females displayed increased locomotor activity in an acute confinement test. These results suggest that developmental trajectories of salmon offspring can be considerably altered if their mothers experience severe stress during the final stages of gametogenesis. The present findings may have conceptual and applied ramifications as they demonstrate a mechanism that links the maternal environment to subsequent viability of the progeny.     

An investigation of the biological basis of return variability for sockeye salmon (Oncorhynchus nerka) from Great Central and Sproat lakes,Vancouver Island

We tested whether variations in stock characteristics (spawner and smolt abundance) and biotic conditions (prey variability, predation, competition) during the early marine period explained variations in the return of sockeye salmon (Oncorhynchus nerka) to Great Central and Sproat lakes, adjacent lakes on the west coast of Vancouver Island. There are two freshwater age groups in each lake; fish spend 1 or 2 yrs in freshwater after hatching. We tested the influences of stock and biotic factors on the return of each of the two age groups from each of the two lakes. Results of regression analyses showed that prey biomass variability best explained the variation in return for all lake‐age groups. Euphausiid (Thysanoessa spinifera) and cladoceran (Evadne) prey biomass variability explained between 0.75 and 0.95 (adjusted R²) of the variation in return. There appear to be instances of a mismatch between the seasonality of prey productivity and the apparent critical period of feeding for juvenile sockeye.     

Challenges for the Kasatoshi volcano hypothesis as the cause of a large return of sockeye salmon (Oncorhynchus nerka) to the Fraser River in 2010

In August 2008 the Kasatoshi volcano in the Aleutian archipelago erupted. Prevailing winds carried volcanic ash to the Gulf of Alaska, where its soluble iron dissolved and initiated a widespread phytoplankton bloom. Two years later, the abundance of sockeye salmon (Oncorhynchus nerka) returning to spawn in the Fraser River was larger than any observed since 1913. Kasatoshi's influence on growth and survival has been proposed as the ultimate cause of the abundant return. However, when relevant data are brought to bear on the hypothesis, it shows that: (1) survival of the abundant sockeye salmon cohort was unremarkable when compared with the historical record; (2) without an accompanying volcano, survival of the returns in 2011 was about the same as in 2010; (3) parental abundance that spawned the abundant return in 2010 was the sixth largest since 1948; (4) during their first summer at sea, sockeye salmon are not known to migrate in the offshore region where the anomalous chlorophyll bloom occurred; (5) an older cohort that was likely exposed to the chlorophyll bloom had the second lowest productivity on record when it returned in 2009; (6) immature sockeye salmon do not feed on diatoms, so any trophodynamic benefit derived from excess chlorophyll in mid‐to late August 2008 would have to have found a rapid trophic pathway to sockeye salmon on the continental shelf; and (7) no other populations of sockeye salmon or other species of salmon that are known to rear in the same region had unexpectedly high returns.     

山女鳟早期发育及低温耐性观察

将发育积温242℃.d的山女鳟发眼卵置山溪中进行流水孵化。在日均水温4.8℃环境下,发育积温达382℃.d时开始有少数鱼苗孵出。此后在日均2.3~1.5℃,最低0.2℃环境下历时36d,发育积温达456℃.d时全部孵化出膜,孵化率90.2%。最早出膜的孵化稚鱼在日均水温1.5~3.7℃,最低0.2℃环境下历时93d,发育积温达668℃.d时开始上浮。受精后172d发育积温达762℃.d时全部上浮,上浮率77.3%。驯饲一个月的稚鱼育成率63.2%。雏鱼孵化及形态机能发育正常,表明山女鳟在日均水温4.8~1.5℃,最低0.2℃的低温环境中可以正常地进行早期发育。     

Freshwater habitat associations between pink (Oncorhynchus gorbuscha), chum (O. keta) and Chinook salmon (O. tshawytscha) in a watershed dominated by sockeye salmon (O. nerka) abundance

To understand the interplay between habitat use and contemporary anadromous Pacific salmon, Oncorhynchus spp., distributions we explored the habitat associations of three species, pink (O. gorbuscha), chum (O. keta) and Chinook salmon (O. tshawytscha) in streams of the Wood River system of Bristol Bay, Alaska, where sockeye salmon (O. nerka) are numerically dominant. We developed models to investigate the occurrence of nondominant salmon in relation to habitat characteristics and sockeye salmon density, using four decades of salmon presence and abundance data. The frequency of occurrence and abundance of nondominant species increased with watershed drainage area and stream depth and decreased with sockeye salmon density. The range of occurrence varied from nonexistent to perennial for the other species in sockeye‐dominated streams. Increasing watershed area resulted in larger stream habitat area and deeper habitats, allowing for the sympatric occurrence and persistence of all salmon species. The relationships between habitat and the presence of these Pacific salmon help define their requirements but also remind us that the patterns of presence and absence, within the overall ranges of salmon species, have yet to be fully understood.     

