Steelhead Research Articles

Duration in captivity affects competitive ability and breeding success of male but not female steelhead trout (Oncorhynchus mykiss)

Female steelhead trout (Oncorhynchus mykiss) reared for 1 year (traditional, “S1”) and 2 years (experimental, “S2”) in captivity in the Methow River Basin, Washington, produced very similar numbers of offspring in replicate spawning channels over 3 consecutive years. In contrast, S1 anadromous males outcompeted S2 males for access to nesting females and, as a result, produced significantly more offspring. Male dominance was positively associated with body mass, but body mass did not account for differences between S1 and S2 males. Much smaller precocious S2 males that matured during rearing in hatchery raceways sired offspring in all six breeding groups. Contributions from precocious males were nearly always the result of sneak spawning events, although on rare occasions, precocious males were able to stimulate females to spawn in the absence of an anadromous male. Similarities in female breeding success suggest that S1 and S2 hatchery steelhead should exhibit similar productivity under natural conditions, but S1 male steelhead may result in greater rates of gene flow from hatchery to natural populations.

Carcass Additions Influence Food Webs Through Bottom-Up and Direct Consumption Pathways Along a Fish Species Assemblage Gradient

The loss of subsidies delivered by anadromous fish to inland stream ecosystems may have profound influences on stream food webs. However, studies have focused on food web responses in ecosystems where the fish assemblage is dominated by salmonids. We evaluated food web responses to carcass additions in three locations of an interior Columbia River Basin stream with varying native fish assemblages. Periphyton biomass responses were mixed with increases in treatment compared to control reaches of the middle and downstream pairs, but not in the upstream pair where scavenging by bears removed the majority of carcasses. Stable isotope analysis revealed marine-derived nutrient (MDN) enrichment of periphyton and invertebrate functional feeding groups in the middle and downstream pairs (up to 12% MDN derived), but not in the upstream pair. Non-salmonid fish exhibited limited MDN assimilation (~ 5 and 10% MDN derived), with isotopic enrichment patterns similar to lower trophic levels and little evidence of eggs and carcass material consumption, suggesting bottom-up transfer of MDN to non-salmonid fishes. In contrast, across the three study pairs, juvenile Chinook Salmon (Oncorhynchus tshawytscha) and steelhead trout (O. mykiss) assimilated MDN rapidly, obtaining up to 25% and 57% of their nitrogen from carcasses, respectively. Diet analysis and isotopic enrichment patterns indicated that juvenile salmonid assimilation occurred primarily through direct consumption of eggs and carcass tissue. Our findings suggest that salmonids in this region may experience more benefit from carcass additions containing eggs, while non-salmonids are likely to experience minimal MDN incorporation whether or not eggs are present.

Environmental correlates of fine-scale juvenile steelhead trout (Oncorhynchus mykiss) habitat use and movement patterns in an intermittent estuary during drought

We used acoustic telemetry and environmental monitoring to elucidate preferred microhabitats of juvenile steelhead trout (Oncorhynchus mykiss) in a Central California intermittent estuary (IE) during historic drought. We collected over half a million fish locations in the Pescadero IE (San Mateo County, CA) across 15 weeks during an extended sandbar-closed period which permitted quantification of fine scale habitat use and movement patterns. Tagged juvenile steelhead expressed strong site fidelity, especially at night when core habitat area - defined as the 50% probability of being present in an area - contracted by over one order of magnitude. The rate of movement was slow overall (~0.4 to 0.6 lengths·s−1) and remained at baseline levels at night (~40 mm∙s−1). The daytime rate of movement generally tracked solar radiation levels and appeared to be moderated by water temperatures. Spikes in the rate of movement occurred during crepuscular periods and the maximum hourly rate of movement (138 mm∙s−1) was observed during the early study period from 10:00 to 11:00 when water temperatures were physiologically optimal (17–18 °C). Water quality worsened upstream when water temperatures exceeded 18 °C and dissolved oxygen concentrations declined below 7.0 mg·L−1. Fish tag detections at stationary receivers in the upper estuary declined linearly with deteriorating water quality conditions. Qualitative analysis of juvenile steelhead habitat utilization indicated a strong preference for two microhabitat features in the estuary during the study; both were shallow (~1.5 m), wind-protected, and possessed cover and sandy substrates that occurred within the fresh or near fresh epilimnion where lagoon water quality was best and benthic prey was likely most abundant. Upstream movement occurred in late fall for over half of the tagged cohort, which likely enhances population resiliency by allowing these fish to escape lethal water quality conditions coincident with the transition from closed to open estuary in late fall. Climate projections for California’s Central Coast predict an increase in extreme dry events and the information presented here can help natural resource managers prepare for the future, such as the critical need to promote development of a sufficiently oxygenated epilimnion during extended sandbar-closed ecosystem states.

