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At least 1,045 records · Page 58Linked to original sources
USGS2011

Age at sexual maturity, sex ratio, fecundity, and longevity of isolated headwater populations of westslope cutthroat trout

We sampled 19 isolated headwater populations of westslope cutthroat trout Oncorhynchus clarki lewisi in Montana to provide estimates of fecundity, longevity, sex ratio, and age at sexual maturity. Fecundity was estimated for 31 fish collected from two streams in the upper Missouri River drainage. Females smaller than 149 mm fork length (FL) were generally immature and their fecundities could not be estimated. Mean fecundities (SD) were 227 eggs (41.1) for 150–174-mm fish, 346 eggs (85.6) for 175–199-mm fish, and 459 eggs (150.8) for 200-mm and larger fish. A linear regression model (two stream samples combined) to predict fecundity ( E ) from fork length was developed ( E = −494.9 + 4.4sFL; r 2 = 0.51, P < 0.001) for westslope cutthroat trout in the upper Missouri River drainage. Regression slopes of fecundity against fish length differed significantly ( P < 0.01) between these and some of the previously studied populations. Steeper slopes were associated with lacustrine-adfluvial populations. The average sex ratio was 1.3 males per female across all sampled streams. Males began to mature sexually at age 2 and all were mature by age 4. Some females (27%) were sexually mature at age 3 and most of them (93%) were mature by age 5. Length was a better predictor of sexual maturity than age. Males matured at 110–160 mm and females at 150–180 mm FL. The maximum estimated age was 8 years based on otoliths from 475 fish collected from our 19 study streams and 14 additional streams.

Montana↗
USGS2000

Effects of a spring flushing flow on the distribution of radio-tagged juvenile rainbow trout in a Wyoming tailwater

The controlled release of dammed water, designed to produce a flushing flow that would remove fine sediments from spawning habitat in a flow-regulated river, did not displace juvenile rainbow trout Oncorhynchus mykiss (20-25 cm total length) downstream. Of eight naturally spawned (wild) and nine hatchery fish that were radio-tagged, only one wild fish and two hatchery fish were found in different locations after an eight-fold increase in flow. These three fish moved upstream and the greatest movement was 96 m. Cobble and boulder substrates in main-channel pools were thought to provide slow-water-velocity refuges during the flushing flow. Our findings and the findings of other researchers suggest that flushing flows can be conducted to enhance spawning habitat for rainbow trout without causing extensive downstream movements or habitat displacement of small fish in regulated rivers.

North American Journal of Fisheries Management↗
USGS2004

Tag Retention and Survivorship of Hatchery Rainbow Trout Marked with Large-Format Visible Implant Alphanumeric Tags

Large-format visible implant alphanumeric (VIalpha) tags were implanted into 15,400 rainbow trout Oncorhynchus mykiss. Tag retention after 25 d was 82.6%, and survivorship was 92.8%. The results of this study compare favorably with those of similar studies on other species and suggest that large-format VIalpha tags are an appropriate choice for studies requiring the individual identification of larger rainbow trout.

North American Journal of Aquaculture↗
USGS2006

Virulence comparisons of infectious hematopoietic necrosis virus U and M genogroups in sockeye salmon and rainbow trout

