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At least 649 records · Page 36Linked to original sources

USGS2011

A nematomorph parasite explains variation in terrestrial subsidies to trout streams in Japan

Nematomorph parasites alter the behavior of their orthopteran hosts, driving them to water and creating a source of food for stream salmonids. We investigated whether nematomorphs could explain variation in terrestrial subsidies across several streams. In nine study streams, orthopterans comprise much of the stomach contents of trout (46 ± 31% on average). Total mass of ingested prey per trout biomass positively correlated with the mass of orthopterans ingested, suggesting that the orthopterans enhanced absolute mass of prey consumption by the trout population. The orthopterans ingested per trout biomass positively correlated with the abundance of nematomorphs in the stream, but not with the abundance of camel crickets (the dominant hosts) around the streams. Streams in conifer plantations had fewer nematomorphs than streams in natural deciduous forests. These results provide the first quantitative evidence that a manipulative parasite can explain variation in the allochthonous energy flow through and across ecosystems.

Oikos↗

USGS2019

Variable hybridization outcomes in trout are predicted by historical fish stocking and environmental context

Hybridization can profoundly affect the genomic composition and phenotypes of closely related species, and provides an opportunity to identify mechanisms that maintain reproductive isolation between species. Recent evidence suggests that hybridization outcomes within a species pair can vary across locations. However, we still don’t know how extensive variation in outcomes of hybridization is across geographic replicates, and what mechanisms drive that variation. In this study, we described hybridization outcomes across 27 locations in the North Fork Shoshone River basin (Wyoming, USA) where native Yellowstone cutthroat trout and introduced rainbow trout co-occur. We used genomic data and hierarchical Bayesian models to precisely identify ancestry of hybrid individuals. Hybridization outcomes varied across locations. In some locations, only rainbow trout and advanced backcrossed hybrids towards rainbow trout were present, while other locations had a broader range of ancestry, including both parental species and first-generation hybrids. Using an individual-based simulation, we found that outcomes of hybridization in the North Fork Shoshone River basin deviate substantially from what we would expect under assumptions of random mating and no selection against hybrids. Since this implies that some mechanisms of reproductive isolation function to maintain parental taxa and a diversity of hybrid types, we then modeled hybridization outcomes as a function of environmental variables and stocking history that are likely to affect prezygotic barriers to hybridization. Variables associated with history of fish stocking were the strongest predictors of hybridization outcomes, followed by environmental variables that might affect overlap in spawning time and location.

Wyoming↗

USGS2021

Carcass deposition to suppress invasive lake trout causes differential mortality of two common benthic invertebrates in Yellowstone Lake

Invasive species require management to mitigate their harmful effects on native biodiversity and ecosystem processes. However, such management can also have negative, unintended consequences on non-target taxa, ecosystem processes, and food web dynamics. In Yellowstone Lake, invasive lake trout ( Salvelinus namaycush ) have caused a decline in the native Yellowstone cutthroat trout ( Oncorhynchus clarkii bouvieri ) population. To suppress the invader, lake trout carcasses are deposited on the species’ spawning sites, causing embryo mortality by reducing dissolved oxygen as they decay. The non-target effects of carcass treatment are unknown, but benthic invertebrates may be sensitive to reductions in dissolved oxygen. Benthic invertebrate taxa have varying hypoxia tolerances; caddisflies ( Trichoptera , family Limnephilidae ) are hypoxia sensitive while amphipods Gammarus lacustris and Hyallela azteca are hypoxia tolerant. Both are widespread and abundant in Yellowstone Lake and comprise a large proportion of fish diets, so changes in their abundances could alter food web dynamics. We conducted an in situ experiment to determine if carcass deposition causes mortality in these two taxa of benthic invertebrates. The probability of mortality for caddisflies was 3.15 times higher in carcass treatments as compared to controls, while amphipod mortality did not change in response to carcass treatment. Amphipods, which contribute most significantly to fish diets, are unlikely to be reduced in response to carcass deposition, which is confined to a small fraction of the lake where lake trout spawn, limiting the possibility for lake-wide effects. We conclude that carcass deposition is unlikely to alter the availability of invertebrates as a food source for fish in Yellowstone Lake.