Salmonid Habitat and Population Capacity Estimates for Steelhead Trout and Chinook Salmon Upstream of Scott Dam in the Eel River, California

Estimating salmonid habitat capacity upstream of a barrier can inform priorities for fisheries conservation. Scott Dam in California's Eel River is an impassable barrier for anadromous salmonids. With Federal dam relicensing underway, we demonstrated recolonization potential for upper Eel River salmonid populations by estimating the potential distribution (stream-km) and habitat capacity (numbers of parr and adults) for winter steelhead trout (Oncorhynchus mykiss) and fall Chinook salmon (O. tshawytscha) upstream of Scott Dam. Removal of Scott Dam would support salmonid recovery by increasing salmonid habitat stream-kms from 2 to 465 stream-km for steelhead trout and 920 to 1,071 stream-km for Chinook salmon in the upper mainstem Eel River population boundaries, whose downstream extents begin near Scott Dam and the confluence of South Fork Eel River, respectively. Upstream of Scott Dam, estimated steelhead trout habitat included up to 463 stream-kms for spawning and 291 stream-kms for summer rearing; estimated Chinook salmon habitat included up to 151 stream-kms for both spawning and rearing. The number of returning adult estimates based on historical count data (1938 to 1975) from the South Fork Eel River produced wide ranges for steelhead trout (3,241 to 26,391) and Chinook salmon (1,057 to 10,117). An approach that first estimated juvenile habitat capacity and then used subsequent life stage survival rates yielded 1,281 (CV 56%) steelhead trout and 4,593 (CV 34%) Chinook salmon returning adults. Variability in estimated fish numbers reflects application of densities and survival rates from other populations, assumptions about salmonid productivity in response to potential spawning habitat capacity, residency and outmigration of early life-stages, summertime water quality conditions, and inter-annual hydrograph, marine, and population variability.

Growth, osmoregulation and energy budget of rainbow and steelhead trout under different salinity acclimation methods and the best transition size of steelhead trout

In order to meet the demand of salmon market, Chinese scientists and entrepreneurs are working on salmon mariculture far offshore in the Yellow Sea, China. Rainbow, steelhead trout and Atlantic salmon were selected as the main culture species. The aims of the present study were as follows: (a) investigate the effect of the salinity acclimation method on the growth, osmoregulation and energy budget in two forms of Oncorhynchus mykiss, rainbow and steelhead trout and (b) explore the optimal size of steelhead trout for the seawater entry. In trial I, rainbow (mean = 99.44 g) and steelhead trout (mean = 99.01 g) were reared for 40 days after undergoing salinity acclimation at three rates: an abrupt increase in salinity from 0 to 30 g/L (T30); an abrupt increase in salinity to 14 g/L, followed by a daily increase of 2 g/L (T2) or 6 g/L (T6) until reaching 30 g/L; and no salinity exposure (control treatment) (T0). In trial II, steelhead trout with body weights of approximately 100 and 400 g were cultured for 60 days with two treatments, T0 and T2, and the specific growth rate (SGR) was calculated every 10 days. In trial I, in both kinds of fish, the optimal growth performance, survival rate, osmoregulation and energy budget were observed in the T0 treatment, followed by the T2 treatment. These results indicate that O. mykiss with a body weight of approximately 100 g can adapt to sea water with a gradual transition (T2), but they are still not suitable for the seawater entry because of low growth. Based on the recorded SGRs in trial II, our formulated regression formula revealed that approximately 200 g is the optimal size of steelhead trout for the transition to sea water.

Infectious hematopoietic necrosis virus specialization in a multihost salmonid system.