Infectious hematopoietic necrosis virus (IHNV) is an aquatic rhabdovirus that infects salmonids in the Pacific Northwest of the United States, Europe, and Asia. Isolates of IHNV have been phylogenetically classified into three major viral genogroups, designated U, M, and L. To characterize virulence of IHNV in the context of these three viral genogroups, seven strains of IHNV (three U genogroup strains, three M strains, and one L strain) were compared for their pathogenicity in juvenile sockeye salmon Oncorhynchus nerka, kokanee (lacustrine sockeye salmon), and rainbow trout O. mykiss. Fish were waterborne-exposed to the different viral strains, and virulence was assessed by comparing mortality curves and final cumulative percent mortality (CPM) in both species of fish at 10??C and 15??C. In sockeye salmon and kokanee, the U genogroup virus types were extremely virulent, causing average CPMs of 69-100%, while the M genogroup virus types caused very little or no mortality (CPM = 0-4%). The endangered Redfish Lake sockeye salmon stock exhibited extreme differences in susceptibility to the U and M genogroups. Conversely, in two stocks of rainbow trout, the M genogroup virus types were more virulent, inducing average CPMs of 25-85%, while the U genogroup viruses caused lower mortality (CPM = 5-41%). In both fish species, the single L genogroup strain caused low to intermediate mortality (CPM = 13-53%). Viral glycoprotein sequence comparisons of the seven challenge strains revealed three amino acid sites (247, 256, and 270) that consistently differed between the U and M genogroups, possibly contributing to pathogenicity differences. ?? Copyright by the American Fisheries Society 2006.

Journal of Aquatic Animal Health↗
USGS2007

Genetic diversity of infectious hematopoietic necrosis virus from Feather River and Lake Oroville, California, and virulence of selected isolates for Chinook salmon and rainbow trout

Infectious hematopoietic necrosis virus (IHNV) is a significant pathogen of young salmonid fishes worldwide but particularly within the historical range of the Pacific Northwest and California. In the Sacramento and San Joaquin River drainages of California, IHNV outbreaks in juvenile Chinook salmon Oncorhynchus tshawytscha have been observed regularly at large production hatcheries, including Coleman National Fish Hatchery (established in 1941) and Feather River State Fish Hatchery (FRH; established in 1967), since facility operations began. Recent severe epidemics at the FRH in 1998 and 2000-2002 prompted investigations into the characteristics and potential sources of virus at this facility. Both phylogenetic analyses of a variable portion of the glycoprotein gene and serologic comparisons based on neutralization with three polyclonal rabbit sera were used to characterize 82 IHNV isolates from the Feather River watershed between 1969 and 2004. All isolates examined were in the L genogroup and belonged to one of three serologic groups typical of IHNV from California. The IHNV isolates from the Feather River area demonstrated a maximum nucleotide sequence divergence of 4.0%, and new isolates appeared to emerge from previous isolates rather than by the introduction of more diverse subgroups from exogenous sources. The earliest isolates examined from the watershed formed the subgroup LI, which disappeared coincidently with a temporal shift to new genetic and serologic types of the larger subgroup LII. Experimental challenges demonstrated no significant differences in the virulence for juvenile Chinook salmon and rainbow trout O. mykiss from selected isolates representing the principal types of IHNV found historically and from recent epidemics at FRH. While most isolates were equally virulent for both host species, one isolate was found to be more virulent for Chinook salmon than for rainbow trout. ?? Copyright by the American Fisheries Society 2007.

Journal of Aquatic Animal Health↗
USGS2004

Evaluation of three gears for sampling spawning populations of rainbow trout in a large Alaskan river

Alternatives to electrofishing are needed for sampling sexually mature rainbow trout Oncorhynchus mykiss during the spawning season in large Alaskan rivers. We compared hook and line, beach seining, and actively fished gill nets as sampling tools. Beach seining and active gill netting yielded similar catch rates, length frequencies, and sex ratios of sexually mature fish. Hook-and-line sampling was less effective, with a lower catch rate and selectivity for immature fish and sexually mature females. We conclude that both beach seining and active gill netting can serve as alternatives to electrofishing for sampling sexually mature rainbow trout stocks during the spawning season in large rivers with stable spring flows and spawning areas with few snags.

