Hatchery-reared Steelhead Research Articles

Thiamine Supplementation Improves Survival and Body Condition of Hatchery-Reared Steelhead (Oncorhynchus mykiss) in Oregon.

Early rearing of steelhead (Oncorhynchus mykiss) in Oregon hatcheries is often problematic; fry can become emaciated and die during the period between hatch and first feed. Thiamine (vitamin B1) deficiency has caused early mortality in salmonids; however, the thiamine status of Oregon's steelhead populations is unknown, to date. Of the 26 egg samples from three Oregon hatcheries in 2019, 20 (77%) had thiamine levels < 10 nmol/g, and 13 of those samples (50%) had levels <6.5 nmol/g, suggesting the thiamine deficiency of adult, female steelhead. To investigate if thiamine deficiency was causally related to fry survival, females were injected with buffered thiamine HCl 50 mg/kg prior to spawning; additionally, a subset of eggs were supplemented via bath treatment with thiamine mononitrate (1000 ppm) at spawning. Cumulative fry mortality at 8 weeks post-hatch from thiamine-injected females was 2.9% compared to 13.8% mortality of fry without thiamine supplementation. Fry treated only with the thiamine via bath as eggs had a mortality rate of 6.9%. There were no additional improvements for the survival of fry from injected females that also received a thiamine bath. Furthermore, condition factors were greater in thiamine-supplemented fry than in those that received no thiamine. These data identify thiamine deficiency in Oregon steelhead and suggest supplementation with thiamine can mitigate early rearing mortality.

Gut Microbial Composition of Pacific Salmonids Differs across Oregon River Basins and Hatchery Ancestry.

The gut microbiome may represent a relatively untapped resource in the effort to manage and conserve threatened or endangered fish populations, including wild and hatchery-reared Pacific salmonids. To clarify this potential, we defined how steelhead trout gut microbiome composition varies across watersheds and as a function of ancestry. First, we measured this variation across watersheds using wild steelhead trout sampled from nine locations spanning three river basins. While gut microbial composition differs across basins, there exist bacterial clades that are ubiquitous across all populations. Correlating the phylogenetic composition of clades with geographic distance reveals 395 clades of bacteria whose ecological distribution implicates their co-diversification with steelheads. Second, we quantified how microbiome composition varies between first generation hatchery-reared steelhead and traditional hatchery-reared steelhead. Despite being subject to the same hatchery management strategies, fish bred from wild parents carry distinct microbiomes from those bred from hatchery broodstock, implicating the role of genotype on microbiome composition. Finally, we integrated all data from both studies to reveal two distinct, yet robust clusters of community composition. Collectively, our study documents for the first time how the steelhead gut microbiome varies by geography or broodstock and uncovers microbial taxa that may indicate the watershed or hatchery from which an individual was sourced.

Family influence on length at release and size-biased survival post release in hatchery-reared steelhead: A mechanism to explain how genetic adaptation to captivity occurs

Genetic adaptation to captivity influences the reproductive success of hatchery-reared steelhead (Oncorhynchus mykiss) spawning in the wild, but the mechanism by which adaptation occurs is not well understood. Because body size-at-release is positively correlated with post-release survival in hatchery-reared smolts, one hypothesis is that hatcheries select for physiological and/or behavioral traits that promote fast growth in captivity. If those juvenile growth traits are maladaptive for spawning or offspring survival in the wild, then that could explain why hatchery fish quickly evolve to have lower reproductive success than natural-origin fish in the wild environment. First-generation hatchery-reared steelhead from the Hood River, (Oregon) have lower reproductive success in the wild than do natural-origin fish, and substantial evidence suggests the fitness difference is genetically based and due to genetic adaptation to captivity. Here we ask whether the ‘selection on size-at-release’ hypothesis could explain the rapid genetic adaptation observed in this well-studied steelhead population. Using scale analysis, we back-calculated length at ocean entrance to test whether size-selective survival occurred in two cohorts (brood year [BY] 1997 and 2009). In BY 2009, we found evidence of weak size-selective survival (difference of 9 mm between pre-release average length and back-calculated length from surviving adults), but in BY 1997, strong (37 mm difference) size-selective survival was observed. Family identity explained 33% of the variance in fork length before release, and fork length was highly heritable in both BY cohorts. Thus, the requisite genetic variation for response to selection on size-at-release exists in this population. Our results support the hypothesis that size-selective survival does occur after release, and that selection for traits promoting fast growth in the hatchery could be a mechanism by which rapid adaptation to captivity has occurred in the Hood River winter steelhead hatchery program.