A matter of timing: the role of ocean conditions in the initiation of spawning migration by late‐run Fraser River sockeye salmon (Oncorhynchus nerka)

Year 1995 marked the start of a major shift to earlier river entry of late‐run Fraser River sockeye salmon (Oncorhynchus nerka) en route to the spawning grounds. Earlier entry has typically been accompanied by considerably greater in‐river mortality. We examine this behavioral change using correlation analyses between the entry timing of the Adams River and Weaver Creek stocks and the surface marine conditions encountered by the stocks during their homing migration from the northeast Pacific several months earlier. For Adams stocks, maximum correlation is between entry timing and offshore winds, such that the weaker the wind stress in the direction of the prevailing surface currents in early July, the earlier the river entry in late summer. For Weaver stocks, maximum correlation is with salinity, such that the lower the surface salinity along the coast in August, the earlier the river entry. We hypothesize that oceanic changes lead to changes in late‐run sockeye physiology which then leads to changes in behavior. Physiological changes are postulated to arise from two types of preconditioning: Type‐1 occurs in the offshore region, whereby the weaker the prevailing currents that normally hinder eastward migration, the more endogenous energy available for maturation and the earlier the river entry. Type‐2 occurs in coastal regions, whereby the lower the salinity, the more rapid the osmoregulatory adaptation to freshwater (and possible susceptibility to water‐borne pathogens) and the earlier the entry. Results suggest that the earlier entry that began in the mid‐1990s is linked to weaker ocean currents and lower coastal salinities.     

Sex differences in metabolic rate and swimming performance in pink salmon (Oncorhynchus gorbuscha): the effect of male secondary sexual traits

Do secondary sexual traits, such as large dorsal hump and hooked snout, decrease the swimming efficiency of male pink salmon during freshwater migration? This is the first study to address the effects of secondary sexual traits in pink salmon on oxygen uptake and swimming capacity. We conducted a laboratory experiment using a swimming respirometer and a field study using electromyogram (EMG) telemetry in the Shibetsu River, Hokkaido, Japan. We compared the relationship between MO₂ (mg O₂·kg^?1·h^?1) and swimming velocity U (m·s^?1) in male and female fish, and also investigated the effects of morphological traits (secondary sexual characters) on the relationship between MO₂ (mg O₂·kg^?1·h^?1) and swimming velocity U (m·s^?1). Additionally, we compared energy costs and swimming behaviour during upstream migration between male and female pink salmon. The laboratory experiment revealed that MO₂ exponentially increased with increasing U; this increase was described by MO₂ = 167.9e^1.23U for males and 144.9e^1.14U for females. Linear mixed models found that hump height and the upper jaw length in males significantly and positively affected the relationship between MO₂ and U; no effect was found in females. The field study found that swimming velocity for both sexes estimated from EMG calibration was lower than optimal swimming velocity (U_opt) calculated from the laboratory experiment. We suggest that pink salmon in the Shibetsu River do not swim at the optimal swimming velocity because of the short migration distance involved (20 km).     

Relationship between dietary lipid source, oxidative stress, and the physiological response to stress in sub-yearling chinook salmon (Oncorhynchus tshawytscha)

Relationships between dietary lipid source, stress, and oxidative stress were examined in juvenile chinook salmon (Oncorhynchus tshawytscha). Four different experimental diets were used: menhaden oil (MHO; elevated 20:5n-3 and 22:6n-3), soybean oil (SBO; elevated 18:2n-6), linseed oil (LSO; elevated 18:3n-3), and a mixture of 55% linseed oil and 45% soybean oil (MIX; approximately equal levels of 18:2n-6 and 18:3n-3). Juvenile salmon (initial body weight of 16.0 g) were fed experimental diets for 12 weeks (early March to early June). At the end of feeding, fish subjected to a low-water stressor for 96 h had greater liver and brain lipid peroxidation compared to unstressed controls; peroxidation was not influenced by diet. Diet and stress affected plasma cortisol levels. Stressed fish fed SBO had the greatest cortisol concentrations, followed by MIX, MHO, and LSO (mean concentrations for the SBO and LSO diets differed significantly). The cortisol response to stress may have been influenced by the ratio of prostaglandin 1- and 2-series to prostaglandin 3-series precursor fatty acids provided by the different diets. The results of this study suggest a connection between the physiological response to stress, dietary lipid quality, and oxidative stress. This is the first evidence of such a relationship in fish. Abbreviations: AA - arachidonic acid; ACTH - adrenocorticotropin; BHT - butylated hydroxytoluene; BLPO - brain lipid peroxidation; dGLA - dihomo-γ-linolenic acid; DHA - docosahexanoic acid; EPA - eicosapentanoic acid; FER - feed efficiency ratio; FOX - ferrous oxidation-xylenol orange; GLA -γ-linolenic acid; LA - linoleic acid; LCO3 - long-chain n-3 polyunsaturated fatty acids; LLPO - liver lipid peroxidation; LN - linolenic acid; LPO - lipid peroxidation; LSO - linseed oil; MHO - menhaden oil; MIX - 55% linseed oil + 45% soybean oil; PC - plasma cortisol; PG - prostaglandin(s); PGE₂- prostaglandin E₂; PUFA - polyunsaturated fatty acid; SBO - soybean oil. This revised version was published online in July 2006 with corrections to the Cover Date.