Juvenile Spring Chinook Salmon Research Articles

Comparisons of donor stray percentages between hatchery‐ and natural‐origin Chinook Salmon and steelhead in the upper Columbia watershed

AbstractObjectiveArtificial propagation of Pacific salmon Oncorhynchus spp. is commonly used to achieve conservation and harvest goals. However, unintended effects of artificial propagation, such as high donor stray percentages, can reduce numbers of adults that return to target areas and also contribute spawners to different populations where they are undesirable. Until recently, it was difficult to assess if hatchery‐origin fish stray rates were atypical because few estimates of stray rates of natural‐origin fish were available. We sought to fill that gap by comparing donor stray percentages of hatchery‐ and natural‐origin Chinook Salmon O. tshawytscha and steelhead O. mykiss from the same locations.MethodsWe used 29,885 last passive integrated transponder tag detections of adult fish to estimate and compare donor stray percentages of hatchery‐origin and natural‐origin Chinook Salmon and steelhead in the upper Columbia River watershed between 2002 and 2018.ResultDonor stray percentages of hatchery‐origin spring, summer, and fall Chinook Salmon and steelhead were <0.3% at the upper Columbia basin scale and similar to natural‐origin donor stray percentages. Only steelhead donor stray percentages were higher for hatchery‐origin adults at the subbasin scale than natural‐origin counterparts and were <22% for all taxa. The percentage of hatchery‐origin steelhead and spring Chinook Salmon released in tributaries were detected at nontarget areas at higher percentages (<63%) than natural‐origin counterparts born in these tributaries. Returning hatchery‐origin and natural‐origin Chinook Salmon and steelhead generally strayed in an upstream direction in similar proportions. Juvenile spring Chinook Salmon that were moved 14–391 km from centralized hatcheries to tributaries for overwintering or final acclimation strayed at a much higher rate than those that completed their incubation, rearing, and acclimation at a single location, but this did not occur with steelhead. Other adaptive management actions that were implemented to reduce straying produced mixed results. A high proportion of stray hatchery‐origin spring Chinook Salmon initially homed to tributary weirs.ConclusionDonor stray percentages of hatchery‐origin Chinook Salmon and steelhead were generally not higher than natural‐origin donor stray percentages at larger spatial scales (e.g., upper Columbia basin and subbasin) but were higher at smaller spatial scales (e.g., tributaries). A variety of approaches can be considered to reduce undesirable production of strays, but most of them involve difficult management trade‐offs.

Effects of rearing system on growth responses and saltwater tolerance in spring Chinook Salmon (Oncorhynchus tshawytscha)

Pacific salmon (Oncorhynchus spp.) produced in United States conservation hatcheries are commonly reared in tanks and raceways supplied with single-pass water. As controlled studies comparing water reuse vs. traditional single-pass aquaculture systems are limited, we conducted a 20-week growth trial followed by a one-week saltwater challenge to compare growth, survival and saltwater tolerance of juvenile spring Chinook salmon (O. tshawytscha, 5.2 g initial weight) reared in single-pass rectangular tanks (hereafter rectangular tanks), single-pass circular tanks (hereafter circular tanks), or in circular tanks of recirculating aquaculture systems (RAS, 3% constant makeup water on a flow basis) or partial recirculating aquaculture systems (PRAS, 20% constant makeup water on a flow basis). Water volume provided to rearing tanks did not differ among systems, but water velocities in the circular tanks and in the RAS and PRAS fish culture tanks were higher than in the rectangular tanks. Dissolved oxygen levels declined throughout the study in all systems and were significantly lower in RAS than in the single-pass systems. By week 16, ammonia levels were significantly reduced while nitrite‑nitrogen (NO2-N) and nitrate‑nitrogen (NO3-N) levels were significantly elevated in RAS compared with single-pass systems.Salmon grown in rectangular tanks exhibited significantly lower weight gain and feed efficiency (FE; g gain/g feed) compared with fish reared in the other systems. Survival of salmon grown in the rectangular tanks (99.1%) also was significantly lower than that of fish reared in circular tanks (100%) or PRAS (100%), but was not different from that of fish reared in RAS (99.8%). Survival during the saltwater challenge was significantly reduced in salmon that were reared during the growth trial in rectangular tanks (70%) compared with that of fish that were reared in the other systems (92–96%). Results of this study suggest lower growth and survival of salmon reared in rectangular tanks may be related to reduced water velocity and that RAS and PRAS may be appropriate for rearing spring Chinook salmon for conservation purposes.