North American Journal of Fisheries Management↗
USGS2007

Assessment of gaseous CO2 and AQUI-S as anesthetics when surgically implanting radio transmitters into cutthroat trout

Tricaine methanesulfonate (MS-222) and CO2 are anesthetics that can be legally used in fisheries work in the United States, but they are limited in their field applications. A mandatory 21-d withdrawal period is required for fish exposed to MS-222. Carbon dioxide is not approved by the U.S. Food and Drug Administration, but it is a "low regulatory priority drug" that can be used legally for fish anesthesia. However, stressful induction and lengthy recovery times have been associated with CO2. AQUI-S is a clove oil derivative that has the potential to become an approved anesthetic without the limitations of MS-222 or CO2. We compared the efficacy of CO2 with that of AQUI-S when surgically implanting radio transmitters into cutthroat trout Oncorhynchus clarkii. A 20% survival rate was observed when CO2 was used in combination with silk sutures, but a 100% survival rate was observed when CO2 was used in combination with surgical staples to shorten the duration of the surgical procedure. A 100% survival rate was observed when AQUI-S was used in combination with either silk sutures or surgical staples. Carbon dioxide in combination with surgical staples seemed to provide a reasonable option when surgically implanting radio transmitters into cutthroat trout, but AQUI-S may be the preferred anesthesia because high pH and dissolved oxygen levels and low free-CO2 concentrations are maintained during surgical procedures.

North American Journal of Fisheries Management↗
USGS2008

Effect of artificial sunlight on the retention of external calcein marks on lake trout

When choosing a fish marking technique to address fishery related questions, it is important to consider factors that affect mark retention. Calcein, a chemical marking agent, is under investigation for potential use on fish. Two laboratory trials were conducted with calcein-marked lake trout Salvelinus namaycush to determine the effect of artificial sunlight on calcein mark intensity. In trial 1, fish exposed to 18,000 lx for 7 d lost 90% or more of the calcein mark intensity (relative to the colorimetric key, mg/L) on the head, body, ventral region, and pectoral fins relative to mark intensity in fish that were maintained in darkness. In trial 2, light intensity was reduced 2.5-3.0-fold. After 7 d of light exposure, calcein mark intensity on the head was reduced by 40-45% relative to mark intensity in fish that were held in darkness; by day 14, calcein mark intensity on the head was reduced by 55-60% relative to that of dark-treated fish. No further decline was observed in light-exposed fish, and head mark intensity values did not differ among days 14, 21, and 28 for this treatment group. Of the four areas evaluated, the head and pectoral fin were more easily read using a colorimetric key than the lateral or ventral regions of the fish. The concentration of calcein spotted on filter paper to devise the colorimetric key ranged from 1 to 100 mg/L. A difference of approximately 7 mg/L in apparent calcein mark intensity means for the head region could be detected using the colorimetric key. These trials showed that calcein mark intensity on lake trout declined when fish were exposed to artificial sunlight, and the use of a colorimetric key improved the objectivity of calcein mark intensity assessment.

North American Journal of Fisheries Management↗
USGS2008

Length variation in age-0 westslope cutthroat trout at multiple spatial scales

Phenotypic diversity provides ecological and evolutionary functions, stabilizing populations in variable environments. Although benefits of larger body size in juvenile fishes are well documented, size variation may have value as well. We explored the distribution of length and length variation in age-0 westslope cutthroat trout Oncorhynchus clarkii lewisi at three spatial scales: area (102 km2), stream (101 km2), and site (100 km2). In addition, we examined relationships between length variables (mean length and interquartile range of length) and instream (temperature and conductivity) and landscape (aspect, elevation, headwater distance, and valley width) variables that were expected to be associated with fish size. Conductivity was included as a surrogate for productivity. Most variation in mean length and interquartile range of fish length was found among areas (62.2% and 62.6%, respectively). Mean length also varied among streams and sites (21.9% and 15.8%, respectively). Similarly, interquartile range of fish length varied among streams and sites (19.1% and 18.3%, respectively). Both length variables were associated with temperature and elevation. Mean fish length was also associated with conductivity, but the association between interquartile length range and conductivity was weak. We conclude that the conservation of variation in phenotypic attributes, such as length, in westslope cutthroat trout may require conservation of viable populations across broad areas and across environmental gradients that are associated with growth. ?? Copyright by the American Fisheries Society 2008.