Spawn date explains variation in growth rate among families of hatchery reared Hood River steelhead (Oncorhynchus mykiss)

Body size at release for hatchery-reared steelhead is positively correlated with probability of survival to return as an adult. Although the relationship between body size and survival is well documented, little is known about what factors influence growth in the hatchery at the family level. We test if parent length, parent type (hatchery or natural), parent run date, or date of spawning correlate with among-family variation in offspring growth in the hatchery. Using Hood River winter steelhead (Oncorhynchus mykiss), two experiments were performed over two brood years. No effect of father length, parental type, or parental run date was found on offspring length in either year. Mother length was positively correlated with offspring length during both brood years and egg size data suggest this result occurs because longer females have larger eggs (i.e., it is a maternal effect). Although run date of parents was not correlated with offspring size, the date of spawning was negatively correlated with offspring size in a year with a protracted spawning season. Families spawned later in the season were smaller than those spawned earlier even though all fish began feeding on the same date. The spawn date effect lasted surprisingly long, being correlated with offspring size one year after spawning. A possible explanation for the spawn date effect is that eggs from early-spawned families were reared in chilled water to slow development so all families would begin feeding on the same date (a common hatchery practice). Colder water could have reduced metabolic costs and provided a surplus of energy to be used for somatic growth. This study highlights a little-studied environmental effect that could have large effects on long-term growth rates for hatchery-reared O. mykiss.

The effects of high rearing density on the potential for domestication selection in hatchery culture of steelhead (Oncorhynchus mykiss)

Hatchery-reared steelhead (Oncorhynchus mykiss) often have lower fitness than natural-origin fish when spawning in the wild. Fitness loss in hatcheries is partly due to genetic adaptation to captivity (domestication), but the underlying selection pressures driving adaptation remain unknown. Circumstantial evidence suggests that adaptation to hatcheries is accelerated when fish are reared at high density. We hypothesized two mechanisms by which high rearing densities could accelerate adaptation to the hatchery. First, high density could increase the among-family component of variation in fork length, which could increase the opportunity for selection after release. Second, a growth trade-off in fork length among families could occur across densities (family-by-environment interaction). We raised the same set of families, in replicate, at each of two densities. We found main effects of density (high density reduced body size) and family (accounted for 33%–53% of variance in size at release) on juvenile fork length. However, high density did not increase the percentage of variance in fork length among families, and there was weak evidence for a family-by-environment interaction. We propose an alternate model of how increased density might exacerbate domestication selection. The relationship between size at release and probability of survival is strongly nonlinear (almost truncational) for steelhead. Because high density decreases the fork lengths of all families approximately equally, high density could simply reduce the number of families that are above a threshold for high survival, resulting in strong among-family selection after release from the hatchery.