Many pathogens interact and evolve in communities where more than one host species is present, yet our understanding of host–pathogen specialization is mostly informed by laboratory studies with single species. Managing diseases in the wild, however, requires understanding how host–pathogen specialization affects hosts in diverse communities. Juvenile salmonid mortality in hatcheries caused by infectious hematopoietic necrosis virus (IHNV) has important implications for salmonid conservation programs. Here, we evaluate evidence for IHNV specialization on three salmonid hosts and assess how this influences intra‐ and interspecific transmission in hatchery‐reared salmonids. We expect that while more generalist viral lineages should pose an equal risk of infection across host types, viral specialization will increase intraspecific transmission. We used Bayesian models and data from 24 hatcheries in the Columbia River Basin to reconstruct the exposure history of hatcheries with two IHNV lineages, MD and UC, allowing us to estimate the probability of juvenile infection with these lineages in three salmonid host types. Our results show that lineage MD is specialized on steelhead trout and perhaps rainbow trout (both Oncorhynchus mykiss), whereas lineage UC displayed a generalist phenotype across steelhead trout, rainbow trout, and Chinook salmon. Furthermore, our results suggest the presence of specialist–generalist trade‐offs because, while lineage UC had moderate probabilities of infection across host types, lineage MD had a small probability of infection in its nonadapted host type, Chinook salmon. Thus, in addition to quantifying probabilities of infection of socially and economically important salmonid hosts with different IHNV lineages, our results provide insights into the trade‐offs that viral lineages incur in multihost communities. Our results suggest that knowledge of the specialist/generalist strategies of circulating viral lineages could be useful in salmonid conservation programs to control disease.

High Prevalence of the Copepod Salmincola californiensis in Steelhead Trout in Lake Ontario Following its Recent Invasion

Salmincola californiensis (Dana, 1853) (Subclass Copepoda: Family Lernaeopodidae) is known to parasitize salmonids of the genus Oncorhynchus including Oncorhynchus mykiss (rainbow trout), Oncorhynchus tshawytscha (chinook salmon), and Oncorhynchus kisutch (coho salmon). These 3 salmonids have been introduced to the Great Lakes intermittently since the mid-1800s. As we demonstrate here, the introduction of these salmonids to the Great Lakes was followed, at some point, by the introduction of their parasitic gill copepod, S. californiensis. Given anecdotal accounts of S. californiensis in introduced salmonids in Lake Ontario since 2012, we chose to conduct a survey to formally document the occurrence of this introduced species. Our survey took place during spring, summer, and fall of 2018 and during spring of 2019 at the south-eastern side of Lake Ontario. Prevalence of S. californiensis was 69, with a mean intensity of 2.7 in 61 rainbow trout examined in 2018. In 2019, prevalence of S. californiensis was 71, with a mean intensity of 3.6 in 59 rainbow trout examined. The prevalence of S. californiensis was 39, with a mean intensity of 1.6 in 223 chinook salmon examined in 2018. No specimens of S. californiensis were found in the 100 coho salmon examined in 2018. The prevalence of S. californiensis in rainbow trout is of great concern considering that it is double that found in rainbow trout in the native range (69 [in 2018] and 71 [in 2019] vs. 35). This is the first formal documentation of the invasion of S. californiensis in Lake Ontario. Future fisheries management decisions in Lake Ontario and its tributaries should take into account these data.

Does broodstock source affect post-release survival of steelhead? Implications of replacing a non-native hatchery stock for recovery

Steelhead trout (Oncorhynchus mykiss) reared at the Nimbus Fish Hatchery (NFH) and released into the Lower American River (LAR) in California are not part of the native California Central Valley Distinct Population Segment (CCVDPS); listed as threatened under the Endangered Species Act (ESA), and therefore cannot contribute to recovery. In response to this situation, we evaluated the potential of using a CCVDPS stock from the Coleman National Fish Hatchery (CNFH) to aid in recovery. Steelhead from the CNFH were reared in 2015 at NFH along with NFH-origin steelhead. Smolts from both stocks were implanted with acoustic transmitters and released into the LAR. This study assessed: 1) reach-specific, post-release survival of each stock from release to the ocean; 2) the degree to which either stock residualized; and 3) the spatial distribution of post-release mortality in the LAR. Multistate mark-recapture models were constructed to estimate reach-specific survival and entrainment into alternate migration routes. Four models were constructed to test hypothesized relationships between survival and covariates. Covariates included: 1) broodstock origin; 2) release date; 3) fork length; and 4) no covariates. Fork length was the best predictor of reach-specific survival and exhibited a positive relationship with survival in each reach. Juveniles from both stocks emigrated quickly, did not residualize, and exhibited similar survival while emigrating to the ocean. Results suggested the need for additional research to further evaluate CNFH-origin steelhead performance at NFH-origin during additional life stages to support recovery of CCVDPS Steelhead.