North American Journal of Fisheries Management↗
USGS2011

Observer error structure in bull trout redd counts in Montana streams: Implications for inference on true redd numbers

Despite the widespread use of redd counts to monitor trends in salmonid populations, few studies have evaluated the uncertainties in observed counts. We assessed the variability in redd counts for migratory bull trout Salvelinus confluentus among experienced observers in Lion and Goat creeks, which are tributaries to the Swan River, Montana. We documented substantially lower observer variability in bull trout redd counts than did previous studies. Observer counts ranged from 78% to 107% of our best estimates of true redd numbers in Lion Creek and from 90% to 130% of our best estimates in Goat Creek. Observers made both errors of omission and errors of false identification, and we modeled this combination by use of a binomial probability of detection and a Poisson count distribution of false identifications. Redd detection probabilities were high (mean = 83%) and exhibited no significant variation among observers (SD = 8%). We applied this error structure to annual redd counts in the Swan River basin (1982&ndash;2004) to correct for observer error and thus derived more accurate estimates of redd numbers and associated confidence intervals. Our results indicate that bias in redd counts can be reduced if experienced observers are used to conduct annual redd counts. Future studies should assess both sources of observer error to increase the validity of using redd counts for inferring true redd numbers in different basins. This information will help fisheries biologists to more precisely monitor population trends, identify recovery and extinction thresholds for conservation and recovery programs, ascertain and predict how management actions influence distribution and abundance, and examine effects of recovery and restoration activities.

Montana↗
USGS2011

Morphological variation of siscowet lake trout in Lake Superior

Historically, Lake Superior has contained many morphologically distinct forms of the lake trout Salvelinus namaycush that have occupied specific depths and locations and spawned at specific times of the year. Today, as was probably the case historically, the siscowet morphotype is the most abundant. Recent interest in harvesting siscowets to extract oil containing omega-3 fatty acids will require additional knowledge of the biology and stock structure of these lightly exploited populations. The objective of this study was to determine whether shape differences exist among siscowet populations across Lake Superior and whether these shape differences can be used to infer stock structure. Morphometric analysis (truss protocol) was used to differentiate among siscowets sampled from 23 locations in Lake Superior. We analyzed 31 distance measurements among 14 anatomical landmarks taken from digital images of fish recorded in the field. Cluster analysis of size-corrected data separated fish into three geographic groups: The Isle Royale, eastern (Michigan), and western regions (Michigan). Finer scales of stock structure were also suggested. Discriminant function analysis demonstrated that head measurements contributed to most of the observed variation. Cross-validation classification rates indicated that 67&ndash;71% of individual fish were correctly classified to their region of capture. This is the first study to present shape differences associated with location within a lake trout morphotype in Lake Superior.

Transactions of the American Fisheries Society↗
USGS2011

Effects of fish size, habitat, flow, and density on capture probabilities of age-0 rainbow trout estimated from electrofishing at discrete sites in a large river

We estimated size-specific capture probabilities of age-0 rainbow trout Oncorhynchus mykiss in the Lee's Ferry Reach of the Colorado River, Arizona, by backpack and boat electrofishing at discrete shoreline sites using both depletion and mark-recapture experiments. Our objectives were to evaluate the feasibility of estimating capture probability for juvenile fish in larger rivers; to determine how it is influenced by fish size, habitat, flow, density, and recovery period; and to test population closure assumptions. There was no mortality among the 351 rainbow trout that were captured by electrofishing, marked, and held for 24 h. Of a total of 2,966 fish that were marked and released, only 0.61% were captured outside of mark-recapture sites, and total emigration from mark-recapture sites was 2.2-2.6%. These data strongly suggest that populations within discrete sites can be treated as effectively closed for the 24-h period between marking and recapture. Eighty percent of capture probability estimates from 66 depletion experiments and 42 mark-recapture experiments ranged from 0.28 to 0.75 and from 0.17 to 0.45, respectively, and the average coefficient of variation of estimates was 0.26. There was strong support for a fish size-capture probability relationship that accounted for the differences in vulnerability across habitat types. Smaller fish were less vulnerable in high-angle shorelines that were sampled by boat electrofishing. There was little support for capture probability models that accounted for within-day and across-month variation in flow. The effects of fish density on capture probability were challenging to discern, variable among habitat types and estimation methodologies, and confounded with the effect of fish size. As capture probability estimates were generally precise and the closure assumption was met, our results demonstrate that electrofishing-based mark-recapture experiments at discrete sites can be used to estimate the abundance of juvenile fish in large rivers.