A correlation between seasonally changing photoperiod, whole body lipid, and condition factor in juvenile spring Chinook salmon (Oncorhynchus tshawytscha).

The regulation of lipid stores is a central process for the physiology and ecology of fishes. Seasonal variation in lipid stores has been directly linked to survival of fishes across periods of food deprivation. We assessed whether a seasonally changing photoperiod was correlated to seasonal changes in energetic status to help better understand these important processes. Groups of first feeding Chinook salmon fry were introduced to a seasonal photoperiod cycle, but the point of entrance into the seasonal cycle varied from near the winter solstice (December), to either side of the spring equinox (February & May). Temperature and feeding rate were similar for all treatments. Subsequently, condition factor and whole body lipid content were assessed through a seasonal progression. Throughout most of the experiment, length and weight did not differ between the different photoperiod treatments, however whole body lipid and Fulton's condition factor did. Furthermore, changes in both whole body lipid and Fulton's condition factor in all treatment groups followed a similar seasonal pattern that was inversely related to day length (highest K and lipid levels found during days with the least light). These results suggest that regardless of age or size, there is a correlation between seasonal changes in photoperiod and changes in body composition in juvenile Chinook salmonids.

Dietary tetradecylthioacetic acid supplementation during the fall prevents an increase in body lipid levels but does not influence precocious male maturation rate in juvenile spring Chinook salmon

Precocious maturation of male fish as two-year-olds occurs at significant rates in spring Chinook salmon hatchery programmes in the Columbia River Basin, representing a loss of production. Precocious maturation is thought to occur due to elevated lipid and other energy reserves in hatchery fish during critical periods for the regulation of gonadal development. To determine whether modification of lipid reserves affects precocious maturation rates in juvenile spring Chinook salmon, we administered feed supplemented with tetradecylthioacetic acid (TTA; a supplement that upregulates lipid oxidation) during the fall critical period one year prior to maturation of precocious individuals. Maturation status was determined the following spring from plasma 11-ketotestosterone levels. TTA administration reduced body lipid levels relative to controls but did not reduce precocious maturation rate. Fish growth was reduced during the TTA feeding period but recovered after fish were returned to a standard diet. No differences in the effect of TTA were found between male and female fish. Our results show that TTA can be used to manipulate body lipid levels in juvenile Chinook salmon but provide no support for a major role of fall body lipid levels in regulating precocious maturation in juvenile male spring Chinook salmon under hatchery conditions.

Threats to Rearing Juvenile Chinook Salmon from Nonnative Smallmouth Bass Inferred from Stable Isotope and Fatty Acid Biomarkers

AbstractNonnative Smallmouth BassMicropterus dolomieuare increasingly sympatric with juvenile spring Chinook SalmonOncorhynchus tshawytschain the rivers of western North America. Understanding the potential effects of introduced Smallmouth Bass is essential to efficiently direct salmon management efforts, especially given the potential for upstream range expansion of Smallmouth Bass in response to the climate‐induced warming that many rivers may experience. However, the predatory and competitive threats of Smallmouth Bass to juvenile salmonids remain largely unexamined, particularly in salmon rearing areas. To address this knowledge gap, we collected stable isotope (δ13C and δ15N) and fatty acid data to assess the trophic role of Smallmouth Bass in the upstream reaches of the North Fork John Day River, a tributary of the Columbia River where the upstream invasion extent of Smallmouth Bass co‐occurs with the native predator Northern Pikeminnow and river‐rearing juvenile Chinook Salmon. We found that Smallmouth Bass and Northern Pikeminnow occupy divergent dietary niches, and there was little evidence of a strong predation or competition threat to juvenile Chinook Salmon from either predator. In addition, we found a disproportionate reliance on autochthonous resources across the entire community and low isotopic uniqueness, suggesting potential competition among the broader fish community given the scarcity of resources. Importantly, this study focused on the overlap between the upstream‐most habitats of encroaching Smallmouth Bass and downstream‐most habitats of juvenile Chinook Salmon. Therefore, the relative scarcity of rearing salmon in comparison with other available prey in this zone may limit current predation threats. The results from this study help guide resource‐limited managers that are tasked with conserving and restoring native salmonid populations.