Marine survival difference between wild and hatchery-reared steelhead trout determined during early downstream migration

We observed large survival differences between wild and hatchery-reared steelhead trout (Oncorhynchus mykiss) during the juvenile downstream migration immediately after release, which persisted through adult life. Following a railway spill of sodium hydroxide into the Cheakamus River, British Columbia, a short-term conservation hatchery rearing program was implemented for steelhead. We used acoustic telemetry and mark–recapture models to estimate survival of wild and (or) hatchery-reared steelhead during 4 years of the smolt migration, with both groups released in 2008. After adjusting for estimated freshwater residualization, 7%–13% of wild smolts and 30%–40% of hatchery smolts died in the first 3 km of the migration. Estimated survival from release to ocean entry was 71%–84% for wild fish and 26%–40% for hatchery fish and to exit from the Strait of Georgia system was 22%–33% for wild fish and 3.5%–6.7% for hatchery fish. A calculated 2.3-fold survival difference established during the downstream migration was similar to that after the return of adult spawners, as return rates were 8.0% for wild fish and 4.1% for hatchery fish. Contrary to current understanding, a large proportion of salmon mortality in the smolt-to-adult period, commonly termed “marine mortality”, may actually occur prior to ocean entry.

Differences in Lateral Line Morphology between Hatchery- and Wild-Origin Steelhead

Despite identification of multiple factors mediating salmon survival, significant disparities in survival-to-adulthood among hatchery- versus wild-origin juveniles persist. In the present report, we explore the hypothesis that hatchery-reared juveniles might exhibit morphological defects in vulnerable mechanosensory systems prior to release from the hatchery, potentiating reduced survival after release. Juvenile steelhead (Oncorhynchus mykiss) from two different hatcheries were compared to wild-origin juveniles on several morphological traits including lateral line structure, otolith composition (a proxy for auditory function), and brain weight. Wild juveniles were found to possess significantly more superficial lateral line neuromasts than hatchery-reared juveniles, although the number of hair cells within individual neuromasts was not significantly different across groups. Wild juveniles were also found to possess primarily normal, aragonite-containing otoliths, while hatchery-reared juveniles possessed a high proportion of crystallized (vaterite) otoliths. Finally, wild juveniles were found to have significantly larger brains than hatchery-reared juveniles. These differences together predict reduced sensitivity to biologically important hydrodynamic and acoustic signals from natural biotic (predator, prey, conspecific) and abiotic (turbulent flow, current) sources among hatchery-reared steelhead, in turn predicting reduced survival fitness after release. Physiological and behavioral studies are required to establish the functional significance of these morphological differences.

Variation in the Early Marine Survival and Behavior of Natural and Hatchery-Reared Hood Canal Steelhead

BackgroundHatchery-induced selection and direct effects of the culture environment can both cause captively bred fish populations to survive at low rates and behave unnaturally in the wild. New approaches to fish rearing in conservation hatcheries seek to reduce hatchery-induced selection, maintain genetic resources, and improve the survival of released fish.Methodology/Principal FindingsThis study used acoustic telemetry to compare three years of early marine survival estimates for two wild steelhead populations to survival of two populations raised at two different conservation hatcheries located within the Hood Canal watershed. Steelhead smolts from one conservation hatchery survived with probabilities similar to the two wild populations (freshwater: 95.8–96.9%, early marine: 10.0–15.9%), while smolts from the other conservation hatchery exhibited reduced freshwater and early marine survival (freshwater: 50.2–58.7%, early marine: 2.6–5.1%). Freshwater and marine travel rates did not differ significantly between wild and hatchery individuals from the same stock, though hatchery smolts did display reduced migration ranges within Hood Canal. Between-hatchery differences in rearing density and vessel geometry likely affected survival and behavior after release and contributed to greater variation between hatcheries than between wild populations.Conclusions/SignificanceOur results suggest that hatchery-reared smolts can achieve early marine survival rates similar to wild smolt survival rates, and that migration performance of hatchery-reared steelhead can vary substantially depending on the environmental conditions and practices employed during captivity.