Arizona↗
USGS2005

The severity of Whirling disease among wild trout corresponds to the differences in genetic composition of tubifex tubifex populations in Central Colorado

We analyzed the geographic distribution of Tubifex tubifex from various river drainages in central Colorado by genetic screening with specific mitochondrial 16S ribosomal DNA (mt 16S rDNA) markers. Four distinct mt 16S rDNA lineages are evident. The sites varied with respect to land- and water-use practices. All sites represented habitats presumed capable of supporting oligochaetes. At the locations where whirling disease has had the greatest impact on resident rainbow trout, T. tubifex, representing lineages I and III (genotypes known to be susceptible to Mxyobolus cerebralis), were most commonly found. In contrast, at sites less affected by whirling disease, T. tubifex of lineages V and VI that are more resistant to M. cerebralis infections were more abundant. The predominance of resistant T. tubifex worms (lineages V and VI) at low-impact sites supports the conclusion that when these genotypes are in greater abundance, the potential for more severe effects of whirling disease on wild rainbow trout populations may be diminished. ?? American Society of Parasitologists 2005.

Journal of Parasitology↗
USGS2012

Low-level copper exposures increase visibility and vulnerability of juvenile coho salmon to cutthroat trout predators

Copper contamination in surface waters is common in watersheds with mining activities or agricultural, industrial, commercial, and residential human land uses. This widespread pollutant is neurotoxic to the chemosensory systems of fish and other aquatic species. Among Pacific salmonids (Oncorhynchus spp.), copper-induced olfactory impairment has previously been shown to disrupt behaviors reliant on a functioning sense of smell. For juvenile coho salmon (O. kisutch), this includes predator avoidance behaviors triggered by a chemical alarm cue (conspecific skin extract). However, the survival consequences of this sublethal neurobehavioral toxicity have not been explored. In the present study juvenile coho were exposed to low levels of dissolved copper (5-20 microg/L for 3 h) and then presented with cues signaling the proximity of a predator. Unexposed coho showed a sharp reduction in swimming activity in response to both conspecific skin extract and the upstream presence of a cutthroat trout predator (O. clarki clarki) previously fed juvenile coho. This alarm response was absent in prey fish that were exposed to copper. Moreover, cutthroat trout were more effective predators on copper-exposed coho during predation trials, as measured by attack latency, survival time, and capture success rate. The shift in predator-prey dynamics was similar when predators and prey were co-exposed to copper. Overall, we show that copper-exposed coho are unresponsive to their chemosensory environment, unprepared to evade nearby predators, and significantly less likely to survive an attack sequence. Our findings contribute to a growing understanding of how common environmental contaminants alter the chemical ecology of aquatic communities.

Ecological Applications↗
USGS2007

Comparative growth and consumption potential of rainbow trout and humpback chub in the Colorado River, Grand Canyon, Arizona, under different temperature scenarios

We used bioenergetics models for humpback chub, Gila cypha, and rainbow trout, Oncorhynchus mykiss, to examine how warmer water temperatures in the Colorado River, Grand Canyon, Arizona, through a proposed selective withdrawal system (SWS) at Glen Canyon Dam, would affect growth, consumption, and predation rates. Consumption by the rainbow trout population was at least 10 times higher than by the smaller humpback chub population. Water temperature increases of 6??C during autumn increased growth of humpback chub and likely increased their survival by reducing the time vulnerable to predation. Water temperature increases caused by drought in 2005 did not alter humpback chub growth as much as the SWS. Increased temperatures might cause changes to the invertebrate community and the distribution and abundance of other warmwater nonnative fishes. The implications on the entire aquatic community need to be considered before any management action that includes increasing water temperatures is implemented.