Wyoming↗

USGS2014

Spatial variability in survival of adult brook trout within two intensively surveyed headwater stream networks

Headwater stream networks are considered heterogeneous riverscapes, but it is challenging to characterize spatial variability in demographic rates. We estimated site-scale (50 m) survival of adult (>age 1+) brook trout (Salvelinus fontinalis) within two intensively surveyed headwater stream networks by applying an open-population N-mixture approach to count data collected over two consecutive summers. The estimated annual apparent survival rate was 0.37 (95% CI: 0.28–0.46) in one network and 0.31 (95% CI: 0.15–0.45) in the other network. In both networks, trout survival was higher in stream sites characterized by more abundant pool habitats. Trout survival was negatively associated with mean depth in one network and positively associated with stream gradient in the other. Stream temperature was not related to trout survival in either network, possibly because the majority of sites were thermally suitable. A similar analytical approach can be useful for inferring survival rates when count data are available over space and time but individual tagging is not feasible.

Connecticut↗

USGS2015

The role of the geophysical template and environmental regimes in controlling stream-living trout populations

The importance of multiple processes and instream factors to aquatic biota has been explored extensively, but questions remain about how local spatiotemporal variability of aquatic biota is tied to environmental regimes and the geophysical template of streams. We used an individual-based trout model to explore the relative role of the geophysical template versus environmental regimes on biomass of trout ( Oncorhynchus clarkii clarkii ). We parameterized the model with observed data from each of the four headwater streams (their local geophysical template and environmental regime) and then ran 12 simulations where we replaced environmental regimes (stream temperature, flow, turbidity) of a given stream with values from each neighboring stream while keeping the geophysical template fixed. We also performed single-parameter sensitivity analyses on the model results from each of the four streams. Although our modeled findings show that trout biomass is most responsive to changes in the geophysical template of streams, they also reveal that biomass is restricted by available habitat during seasonal low flow, which is a product of both the stream’s geophysical template and flow regime. Our modeled results suggest that differences in the geophysical template among streams render trout more or less sensitive to environmental change, emphasizing the importance of local fish–habitat relationships in streams.

Canadian Journal of Fisheries and Aquatic Sciences↗

USGS2018

Evidence of sound production by spawning lake trout (Salvelinus namaycush) in lakes Huron and Champlain

Two sounds associated with spawning lake trout ( Salvelinus namaycush ) in lakes Huron and Champlain were characterized by comparing sound recordings to behavioral data collected using acoustic telemetry and video. These sounds were named growls and snaps, and were heard on lake trout spawning reefs, but not on a non-spawning reef, and were more common at night than during the day. Growls also occurred more often during the spawning period than the pre-spawning period, while the trend for snaps was reversed. In a laboratory flume, sounds occurred when male lake trout were displaying spawning behaviors; growls when males were quivering and parallel swimming, and snaps when males moved their jaw. Combining our results with the observation of possible sound production by spawning splake ( Salvelinus fontinalis × Salvelinus namaycush hybrid), provides rare evidence for spawning-related sound production by a salmonid, or any other fish in the superorder Protacanthopterygii. Further characterization of these sounds could be useful for lake trout assessment, restoration, and control.

Michigan↗

USGS2021

As the prey thickens: Rainbow trout select prey based upon width not length

Drift-feeding fish are typically considered size-selective predators. Yet, few studies have explicitly tested which aspect of prey “size” best explains size selection by drift-foraging fish. Here, we develop a Bayesian discrete choice model to evaluate how attributes of both prey and predator simultaneously influence size-selective foraging. We apply the model to a large dataset of paired invertebrate drift ( n = 784) and rainbow trout ( Oncorhynchus mykiss ) diets ( n = 1028). We characterized prey “size” using six metrics (length, width, area, hemispherical area, volume, mass) and used pseudo- R 2 to determine which metric best explained observed prey selection across seven taxa. We found that rainbow trout are positively size-selective, they are selecting prey based upon differences in prey width, and size-selectivity increases with fish length. Rainbow trout demonstrated strong selection for the adult and pupae stages of aquatic insects relative to their larval stages. Our study provides strong empirical evidence for size-selective foraging in rainbow trout and demonstrates prey selection is based primarily upon width, not length or area as has been widely reported.