Development of natural growth regimes for hatchery-reared steelhead to reduce residualism, fitness loss, and negative ecological interactions

Wild steelhead (Oncorhynchus mykiss) typically spend two or more years in freshwater before migrating to sea, but hatchery steelhead are almost ubiquitously released as yearlings. Their large size at release coupled with life history pathways that include both male and female maturation in freshwater present ecological risks different from those posed by hatchery populations of Pacific salmon. Yearling hatchery reared steelhead that fail to attain minimum thresholds for smoltification or exceed thresholds for male maturation tend to ‘residualize’ (i.e., remain in freshwater). Residuals pose ecological risks including size-biased interference competition and predation on juvenile salmon and trout. Three hatchery populations of steelhead in Hood Canal, WA were reared under growth regimes designed to produce a more natural age at smoltification (age-2) to aid in rebuilding their respective natural populations. Mean smolt sizes and size variability at age-2 were within the range of wild smolts for two of the three populations. The third population reared at a different facility under similar temperatures exhibited high growth rate variability and high male maturation rates (20% of all released fish). Experimentally comparing age-1 and age-2 smolt programs will help identify optimal rearing strategies to reduce the genetic risk of domestication selection and reduce residualism rates and associated negative ecological effects on natural populations. Investigations of Winthrop National Fish Hatchery summer-run steelhead will measure a) selection on correlated behavioral traits (‘behavioral syndromes’), b) degree of smoltification, c) changes in hormones that regulate gonad growth at key developmental stages, and d) conduct extensive post-release monitoring of fish reared under each growth regime.

Seasonal foraging and piscivory by sympatric wild and hatchery-reared steelhead from an integrated hatchery program

We compared the diet of hatchery-reared steelhead produced from an integrated hatchery program as emigrating spring smolts and non-migrating hatchery residuals to their sympatric wild counterparts. Our results suggest that there is a potential for hatchery fish to affect wild steelhead populations due to dietary overlap and subyearling salmonid predation; however, relative ecological risk did not increase as steelhead delayed or forwent emigration. Predation by hatchery smolts was related to release timing, but not experience with native fish. Diet composition appears to be more strongly affected by seasonal and yearly differences in prey abundance and presence rather than differences in rearing environments. Hatchery and wild steelhead showed small but important foraging differences. Hatchery smolts did not consume as many salmonids as wild fish and hatchery residuals showed relatively stronger surface oriented feeding behavior than wild parr. Because most hatchery smolts emigrated shortly after release and the overall number of residuals in the study creek was low, we speculate that in this case there is low dietary and predatory-based risk of hatchery steelhead in Abernathy Creek negatively impacting wild salmonids.

Upstream Movement of Residual Hatchery Steelhead into Areas Containing Bull Trout and Cutthroat Trout

Hatchery-reared steelhead Oncorhynchus mykiss that do not emigrate as smolts shortly after release may harm wild fish communities through ecological interactions. We used systematic, stratified snorkeling surveys to document the relative abundance of wild rainbow trout (nonanadromous O. mykiss), bull trout Salvelinus confluentus, and westslope cutthroat trout O. clarki lewisi as well as the upstream limit of residual hatchery steelhead (hatchery-reared steelhead that had failed to emigrate by June 1). Our objective was to determine whether residual hatchery steelhead had migrated upstream from their release point into an area containing westslope cutthroat trout and a threatened population of bull trout. Hatchery steelhead made up a larger proportion of the salmonid community in the sites near their release location and constituted a lower proportion as distance upstream from the release location increased. However, residual hatchery steelhead had migrated over 12 km upstream into an area containing westslope cutthroat trout and a threatened stock of bull trout.

Effect of Smolt Length at Release on Adult Returns of Hatchery-Reared Winter Steelhead

Abstract Smolts of hatchery-reared steelhead Oncorhynchus mykiss were tagged by length-group and released in 1983 and 1984 on the Cowlitz River, Washington. Recovery of adults was significantly greater for smolts 190 mm and larger compared with returns of smaller fish.