GrowChinook: an optimized multimodel and graphic user interface for predicting juvenile Chinook salmon growth in lentic ecosystems

Linked foraging and bioenergetics models allow for increased understanding of fish growth potential and behavior by incorporating prey availability coupled to environmental conditions including temperature and prey visibility. To inform our understanding of growth and vertical migration patterns of Chinook salmon (Oncorhynchus tshawytscha) inhabiting lentic ecosystems, we linked foraging and bioenergetics models to create GrowChinook ( http://growchinook.fw.oregonstate.edu/ ). This multimodel design and optimization routine has broad applications in examining growth potential and predicting habitat use in stratified environments. We demonstrate the use of GrowChinook for the spring–summer rearing period in three Willamette River basin reservoirs, Oregon, USA. These reservoirs support juvenile spring Chinook salmon that exhibit a novel reservoir-reared life history that includes larger juvenile fish compared with nearby stream-reared subyearlings. Model outputs of predicted growth and depth use patterns based on observed prey distributions and environmental conditions were corroborated by observed empirical size and growth data from other years. Our simulations support diel vertical migration as a tactic that increases growth potential and contribute to understanding juvenile Chinook salmon growth in stratified systems.

Fish Occurrence in a Seasonally Inundated Floodplain of the Willamette River, Oregon

The dynamic nature of large rivers is often diminished by anthropogenic alterations resulting in simplified stream networks with decreased floodplain connectivity and ecological function which adversely impact native organisms. However, little is known about the importance of large river floodplains to fish communities in the Pacific Northwest, especially during winter high flows. Our objectives were to document seasonal use of a Willamette River floodplain for native and non-native fish by measuring: 1) fish community characteristics (species richness, native versus non-native status, relative abundance), 2) spawning and rearing, 3) timing of use and movement, and 4) use by federally protected juvenile spring Chinook salmon (Oncorhynchus tshawytscha). During fall 2011 through spring 2012, a floodplain was sampled with a backpack electrofisher and out-migrant trap. A total of 12 native and 11 non-native species were detected. During nine electrofishing samples, 691 fish were collected, of which 95% were native. An estimated 42,297 fish were captured by the out-migrant trap; 98% of which were native and most were age-0 threespine stickleback (Gasterosteus aculeatus). Native species were detected on the floodplain prior to non-native species and tended to emigrate from the floodplain before non-native species, leading to a higher potential of stranding for non-native species as waters recedes. This study documents use of floodplain habitat by native and non-native fish species for seasonal flood refuge, rearing and spawning. Our results demonstrate native fish communities could potentially benefit from conservation of existing floodplains and restoration of floodplains changed by land use practices and altered flow regimes.

Egg size and emergence timing affect morphology and behavior in juvenile Chinook Salmon, Oncorhynchus tshawytscha.