Partial migration alters population ecology and food chain length: evidence from a salmonid fish

AbstractMany migratory species, from monarch butterflies to wildebeest, express partial migration, where only a subset of a population migrates. This intraspecific variation is likely to have large ecological consequences. We studied the ecological consequences of partial migration in a salmonid fish, Oncorhynchus mykiss, in coastal streams in California, USA. One ecotype, steelhead trout, migrates to the ocean, whereas the other, rainbow trout, completes its lifecycle in freshwater. Migration has a strong genetic basis in O. mykiss. In one stream, we found differences in the frequency of migration‐linked genotypes below and above a waterfall barrier (migratory allele frequency of 60% below vs. 31% above). Below the waterfall, in the migratory‐dominated region, the density of young fish (<1 yr old) was approximately twice that in the resident‐dominated region above the waterfall (0.46 vs. 0.26 individuals/m2, respectively), presumably reflecting the higher fecundity of migratory females. Additionally, there were half as many older fish (>1 yr old) in pools downstream of the waterfall (0.05 vs. 0.13 individuals/m2). In a second stream, between‐year variation in the dominance of migratory vs. resident fish allowed us to explore differences in fish density and size structure through time, and we found a consistent pattern. In brief, when migratory genotypes dominated, we found higher densities of young fish and lower densities of older fish, resulting in a simpler size structure, compared to when resident genotypes dominated. Moreover, large resident trout had a slightly higher trophic position than young fish (3.92 vs. 3.42 in one creek and 3.77 vs. 3.17 in the other), quantified with stable isotope data. The difference in fish size structure did not generate trophic cascades. Partial migration is widespread among migratory populations, as is phenotypic divergence between resident and migratory forms, suggesting the potential for widespread ecological effects arising from this common form of intraspecific variation.

Growth, osmoregulatory response, adenine nucleotide contents, and liver transcriptome analysis of steelhead trout (Oncorhynchus mykiss) under different salinity acclimation methods

Chinese researchers have been working salmon mariculture far offshore in the Yellow sea, and steelhead trout is one of the popular Salmonidae. This study was conducted to investigate the effect of different salinity acclimation methods on the growth, osmoregulation, energy balance, and liver transcriptome of steelhead trout (Oncorhynchus mykiss). Fish (initial weight, 394.50 g) were reared for 40 days after undergoing salinity acclimation at three rates: an abrupt increase in salinity from zero to 30 ppt (T30); an abrupt increase in salinity to 14 ppt, followed by a daily increase of six ppt (T6) or two ppt (T2), until reaching 30 ppt; and no salinity exposure (control group, T0). Subsequently, serum was collected to determine osmolality, iron concentration, Na+-K+-ATP (NKA) and Ca2+-Mg2+-ATP (CMA) activity; muscle and gill samples were collected for the determination of adenosine 5′-triphosphate (ATP); liver transcriptome was compared between the T0 and T2 groups. The final weight, specific growth rate, food conversion efficiency, and the ATP content of fish in the T2 group were significantly higher than those in the other groups. However, the serum osmolality, serum ion concentration, and gill NKA and CMA activity in the T2 group was significantly lower than that in the T6 and T30 groups. A total of 53,679 unigenes were produced, and 1438 differently expressed genes were selected by DESeq. Among them, 587 genes were up-regulated, while 581 were down-regulated. These differential genes were mainly related to the function of metabolites and ions transportation, energy metabolism, signal transduction, immune responses, and structural assembly. The results indicate that steelhead trout with a weight of approximately 400 g is suitable for mariculture, and T2 was the best transition method for salinity acclimation.