Effects of Residual Hatchery-Reared Steelhead on Growth of Wild Rainbow Trout and Spring Chinook Salmon

Abstract We investigated the effects of nonmigrant (residual) juvenile hatchery steelhead (anadromous rainbow trout Oncorhynchus mykiss) on growth of wild rainbow trout and juvenile spring Chinook salmon O. tshawytscha to examine how increased densities of residual hatchery steelhead might affect the growth of preexisting wild rainbow trout and Chinook salmon. We used screened enclosures in a natural stream to examine food utilization and physiological stress, factors that might affect fish growth. The presence of residual hatchery steelhead led to reduced growth of wild rainbow trout (1993: P = 0.019; 1994: P = 0.020) but not of spring Chinook salmon (P = 0.360). Enclosures did not reduce the total number of food items available but did influence the species composition of aquatic and terrestrial invertebrates. The food habits of paired and unpaired fish differed; however, the power of those tests was low. Cortisol level, a measure of physiological stress, did not differ between paired and unpaired fish ...

Reducing Feed Levels during the Last Month of Rearing Enhances Emigration Rates of Hatchery-Reared Steelhead Smolts

Abstract Downstream migration of hatchery-raised smolts of steelhead Oncorhynchus mykiss maintained on a reduced-feed diet during the last month of rearing was compared with migration of fish fed to satiation (control diet) before release. Five releases were made in two streams over 3 years. Fish on the reduced diet averaged 7 mm shorter and 21 g lighter than control fish at release and had an average condition factor (K = 105 [weight,g]/[length,mm]3) of 0.92, versus 1.03 for control fish. An average of 57.5% of reduced-diet fish were recaptured, compared with 49.4% recapture of control fish; recoveries favored the test group for each release, and the difference was significant for three releases. Fish on the reduced diet generally arrived at traps 1–2 d sooner than control fish. Savings in fish feed costs were also realized with the reduced diet strategy.

The effects of hatchery and wild ancestry and experience on the relative ability of steelhead trout fry (Oncorhynchus mykiss) to avoid a benthic predator

Differences in selection regimes between hatchery and natural environments and environmental stimuli, among other factors, have the potential to cause differences in predator avoidance ability between hatchery and wild steelhead trout fry (Oncorhynchus mykiss). In two separate laboratory experiments, fry raised from eggs of wild Quinault River steelhead trout survived predation by prickly sculpin (Cottus asper) significantly better than size-matched offspring of a locally derived hatchery population, which were reared under similar conditions. Wild fry also survived predation better than hatchery fry in natural stream enclosures over a 3-day test period. Experience, in the form of 50-min visual exposure to sculpin predation on "sacrificial" steelhead trout, improved the ability of fry from both populations to avoid predation by sculpin. Wild-experienced fry were eaten in the fewest number of trials followed by wild-naive, hatchery-experienced, and hatchery-naive fry. The results of this study are consistent with the hypothesis that innate predator avoidance ability has been negatively altered through domestication and that attempts to condition hatchery-reared steelhead to avoid predators may be limited for domesticated populations.

A Method to Reduce the Abundance of Residual Hatchery Steelhead in Rivers

Abstract We developed and tested a release strategy designed to reduce the number of hatchery-reared steelhead Oncorhynchus mykiss that fail to migrate out of the Tucannon River (i.e., residualize) in southeast Washington. We also described the physical characteristics of those fish that failed to emigrate. Hatchery-reared steelhead that residualize may have negative effects on naturally produced salmonids through competition for food and space, predation, and the spread of disease. Steelhead residualism was reduced by retaining fish in the Curl Lake acclimation pond after volitional emigration had ceased. Fish that remained in the pond had a male : female ratio of 4: 1; 90% of these fish were a combination of transitional, parr, and precocious male stages. This method resulted in 2,022 residualized fish in the Tucannon River, 3.l% of the fish planted in Curl Lake. During the same year, 4,186 fish (14.0% of fish released) residualized in the Tucannon River from a direct river release. The 3.1 % residualis...