Variation in early life history traits often leads to differentially expressed morphological and behavioral phenotypes. We investigated whether variation in egg size and emergence timing influence subsequent morphology associated with migration timing in juvenile spring Chinook Salmon, Oncorhynchus tshawytscha. Based on evidence for a positive relationship between growth rate and migration timing, we predicted that fish from small eggs and fish that emerged earlier would have similar morphology to fall migrants, while fish from large eggs and individuals that emerged later would be more similar to older spring yearling migrants. We sorted eyed embryos within females into two size categories: small and large. We collected early and late‐emerging juveniles from each egg size category. We used landmark‐based geometric morphometrics and found that egg size appears to drive morphological differences. Egg size shows evidence for an absolute rather than relative effect on body morphology. Fish from small eggs were morphologically more similar to fall migrants, while fish from large eggs were morphologically more similar to older spring yearling migrants. Previous research has shown that the body morphology of fish that prefer the surface or bottom location in a tank soon after emergence also correlates with the morphological variations between wild fall and spring migrants, respectively. We found that late‐emerging fish spent more time near the surface. Our study shows that subtle differences in early life history characteristics may correlate with a diversity of future phenotypes.

Juvenile life-history diversity and population stability of spring Chinook salmon in the Willamette River basin, Oregon

Migratory and rearing pathways of juvenile spring Chinook salmon (Oncorhynchus tshawytscha) were documented in the Willamette River basin to identify life histories and estimate their contribution to smolt production and population stability. We identified six primary life histories that included two phenotypes for early migratory tactics: fry that migrated up to 140–200 km shortly after emergence (movers) and fish that reared for 8–16 months in natal areas (stayers). Peak emigration of juvenile salmon from the Willamette River was in June–July (subyearling smolts), March–May (yearling smolts), and November–December (considered as “autumn smolts”). Alternative migratory behaviors of juvenile salmon were associated with extensive use of diverse habitats that eventually encompassed up to 400 rkm of the basin, including tributaries in natal areas and large rivers. Juvenile salmon that reared in natal reaches and migrated as yearlings were the most prevalent life history and had the lowest temporal variability. However, the total productivity of the basin was increased by the contribution of fish with dispersive life histories, which represented over 50% of the total smolt production. Life-history diversity reduced the variability in the total smolt population by 35% over the weighted mean of individual life histories, providing evidence of a considerable portfolio effect through the asynchronous contributions of life histories. Protecting and restoring a diverse suite of connected habitats in the Willamette River basin will promote the development and expression of juvenile life histories, thereby providing stability and resilience to native salmon populations.

Geochemical signatures in fin rays provide a nonlethal method to distinguish the natal rearing streams of endangered juvenile Chinook Salmon Oncorhynchus tshawytscha in the Wenatchee River, Washington

Rebuilding fish populations that have undergone a major decline is a challenging task that can be made more complicated when estimates of abundance obtained from physical tags are biased or imprecise. Abundance estimates based on natural tags where each fish in the population is marked can help address these problems, but generally requires that the samples be obtained in a nonlethal manner. We evaluated the potential of using geochemical signatures in fin rays as a nonlethal method to determine the natal tributaries of endangered juvenile spring Chinook Salmon in the Wenatchee River, Washington. Archived samples of anal fin clips collected from yearling smolt in 2009, 2010 and 2011 were analyzed for Ba/Ca, Mn/Ba, Mg/Ca, Sr/Ca, Zn/Ca and 87Sr/86Sr by inductively coupled plasma mass spectrometry. Water samples collected from these same streams in 2012 were also quantified for geochemical composition. Fin ray and water Ba/Ca, Sr/Ca, and 87Sr/86Sr were highly correlated despite the samples having been collected in different years. Fin ray Ba/Ca, Mg/Ca, Sr/Ca, Zn/Ca and 87Sr/86Sr ratios differed significantly among the natal streams, but also among years within streams. A linear discriminant model that included Ba/Ca, Mg/Ca, Sr/Ca, and 87Sr/86Sr correctly classified 95% of the salmon to their natal stream. Our results suggest that fin ray geochemistry may provide an effective, nonlethal method to identify mixtures of Wenatchee River spring Chinook Salmon for recovery efforts when these involve the capture of juvenile fish to estimate population abundance.