Occurrences of Steelhead Trout (Oncorhynchus mykiss) in southern California, 1994-2018

Occurrences of Steelhead Trout (Oncorhynchus mykiss) in southern California, 1994-2018

Impacts of Small-Scale Water Conservation Practices on Summer Streamflow in the Navarro River Watershed, California

The Navarro River watershed in coastal Northern California provides critical habitat for coho salmon and steelhead trout, but low summer streamflow limits habitat quality due to poor hydrologic connectivity, warm water temperatures, and low dissolved oxygen. Strategies to improve salmonid habitat include managing agricultural irrigation and other water use to increase summer streamflow. One such strategy is adding water storage ponds and tanks to replace summer diversions from streams with winter diversions to fill storage. A monthly water budget was developed for the watershed to assess the potential for flow enhancement via such water conservation efforts. Results indicate that adding 12,335 m3 (10 acre-feet) of storage in key tributary sub-watersheds would increase summer streamflows by 0.8 to 1.1 L/s. That represents an up to 12 percent increase in summer streamflow during a moderate drought and up to 100 percent or greater increase during a severe drought. Adding sufficient water storage to eliminate all summer diversions could increase streamflow by up to 21 L/s in tributaries and up to 58 L/s in the mainstem Navarro River. Given the sensitivity of California salmonids to minor changes in summer streamflow, the calculated flow benefits of water conservation would significantly improve salmonid habitat.

Spatiotemporal patterns in trophic niche overlap among five salmonines in Lake Michigan, USA

Native lake trout (Salvelinus namaycush) and introduced Chinook salmon (Oncorhynchus tshawytscha), coho salmon (Oncorhynchus kisutch), steelhead (Oncorhynchus mykiss), and brown trout (Salmo trutta) are major predators in Lake Michigan’s complex ecosystem and collectively support a valuable recreational fishery, but declines in their primary prey, alewife (Alosa pseudoharengus), have raised ecological and management concerns about competition and prey allocation. We applied niche overlap analysis to evaluate competition among salmonine predators during rapid forage base change in Lake Michigan. δ13C and δ15N stable isotope ratios indicated that lake trout had a unique trophic niche from inclusion of offshore and benthic prey, with <29% lake-wide niche overlap with Chinook salmon, coho salmon, and steelhead. Brown trout had moderate overlap with other species (45%–91%), while Chinook salmon, coho salmon, and steelhead had high overlap (71%–98%). Regional differences in isotopic signatures highlighted the potential importance of subsystem differences in fish diets in large aquatic systems. The uniqueness of the lake trout niche, and broadness of brown trout and steelhead niches, suggest these species may be resilient to forage base changes. This study further demonstrates how niche overlap analysis can be applied to tease apart competitive interactions and their response to ecosystem change.

Residual stress detection of welded parts based on excitation vibration response

With the rapid development of the equipment industry, people pay more attention to the stress research of materials. However, there is no more suitable and effective method to detect the variation of residual stress. To find an efficient and useful method to analyze the residual stress of the welded parts, this article selects the Q235 component as the research object and produces a detection robot with the core of processing vibration signal and extracting signal data. In combination with the vibration signal extracted by the robot, we study the influence law of the residual stress of the material through numerical simulation and experimental verification. The detection of residual stress is related to the change in the number of taps of the robot and the increase or decrease in the number of taps of the robot. We used the vibration signal extracted by the robot and analyzed the orthogonal parameters of the high-frequency induction welding process parameters to obtain a set of the most unique process parameters: The tapping angle was 7° and the tapping frequency was 300 Hz. We also set up the robot to extract and analyze the vibration signal using four different hammerheads. The results show that the sub-resonance analysis results as the standard, the deviation of the steel head and the aluminum head hammer is about ±10, the result is more accurate, and the frequency of the nylon and plastic hammer is lower, because it is softer. When the hammer is struck, the contact time of the hammerhead with the workpiece is lengthened, so that a lower frequency can be excited.