Arizona↗

USGS1971

The stress of Formalin treatments in rainbow trout (Salmo gairdneri) and coho salmon (Oncorhynchus kisutch)

Changes in gill function, acid–base balance and pituitary activation occurring during standard 200&ensp;ppm formalin treatments of juvenile rainbow trout ( Salmo gairdneri ) and coho salmon ( Oncorhynchus kisutch ) were compared. Plasma Cl − , Ca ++ , total CO 2 , and interrenal vitamin C in the trout declined continuously and in proportion to the exposure time, but the salmon were able to maintain these metabolic parameters at approximately initial levels. Blood p H and alkaline reserve regulation of the salmon was also less affected by formalin treatments, especially during prolonged exposures. The oxygen consumption of both species was depressed, but substantially more so in the trout than could be accounted for by decreased ventilation rates. Little frank hemolysis occurred in either species, but there was a significant bilirubinemia in the trout.

Journal of the Fisheries Research Board of Canada↗

USGS1976

Relative effect of two dietary water-soluble analogues of menaquinone on coagulation and packed cell volume of blood of lake trout (Salvelinus namaycush)

Triplicate lots of fingerling lake trout ( Salvelinus namaycush ) (initial mean weight, 5.3 g) were fed a basal, semipurified diet, or this basal diet supplemented with either 1.0 or 2.0 ppm of either menadione sodium bisulfite (MSB) or menadione dimethylpyrimidinol bisulfite (MPB) for 18 wk at 14 C. Neither form of vitamin K had a significant effect on the growth, food conversion, or body composition of the fish.Fish fed 1 ppm of MSB had a significantly higher mean packed cell volume (PCV) than those fed 2 ppm of either analogue. Trout fed 2 ppm of MPB had an intermediate PCV which was not significantly different from that of trout fed either 1 ppm MPB or 2 ppm MSB. A dietary level of 1 ppm MPB (providing an equivalent menaquinone concentration of about 0.5 mg/kg of diet) is sufficient to insure normal coagulation of lake trout blood and a satisfactory PCV.

Journal of the Fisheries Research Board of Canada↗

USGS1976

Optimum level of dietary biotin for growth, feed utilization, and swimming stamina of fingerling lake trout (Salvelinus namaycush)

Triplicate lots of fingerling lake trout ( Salvelinus namaycush ) held at 9 C for 20 wk were fed a semipurified basal diet supplemented with 1% spray-dried egg white or d-biotin at concentrations of 0.1, 0.5, 1.0, or 5.0 ppm. Trout fed the basal diet, either alone or with egg white, grew more slowly and converted feed less efficiently ( P < 0.05) than those fed supplemental biotin. Neither the growth rate nor feed conversion differed significantly among the four groups fed supplemental biotin. However, when forced to swim to exhaustion against controlled water currents, trout fed either basal diet, with or without egg white, or 0.1 ppm supplemental biotin, swam a shorter distance ( P < 0.05) than those fed more biotin. Fish fed 0.5 ppm biotin swam as far as those fed 1.0 ppm, but not as far as those fed 5.0 ppm. These results indicate that young lake trout probably need no more than 0.1 ppm biotin for optimum growth and feed conversion, but require from 0.5 to 1.0 ppm for optimum swimming stamina.

Journal of the Fisheries Research Board of Canada↗

USGS1980

Lake trout ( Salvelinus namaycush ) and sea lamprey ( Petromyzon marinus ) populations in Lake Michigan, 1971-78

Lake trout ( Salvelinus namaycush ) was exterminated in Lake Michigan by the mid-1950s as a result of the combined effects of an intensive fishery and predation by the sea lamprey ( Petromyzon marinus ). The widespread application of lampricide in tributary streams had greatly reduced the abundance of lampreys by the early 1960s, and a program to restore self-sustaining populations of lake trout through stocking of yearlings and fingerlings was initiated in 1965. Although the hatchery-reared fish spawned widely in Lake Michigan each year after 1970, no progeny were observed except in an isolated area in Grand Traverse Bay. During 1971–78, sea lamprey abundance was generally greater in Wisconsin than in other parts of the lake. However, the rate of occurrence of sea lamprey wounds on lake trout dropped dramatically there in 1978 after the Peshtigo River, a tributary to Green Bay, was treated with lampricide. Application of Lake Michigan wounding rates to a regression model relating mortality to lamprey wounding developed from Lake Superior data, yielded lamprey-induced mortality estimates in 1977 of 5% in Michigan plus Indiana (combined) and 31% in Wisconsin; corresponding estimates for 1978 were 5 and 15%. Key words : lake trout, sea lamprey predation, abundance, Lake Michigan