Salinity effects on plasma ion levels, cortisol, and osmolality in Chinook salmon following lethal sampling

Studies on hydromineral balance in fishes frequently employ measurements of electrolytes following euthanasia. We tested the effects of fresh- or salt-water euthanasia baths of tricaine mesylate (MS-222) on plasma magnesium (Mg2+) and sodium (Na+) ions, cortisol and osmolality in fish exposed to saltwater challenges, and the ion and steroid hormone fluctuations over time following euthanasia in juvenile spring Chinook salmon (Oncorhynchus tshawytscha). Salinity of the euthanasia bath affected plasma Mg2+ and Na+ concentrations as well as osmolality, with higher concentrations in fish euthanized in saltwater. Time spent in the bath positively affected plasma Mg2+ and osmolality, negatively affected cortisol, and had no effect on Na+ concentrations. The difference of temporal trends in plasma Mg2+ and Na+ suggests that Mg2+ may be more sensitive to physiological changes and responds more rapidly than Na+. When electrolytes and cortisol are measured as endpoints after euthanasia, care needs to be taken relative to time after death and the salinity of the euthanasia bath.

Biotic and Abiotic Influences on Abundance and Distribution of Nonnative Chinook Salmon and Native ESA-Listed Steelhead in the Wind River, Washington

Abstract Biotic and abiotic factors influence fish populations and distributions. Concerns have been raised about the influence of hatchery fish on wild populations. Carson National Fish Hatchery produces spring Chinook salmon Oncorhynchus tshawytscha in the Wind River, Washington, and some spawn in the river. Managers were concerned that Chinook salmon could negatively affect wild steelhead O. mykiss and that a self-sustaining population of Chinook salmon may develop. Our objectives were to assess: 1) the distribution and populations of juvenile spring Chinook salmon and juvenile steelhead in the upper Wind River; 2) the influence of stream flow and of each population on the other; and 3) if Chinook salmon populations were self-sustaining. We snorkeled to determine distribution and abundance. Flow in the fall influenced upstream distribution and abundance of juvenile Chinook salmon. Juvenile Chinook salmon densities were consistently low (range 0.0 to 5.7 fish 100 m-2) and not influenced by number of spa...

Restoration Monitoring on the McKenzie River, Oregon

In the spring of 2012, we, the Stream Stewardship Team from the University of Oregon’s Environmental Leadership Program (ELP), conducted post-monitoring surveys at a side channel of the Middle McKenzie River (side channel 4) to compare with baseline monitoring data collected by the 2011 ELP Restoration Stewardship Team. The goal of this restoration project was to enhance juvenile spring Chinook salmon (Oncorhynchus tshawytscha) rearing habitat within the channel. In 2011 the U.S. Forest Service placed large woody debris (LWD) in five sections of the channel after baseline monitoring to increase the complexity of the streambed within the channel and to create a distribution of sediment optimal for salmon spawning habitat. We conducted pebble counts, cross-channel surveys, and a longitudinal profile of the stream to observe changes since the addition of LWD. Median pebble size decreased downstream of the LWD placements at gravel count 1 and increased upstream at gravel count 2. The percent of embedded sediment decreased at both gravel count sites. We also detected noticeable changes in the stream morphology at four of the five cross-sectional surveys as well as along the longitudinal profile. Sediment size distribution and the formation of pools at the downstream end of the channel showed an initial change in stream morphology since 2011, but further monitoring is warranted in order to fully assess the effects of LWD on streambed complexity and salmon spawning habitat.

Baffled and Standard Raceways: A Comparison of Juvenile Spring Chinook Salmon Performance and Smolt‐to‐Adult Survival

AbstractWe compared on‐station mortality, growth (mm), feed conversion, health parameters, and smolt‐to‐adult survival rate of spring Chinook salmon Oncorhynchus tshawytscha reared in baffled and standard (unbaffled) raceways. Fish reared in baffled raceways survived from release to adulthood at a rate 0.85 times that of fish reared in unbaffled raceways. There was no difference in percent on‐station mortality (range, 0.00–0.001), health, or average length gained (1–12 mm) between fish reared in baffled and unbaffled raceways. Average feed conversion was constant (1.20–2.25) throughout the period of juvenile rearing and was similar between fish reared in baffled and unbaffled raceways, a finding supported by adiposomatic and hepatosomatic indices. Overall, we found similar on‐station performance between fish reared in baffled and unbaffled raceways. The difference between SARs of fish reared in baffled versus unbaffled raceways was not statistically significant (P = 0.08). However, it is suggestive of a biological difference between the two treatments. The self‐cleaning characteristics of baffled raceways free up a substantial amount of hatchery personnel time to attend to other duties, which ultimately reduces the annual operation budget for any facility. In the end, the self‐cleaning feature of baffled raceways needs to be weighed against any advantage in adult survival of fish reared in unbaffled raceways.