Southwestern Naturalist↗
USGS2004

Behavioral response of young rainbow trout ( Oncorhynchus mykiss ) to forest fire-retardant chemicals in the laboratory

Fire-retardant chemicals often are applied in relatively pristine and environmentally sensitive areas that are potentially inhabited by endangered or threatened aquatic species. Avoidance of contaminants is an adaptive behavior that may reduce exposure to harmful conditions. We evaluated the avoidance responses of rainbow trout ( Oncorhynchus mykiss ) to concentrations of fire-retardant chemicals and alternate constituent formulations ranging from 0.65 to 26 mg/L. Countercurrent avoidance chambers were used in a flow-through design with receiving water at each end and a drain at the center to create a distinct boundary between treatment water and reference water. Rainbow trout consistently avoided water treated with retardants at all concentrations tested. The magnitude of the avoidance response did not appear to follow a concentration-response relationship, but rather was an all-or-none response.

Environmental Toxicology and Chemistry↗
USGS1963

Some phases of the life history of the trout-perch

The trout-perch, Percopsis omiscomaycus (Walbaum), is one of the more abundant forage fishes in the larger lakes of midwestern United States and central Canada where walleye, Stizostedion v. vitreum (Mitchill), yellow perch, Perca flavescens (Mitchill), and coregonids predominate. It has been suggested that it may have considerable effect on perch and walleye populations of these lakes. The present study describes growth, food habits, population structure, year-class strengths, and reproductive capacity of the trout-perch in relation to its population dynamics in lower Red Lake, Minnesota.

Ecology↗
USGS1995

Dose-response effects of recombinant bovine somatotrop (Posilac) on growth performance and body composition of two-year-old rainbow trout (Oncorhynchus mykiss)

Two hundred rainbow trout ( Oncorhynchus mykiss , mean weight 301.5 g) were allotted to four treatments with five replicates in a randomized block design to determine the dose-response effects of recombinant bovine somatotropin (rbST; Posilac TM ) on growth performance and carcass composition. Treatments were sham-injected controls (S), 10 µ g/g BW of rbST (L), 20 µ g/g BW of rbST (M), and 30 µ g/g BW of rbST (H). The tanks held 135 L; water flow = 15.1 L/min; temperature = 15°C. The fish were maintained in a 12-h light:dark cycle and hand-fed twice daily. The fish received a single intraperitoneal (i.p.) injection on d 0 and were weighed on d 0, 14, 28, and 56. On d 56 the fish were killed. The whole body (WBW), eviscerated carcass (EC), viscera (VIS), and reproductive organ weights and the increase in average daily body length (ADL) were determined. Recombinant bST reduced (linear, P < .004) feed intake 17.6% from d 0 to 14 and improved ADG 44.8% from d 0 to 14 (linear, P < .001) and 8.1% from d 0 to 56 (linear, P < .022). Treated groups had improved (linear, P < .001) feed efficiencies for d 0 to 28. Treatment with rbST increased final weight (linear, P < .018) and length (linear, P < .001), decreased carcass dry matter (linear, P < .001) and fat (linear, P < .001), content, increased carcass ash (linear, P < .001) and tended to increase carcass protein (linear, P < .054) content. Recombinant bST increased WBW (linear, P < .018) and EC (linear, P < .003) but decreased (linear, P < .015) testes weight. Ovary weights, VIS and overall gonadosomatic index were unaffected ( P > .05) by rbST. Recombinant bST was undetectable in serum samples taken on d 56 as determined by radioimmunoassay. Overall, the improved ADG, feed efficiency, body mass, and composition indicate that administration of rbST to rainbow trout may be an efficacious method of modulating growth in fish.

Journal of Animal Science↗