Canadian Journal of Fisheries and Aquatic Sciences↗

USGS1980

Changes in mortality of lake trout ( Salvelinus namaycush ) in Michigan waters of Lake Superior in relation to sea lamprey ( Petromyzon marinus ) predation, 1968-78

Total mortality rates of lake trout ( Salvelinus namaycush ) of age VII and older from eastern Lake Superior were estimated from catch curves of age distributions each year in 1968–78. The instantaneous rate of total mortality Z varied from 0.62 to 2.31&ensp;in close synchrony with sea lamprey ( Petromyzon marinus ) wounding rates on lake trout. The regression of transformed Z on the index of lamprey wounding, accounted for over 89% of the variation in lake trout mortality ( r 2 &ensp;=&ensp;0.893). An iterative method of estimating rates of exploitation u , instantaneous rates of fishing mortality F , K (a constant relating sample catch per unit effort to population size), instantaneous normal natural mortality rate M , and instantaneous rate of mortality due to sea lamprey predation L from the sample catch per unit effort and total catch by the fishery is presented. A second method using the results of a 1970–71 tagging study to estimate the mean F in 1970–77 yielded closely similar results to the above and is presented as corroboration. The estimates of u , F , and M appear to be reasonable. F ranged from 0.17&ensp;in 1974 to 0.42&ensp;in 1969 and M was estimated at 0.26. L varied from 0.21&ensp;in 1974 to 1.70&ensp;in 1968. Management implications of various policies concerning sea lamprey control, exploitation, and stocking are discussed. Key words : lake trout, sea lamprey, lamprey control, mortality, predation, Lake Superior, fishery, management

Canadian Journal of Fisheries and Aquatic Sciences↗

USGS1995

Brown trout avoidance of metals in water characteristic of the Clark Fork River, Montana

The avoidance response of brown trout ( Salmo trutta ) to mixtures of cadmium, copper, lead, and zinc was determined in water simulating the Clark Fork River, Montana. Effects of acidification on the avoidance response were also evaluated. Tests were conducted in a cylindrical chamber that received reference water at one end and metal-contaminated water at the other; a distinct boundary formed at the center where the chamber drained. A 1 × mixture of the four metals (Cd, 1.1&ensp;μg/L; Cu, 12&ensp;μg/L; Pb, 3.2&ensp;μg/L; and Zn, 55&ensp;μg/L) that was representative of the ambient metals concentrations of the Clark Fork River resulted in avoidance by brown trout. Brown trout also avoided 0.5×, 2×, 4×, and 10× mixtures but not a 0.1 × mixture. A reduction in pH from 8.0 to either 7.0, 6.0, or 5.0 resulted in significant avoidance. Avoidance reactions to metals, similar to those observed in our laboratory experiments, may contribute to the depression of brown trout populations in the Clark Fork River.

Canadian Journal of Fisheries and Aquatic Sciences↗

USGS2019

The glycoprotein, non-virion protein, and polymerase of viral hemorrhagic septicemia virus are not determinants of host-specific virulence in rainbow trout

Viral hemorrhagic septicemia virus (VHSV), a fish rhabdovirus belonging to the Novirhabdovirus genus, causes severe disease and mortality in many marine and freshwater fish species worldwide. VHSV isolates are classified into four genotypes and each group is endemic to specific geographic regions in the north Atlantic and Pacific Oceans. Most viruses in the European VHSV genotype Ia are highly virulent for rainbow trout (Oncorhynchus mykiss), whereas, VHSV genotype IVb viruses from the Great Lakes region in the United States, which caused high mortality in wild freshwater fish species, are avirulent for trout. This study describes molecular characterization and construction of an infectious clone of the virulent VHSV-Ia strain DK-3592B from Denmark, and application of the clone in reverse genetics to investigate the role of selected VHSV protein(s) in host-specific virulence in rainbow trout (referred to as trout-virulence).