A spatially and temporally explicit risk assessment for salmon from a prey base exposed to agricultural insecticides

This risk assessment applied a framework for determining probable co-occurrence of juvenile spring Chinook salmon (Oncorhynchus tshawytscha) with agricultural pesticides in the Willamette Basin, Oregon (Teply et al. this issue) to characterize risk to the threatened population. The assessment accounted for spatial and temporal distribution of 6 acetylcholinesterase-inhibiting insecticides in salmonid habitat within the basin and their relative contributions to mixture toxicity estimated from chemical monitoring data. The 6 insecticides were chlorpyrifos, diazinon, malathion, carbaryl, carbofuran, and methomyl. Seasonal distributions of the juvenile salmon prey base across the basin were determined and compared to co-occurrence with the insecticide mixture to determine the probability of prey reduction and reduced production of juvenile fish. Probability of effect on freshwater aquatic invertebrates was based on acute toxicity species sensitivity distributions (normalized to the most potent compound, chlorpyrifos) using a novel approach to apply the toxicological concept of concentration addition to species sensitivity distributions with differing slopes. The chlorpyrifos distribution was then used to determine relative sensitivity among various species tested within the important taxa making up the prey base. A prey base index was devised, incorporating diet composition and prey availability, to evaluate the indirect effects of the insecticide mixture on juvenile salmon production occurring as a result of a reduction in the prey base. Our analysis targeted fish use of backwater and off-channel habitat units, because they generally coincide with agricultural lands in lowlands and represent shallow habitat with limited water exchange. The percentage of agricultural land use within 300 m of critical habitat stream reaches was used to scale chemical measurement data from a site with high agricultural land use across the full extent of the basin to provide estimates of chemical exposure in each reach. Seasonal impacts were evaluated from mean monthly concentrations. Stressor impact on 5 key taxa was evaluated at each time step and for each reach, and the outcome was compared to a conservation threshold assigned to the prey base index. Only 13% of juveniles reared in backwater, off-channel habitat within 300 m of agricultural land. Percent reduction of carrying capacity as a consequence of reduced prey was estimated to be 5% over the entire brood year. This can be considered lost capacity that is probably compensated elsewhere via increased occupancy (emigration to other habitat units within the reach), which is not accounted for in the model.

Ecology of Winter Concealment Behavior of Juvenile Spring Chinook Salmon in the Grande Ronde River Basin, Oregon

We characterized winter concealment behavior (WCB) for juvenile spring Chinook salmon (Oncorhynchus tshawytscha) from October through January in three study streams of the Grande Ronde River Basin, Oregon. The Nocturnal Index (NI), the frequency of fish using WCB, increased significantly as mean daily water temperature decreased. WCB was negatively associated with mean daily water temperature in all three streams, and positively associated with fish size in Catherine Creek and the Lostine River. WCB was not significantly associated with fish density in any of the three streams. Both the NI and detections of concealed fish indicated that fish were concealing amid interstitial spaces during the day and emerging at night as early as October–November, yet no population fully exhibited WCB during any month sampled. Although low water temperature influenced WCB in the Grande Ronde River Basin, other ecological factors affected the behavior because not all fish used WCB even when mean daily water temperatures were < 1°C.