Riverine Predation on Sockeye Salmon Fry Migrating to Lake Washington

Abstract Recent declines in freshwater survival of juvenile sockeye salmon Oncorhynchus nerka in Lake Washington, Washington, prompted an examination of stage-specific mortalities. Previous investigations obscured the effects of winter flooding and postemergent predation on estimates of egg-to-fry survival. The purpose of this study was to explicitly estimate predation losses so that biotic and abiotic sources of mortality could be identified and quantified. During 1983–1985, the smolts of wild steelhead O. mykiss were the primary riverine predator of sockeye salmon fry migrating from the Cedar River into Lake Washington. Fry constituted 2–52% wet biornass of the smolts' diet, and averaged 13% of the diet from February through mid-May. Hatchery-reared steelhead smolts were stocked in the river during the latter half of the fry migration but showed no evidence of preying on fry. Fifty-four bioenergetics simulations were run to examine the effects of different rates of predator growth, temperature regimes, ...

Smolting of Hatchery-Reared Steelhead Transferred as Eyed Eggs from the Northern to the Southern Hemisphere

Abstract The effects of a Northern-to-Southern Hemisphere shift on the growth and smolting of steelhead (Oncorhynchus mykiss) were monitored by reference to physiological criteria. Eyed eggs were imported from the Alsea River Trout Hatchery, Oregon, USA (latitude 44°N), to the Lake Rupanco Experimental Hatchery in Chile (latitude 41°S). This transfer of eggs resulted in a notable variation in the age and size at which fish smolted. A minimum smolting size of about 10 cm was observed in the first southern spring of life, when fish were 7–8 months old. Fish that did not reach this size smolted in the second spring of life at age 20 months. Based on our current understanding of the effects of environmental variations on smolt physiology, we offer guidelines for increasing the efficiency of smolt production for this anadromous salmonid in the Southern Hemisphere.

Effects of baffles and isolation on dorsal fin erosion in steelhead trout, Oncorhynchus mykiss (Walbaum)

Abstract. Dorsal fin condition was evaluated in two groups of hatchery-reared steelhead trout, Oncorhynchus mykiss(Walbaum), and compared to wild fish. Hatchery fish were reared either in nursery tanks with baffles or in isolation (1 fish/rearing space). Evaluations were conducted to determine differences in dorsal fin condition between these groups and to monitor the progression and severity of fin damage. Isolated hatchery and wild steelhead trout maintained perfect dorsal fins with characteristic white margins. Hatchery fish reared in nursery tanks with baffles experienced dorsal fin erosion that started when the fish were about 40mm total length (30 days after being on feed). This erosion continued until dorsal fin length averaged only 2·3 mm in fish 161–200 mm total length in contrast to an average dorsal fin length of 20·9mm in wild fish of the same size.

Returns of Pen-Reared Steelhead from Riverine, Estuarine, and Marine Releases

Hatchery-reared steelhead (anadromous rainbow trout Oncorhynchus mykiss) were released as smolts in 1982 and 1983 at four locations in and near the Keogh River on northern Vancouver Island, British Columbia, to determine the effect of release location on adult return rate, Smolts were released at four sites simultaneously: 10 km upstream from the river mouth (10km site), 0.4 km upstream from the river mouth above a fish-counting fence (0.4-km site), in the tidal area below the fence (0.3 km upstream), and in the ocean about 1.6 km off the mouth of the river. Return rates were estimated by mark and recapture of adults and kelts at the counting fence 1–3 years later. Based on numbers released, the return rates of the 1982 groups were 7% for the 10-km site, 11% for the 0.4-km site, 10% for the tidal site, and 11% for the ocean site, The respective return rates of the 1983 groups were 3, 5, 7, and 5%. We suggest that failure to migrate, as well as predation, accounted for the lower return rates offish released at the 10-km site because few of the nonmigrant fish released at this site were collected at the fence as smolts the next year. Smolts that were acclimatized to salt water at the river mouth and then released at the ocean site returned at a rate similar to that of fish released into the lower reach of the river (0.3- and 0.4km sites). Release of cultured smolts into the lower reaches of small coastal rivers is therefore recommended to maximize adult survival and to minimize competition with wild steelhead.