Flow regimes in coastal California steelhead trout streams: Spatiotemporal patterns in magnitude, duration and timing

AbstractThe magnitude, timing and duration of precipitation events can vary considerably across spatial and temporal scales. In lotic ecosystems, such differences in precipitation patterns can strongly influence water availability, which in turn affects the population dynamics of stream biota. Connectivity flow thresholds were developed for the movement of juvenile steelhead trout using hydraulic modelling for 37 coastal California streams. Spatial patterns in magnitude, and spatiotemporal patterns in duration and timing of flows meeting threshold levels were analysed using long‐term flow gaging data. Flow thresholds for the movement of juvenile steelhead through riffle sites varied from 0.06 (San Luisito Creek, Elder Creek) to 0.82 (Redwood Creek) cms (cubic meters per second). Flow thresholds increased positively with mean bankfull width, indicating that more water is required for fish movement in wider streams. Precipitation was a dominant driver of flow duration, with flows meeting thresholds longer in wetter regions of the state when compared with drier regions. On the rising limb of the hydrograph, the onset of meeting flow thresholds was influenced by stream width, with thresholds being met earlier in wider streams when compared with narrower streams. On the receding limb of the hydrograph, flow threshold timing was influenced by precipitation, with flows remaining above the threshold later in wetter regions when compared with drier regions. Based on these findings, we recommend that the management of aquatic resources for a broad range of objectives consider regional scales that account for local patterns in precipitation, channel form and prevailing water year conditions to accommodate California's wide spatiotemporal diversity of water availability.

Genetic Differentiation and Origin of Naturalized Rainbow Trout Populations From Southern Chile, Revealed by the mtDNA Control Region Marker.

Numerous self-sustaining naturalized or introduced populations of rainbow trout (Oncorhynchus mykiss) are widely distributed throughout the freshwaters of southern Chile. In this study, analysis of the mitochondrial DNA control region (CR) marker was conducted to investigate the level of genetic divergence among populations and their phylogenetic relationships with respect to native lineages. This information provided a framework to interpret the genetic structure and origin that was shaped during historical trout introduction efforts. To this end, we analyzed eleven naturalized populations of lakes and rivers from five basins. The CR marker revealed five haplotypes. The overall haplotype (H) and nucleotide (Π) diversities were 0.684 ± 0.030 and 0.00460 ± 0.00012, respectively. Global F ST was 0.169, with several pairwise F ST estimates showing significant differences (P < 0.05). The exact test of population differentiation corroborated this result (P < 0.001). Significant geographic structure was found (P < 0.05), with variations explained primarily by differences within populations (61.65%) and among group basins (20.82%). Maximum likelihood phylogenetic analysis resolved two distinct clades with medium bootstrap support when naturalized populations were aligned in conjunction with reference native lineages. The haplotype network revealed a close association between naturalized populations and four main haplotypes representative of three native ecotypes or lineages from western North America (rainbow trout, steelhead trout and redband trout). These results indicate a genetic population structuring for naturalized rainbow trout from southern Chile and an origin probably represented by multiple lineages sources. Thus, mitochondrial DNA data strongly suggest that stocking of rainbow trout from different origins may have occurred during or after the initial introduction efforts.

Temporal and Volumetric Characteristics of Lagoons in the Santa Monica Bay and the Passage Implications for Southern Steelhead Trout

Record drought from 2012 to 2016 followed by rainfall in the winter of 2017 provided an opportunity to examine how changing climate conditions may affect migration opportunities for the endangered southern steelhead trout (Oncorhynchus mykiss). This study examined how intermittently open estuary-ocean interfaces in the Santa Monica Bay that have historically supported steelhead evolved temporally and volumetrically. All seven lagoons in the study area breached by January 2017 after five years of drought and nearly exclusively closed conditions. Duration of breach was affected by the size of the lagoon, with smaller lagoons remaining breached longer than larger lagoons. Conversely, volume capacity persisted longer in larger lagoons. Lagoon condition was quantified by presence/absence of breach and passibility, coupled with daily rainfall. This study provides important lagoon planning, restoration and management information needed to support recovery of southern steelhead trout populations in the face of climate change.