Preliminary examination of oxidative stress in juvenile spring Chinook salmon Oncorhynchus tshawytscha of wild origin sampled from transport barges

Migrating juvenile wild Chinook salmon Oncorhynchus tshawytscha, collected and loaded onto transport barges at Lower Granite Dam on the Snake River, were sampled from barges at John Day Dam, 348 km downstream, at 5 day intervals beginning in late April and ending in late May. An increase in lipid peroxidation and decrease in vitamin E in liver were observed from early to late in the barge transportation season. These changes seemed unrelated to changes in plasma cortisol or corresponding glucose levels, which declined from early to late in the season, or the concentration of n-3 highly unsaturated fatty acid (HUFA) concentrations in tissue but may be related to water temperature, which increased during the transport season, or other changes associated with the parr-smolt transformation.

Relationship of winter concealment habitat quality on pool use by juvenile spring Chinook salmon (Oncorhynchus tshawytscha) in the Grande Ronde River Basin, Oregon USA

Winter concealment habitat quality was assessed and its use by juvenile spring Chinook salmon (Oncorhynchus tshawytscha) quantified in three hatch- ing areas of the Grande Ronde River Basin, Oregon USA. Fish densities were significantly higher in pools with a higher winter concealment habitat index than pools with a lower index. The mean fork length and mean growth rate of fish did not differ between pools with a higher or lower winter concealment habitat index, even though residual fish were significantly larger than fish that emigrated. Biomass-density was significantly higher in pools with a higher winter concealment habitat index than pools with a lower index in all three hatching areas. Biomass-density was positively associated with the amount of cobble substrate (10-24.9 cm/m 2 ) in all three hatching areas, and inversely associated with embeddedness in two of the hatching areas. Results of this study indicate that enhancing winter concealment habitat could improve habitat quality resulting in increased carrying capacity and winter usage by juvenile spring Chinook salmon.

Effect of dietary α‐tocopherol + ascorbic acid, selenium, and iron on oxidative stress in sub‐yearling Chinook salmon (Oncorhynchus tshawytscha Walbaum)

A three-variable central composite design coupled with surface-response analysis was used to examine the effects of dietary alpha-tocopherol + ascorbic acid (TOCAA), selenium (Se), and iron (Fe) on indices of oxidative stress in juvenile spring Chinook salmon. Each dietary factor was tested at five levels for a total of fifteen dietary combinations (diets). Oxidative damage in liver and kidney (lipid peroxidation, protein carbonyls) and erythrocytes (erythrocyte resistance to peroxidative lysis, ERPL) was determined after feeding experimental diets for 16 (early December) and 28 (early March) weeks. Only TOCAA influenced oxidative stress in this study, with most measures of oxidative damage decreasing (liver lipid peroxidation in December and March; ERPL in December; liver protein carbonyl in March) with increasing levels of TOCAA. We also observed a TOCAA-stimulated increase in susceptibility of erythrocytes to peroxidative lysis in March at the highest levels of TOCAA. The data suggest that under most circumstances a progressive decrease in oxidative stress occurs as dietary TOCAA increases, but higher TOCAA concentrations can stimulate oxidative damage in some situations. Higher levels of TOCAA in the diet were required in March than in December to achieve comparable levels of protection against oxidative damage, which may have been due to physiological changes associated with the parr-smolt transformation. Erythrocytes appeared to be more sensitive to variation in dietary levels of TOCAA than liver and kidney tissues. Using the March ERPL assay results as a baseline, a TOCAA level of approximately 350-600 mg/kg diet would provide adequate protection against lipid peroxidation under most circumstances in juvenile Chinook salmon.

Seasonally Adjusting Ration Levels of Juvenile Hatchery Spring Chinook Salmon and Coho Salmon Does Not Alter Adult Survivals

AbstractThe feeding rate of juvenile spring Chinook salmon Oncorhynchus tshawytscha and coho salmon O. kisutch was substantially reduced in winter and substantially increased in spring in an attempt to increase postrelease survivals. All groups were coded‐wire‐tagged, and the experiment was replicated for 3 years. Although feed savings were sometimes realized, the results showed no significant difference in adult survival rates among hatchery returns, as determined by tag recoveries in fisheries, and spawning bed recoveries for the years examined.