Virology Journal↗

USGS2018

Reduced thermal tolerance during salinity acclimation in brook trout (Salvelinus fontinalis) can be rescued by prior treatment with cortisol

The aims of this study were to assess whether thermal tolerance of brook trout ( Salvelinus fontinalis ) is affected during seawater (SW) acclimation and to investigate the role of cortisol in osmoregulation and thermal tolerance during SW acclimation. Freshwater (FW)-acclimated brook trout at 18°C ( T acc ) were exposed to SW for 16 days, whilst maintaining a FW control. Fish were examined for critical thermal maximum (CT max ) 0 (before), 2, 5 and 16 days after SW exposure, and sampled at T acc and CT max for analysis of plasma cortisol, glucose and Cl − , gill Na + /K + -ATPase (NKA) activity and heat shock protein 70 (HSP70) abundance, and white muscle water content. At 2 days in SW, CT max was significantly reduced (from 31 to 26°C), and then recovered by 16 days. This transient decrease in thermal tolerance coincided with a transient increase in plasma Cl − and decrease in muscle moisture content. Salinity itself had no effect on gill HSP70 abundance compared with the large and immediate effects of high temperature exposure during CT max testing. To examine the role of cortisol in osmoregulation, brook trout were administered a cortisol implant (5 and 25 μg g −1 CORT) prior to SW exposure. Both CORT doses significantly increased their capacity to maintain plasma Cl − during SW acclimation. Treatment with the 25 μg g −1 CORT dose was shown to significantly improve CT max after 2 days in SW, and CT max was associated with plasma Cl − and muscle moisture content. These findings indicate that brook trout are sensitive to temperature during SW acclimation and that thermal tolerance is associated with ion and water balance during SW acclimation.

Journal of Experimental Biology↗

USGS2025

A partner-driven decision support model to inform the reintroduction of bull trout

Assessments of species reintroductions involve a series of complex decisions that include human perspectives and ecological contexts. Here, we present a reintroduction assessment involving bull trout ( Salvelinus confluentus ) using a structured decision-making process. We approached this assessment by engaging partners representing public utilities, government agencies, and Tribes with shared interests in a potential reintroduction. These individuals identified objectives, decision alternatives, and ecological scenarios that were incorporated into a co-produced simulation-based model of potential reintroduction outcomes. The model included mathematical representations of habitat availability, life history expression, and assumptions regarding constraints on potential bull trout populations. Within each recipient stream, partners chose to explore a wide range of decision alternatives and simulated scenarios affecting reintroduction success. Results suggested that 1) reintroductions using eggs or adults were most optimal, 2) adding more individuals resulted in diminishing returns, 3) access to migratory habitat could improve success, and 4) the diversity of opportunities for life history expression led to improved reintroduction opportunities. In addition, modeled scenarios indicated some recipient streams consistently produced lower abundance of reintroduced bull trout. This work contributes a novel example to a growing portfolio of reintroduction assessments that may inform future conservation for bull trout and many other species facing similar challenges.

Washington↗

USGS1965

Lake trout fin-clipping rates at two national fish hatcheries

The successful stocking of the hatchery-reared lake trout (Salvelinus namaycush) in Lake Superior has imporved the outlook for rehabilitating stocks reduced to an extremely low level by predation from the sea lamprey (Petromyzon marinus). Marking the fish by fin-clipping to determine growth and survival benefits from holding young-of-the-year lake trout in the hatchery overwinter was begun in 1952-53 and continued through 1954-55. Boat and shore--and spring and fall--plants of yearlings were compared in subsequent experiments to reduce costs of planting and improve survival. Hatchery lake trout now are marked primarily to distinguish them from wild fish in assessment of natural reproduction. Year-to-year and local variations of the mark also supply information on individual plants. Recent large increases in numbers of lake trout stocked required development of an efficient, economical system of clipping fins on a mass-production basis. Data on marking rates were collected in 1958-63 at the Bureau of Sport Fisheries and Wildlifes's Pendills Creek and Charlevois National Fish Hatcheries (both in Michigan), where more than 3.5 million fish were fin-clipped.

Progressive Fish-Culturist↗

USGS1950

A contribution to the etiology of ulcer disease of trout

During the fall of 1947 and the late summer of 1948, outbreaks of ulcer disease occurred among brook trout fingerlings at the Leetown station and other hatcheries. From the ulcers, blood, and kidneys of the diseased trout were isolated bacteria which could be successfully cultivated only on media to which blood or fish‐tissue extract had been added. Some characteristics of these bacteria are described. In a series of inoculation experiments, brook, brown, and rainbow trout were infected with pure cultures of the isolated bacteria. When the trout used for these tests were free from a latent infection of B. salmonicida, ulcer disease could be reproduced and the bacteria reisolated in pure culture from the inoculated fish. On the basis of the information on hand, it is believed that the isolated bacteria belong to the genus Hemophilus.

Transactions of the American Fisheries Society↗