Evaluation of effluent waste water from salmonid culture as a potential food and water supply for culturing larval Pacific lamprey Entosphenus tridentatus

The Pacific lamprey is an iconic native fish of great importance to the ecosystem and indigenous cultures in the U.S. Pacific Northwest. Pacific lamprey populations have declined in abundance from historic levels, and conservation aquaculture has been proposed as a technique to restore these populations. The present research focused on expanding the culture methods for larval lamprey. The larvae filter feed and cohabitate with juvenile salmonids in the wild, therefore the effluent water from rearing salmonids may be a viable source of water and food for culturing lamprey. This approach could be a sustainable method for raising lamprey at existing salmonid hatcheries. A nine week trial investigated the effects of rearing in effluent water from salmonid culture on the growth, survival, proximate composition, and fatty acid profile of larval lamprey. This trial also explored the potential of this rearing strategy to improve the water quality by removing nutrients from the effluent. The trial included three treatments testing the use of the effluent from steelhead trout (Oncorhynchus mykiss), a conventional lamprey diet (control diet), or both combined as a means for rearing lamprey. A fourth treatment where lamprey were excluded served as a water quality control to test the effect of lamprey presence on effluent quality. Lamprey survival was not affected by treatment. Lamprey reared solely on the effluent waste matched the survival and growth of fish fed the conventional diet. Lamprey fed the combination treatment grew faster than the conventional diet fed fish. Whole body lipid levels were elevated in lamprey from the combination treatment relative to the conventional diet fed lamprey. Crude protein in the whole bodies of effluent fed lamprey was low compared to fish from either of the treatments where the conventional diet was fed. Lamprey offered the effluent nutrients were high in saturated fats relative to the control fed fish, which reflected the lipid profile of this diet. However, lamprey from the combination treatment were lower in long chain polyunsaturated fatty acids relative to the control or the effluent treatment lamprey. There was no measureable improvement in water quality due to the presence of lamprey, though lamprey were able to sequester approximately 1.3% of the effluent dry matter as lamprey biomass. Overall, it appears the larval stage of lamprey can be effectively reared on salmonid effluent, and this method provides superior growth when used in combination with a conventional lamprey diet.

Carcass additions increase juvenile salmonid growth, condition, and size in an interior Columbia River Basin tributary

Numbers of anadromous fish returning to freshwater ecosystems have declined precipitously across much of western North America, reducing a potentially important resource subsidy for juvenile salmonids. We added carcasses to three sections of a Snake River tributary and assessed juvenile Chinook salmon (Oncorhynchus tshawytcha) and steelhead trout (Oncorhynchus mykiss) growth, body condition, size, and diet responses in summer and early fall. Juvenile salmonids consumed an abundance of eggs and carcass tissue, which increased energy rations. Within 3 weeks of carcass additions, juvenile Chinook and steelhead growth rates were 1.1–5 and 6–23 times greater in treatment reaches relative to control reaches, respectively. We used long-term tagging and detection data from this system to assess the relationship between juvenile Chinook size and emigration survival for two different juvenile life histories. The increased growth rates and body size in response to carcass additions, coupled with a positive relationship between body size and survival, suggest that juvenile salmonid rearing productivity and emigration survival may be limited by depressed returns of anadromous fishes in this system and potentially other tributaries of the Columbia Basin.

Hypoxic acclimation negatively impacts the contractility of steelhead trout (Oncorhynchus mykiss) spongy myocardium.

Cardiac stroke volume (SV) is compromised in Atlantic cod and rainbow trout following acclimation to hypoxia (i.e., 40% air saturation; ~8 kPa O2) at 10-12°C, and this is not due to changes in heart morphometrics or maximum achievable in vitro end-diastolic volume. To examine if this diminished SV may be related to compromised myocardial contractility, we used the work-loop method to measure work and power in spongy myocardial strips from normoxic- and hypoxic-acclimated steelhead trout when exposed to decreasing Po2 levels (21 to 1.5 kPa) at several frequencies (30-90 contractions/min) at 14°C (their acclimation temperature). Work required to lengthen the muscle, as during filling of the heart, was strongly frequency dependent (i.e., increased with contraction rate) but was not affected by hypoxic acclimation or test Po2. In contrast, although shortening work was less frequency dependent, this parameter and network (and power) 1) were consistently lower (by ~30-50 and ~15%, respectively) in strips from hypoxic-acclimated fish and 2) fell by ~40-50% in both groups from 20 to 1.5 kPa Po2, despite the already-reduced myocardial performance in the hypoxic-acclimated group. In addition, strips from hypoxic-acclimated trout showed a poorer recovery of net power (by ~15%) when returned to normoxia. These results strongly suggest that hypoxic acclimation reduces myocardial contractility, and in turn, may limit SV (possibly by increasing end-systolic volume), but that this diminished performance does not improve the capacity to maintain myocardial performance under oxygen limiting conditions.