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USGS1983

Thymocyte plasma membrane of the rainbow trout, Salmo gairdneri : Associated immunoglobulin and heteroantigens

1. Thymic lymphocytes of the rainbow trout, S. gairdneri were disrupted and a plasma membrane containing fraction isolated by differential and buoyant density centrifugation. 2. Radioiodine introduced into the membrane by the lactoperoxidase catalyzed reaction and immunoglobulin (identified by radioimmunoassay with monoclonal antibody) both copurified in the plasma membrane fraction. 3. Rabbit antibody raised to the plasma membrane fraction showed a strong reaction with trout lymphocytes in immunofluorescence, was mitogenic for trout lymphocytes, and recognized lymphocyte membrane heteroantigens of molecular weight > 70,000 in the thymus and 45,000–95,000 in the head kidney.

Comparative Biochemistry and Physiology, Part B: C↗

USGS1977

Effect on tricaine methanesulfonate (MS-222) on hematocrit values in rainbow trout ( Salmo gairdneri )

1. Anesthesia of rainbow trout ( Salmo gairdneri ) with 70 ppm tricaine methanesulfonate (MS-222) for 3-9 min resulted in a linear increase in hematocrit. 2. Handling of unanesthetized trout caused a higher and more variable hematocrit reading than did exposure to MS-222 for up to 3 min. 3. The range and standard error of hematocrit readings was smallest in trout treated with MS-222 for 1 min.

Comparative Biochemistry and Physiology, Part C: C↗

USGS2012

Identification of the thiamin pyrophosphokinase gene in rainbow trout: Characteristic structure and expression of seven splice variants in tissues and cell lines and during embryo development

Thiamin pyrophosphokinase (TPK) converts thiamin to its active form, thiamin diphosphate. In humans, TPK expression is down-regulated in some thiamin deficiency related syndrome, and enhanced during pregnancy. Rainbow trout are also vulnerable to thiamin deficiency in wild life and are useful models for thiamin metabolism research. We identified the tpk gene transcript including seven splice variants in the rainbow trout. Almost all cell lines and tissues examined showed co-expression of several tpk splice variants including a potentially major one at both mRNA and protein levels. However, relative to other tissues, the longest variant mRNA expression was predominant in the ovary and abundant in embryos. During embryogenesis, total tpk transcripts increased abruptly in early development, and decreased to about half of the peak shortly after hatching. In rainbow trout, the tpk transcript complex is ubiquitously expressed for all tissues and cells examined, and its increase in expression could be important in the early-middle embryonic stages. Moreover, decimated tpk expression in a hepatoma cell line relative to hepatic and gonadal cell lines appears to be consistent with previously reported down-regulation of thiamin metabolism in cancer.

Comparative Biochemistry and Physiology, Part B: B↗

USGS2011

Specificity of DNA vaccines against the U and M genogroups of infectious hematopoietic necrosis virus (IHNV) in rainbow trout (Oncorhynchus mykiss)

Infectious hematopoietic necrosis virus (IHNV) is a fish rhabdovirus that causes significant mortality in salmonid species. In North America IHNV has three major genogroups designated U, M, and L. Host-specificity of the M and U genogroups of IHNV has been established both in the field and in experimental challenges, with M isolates being more prevalent and more virulent in rainbow trout (Oncorhynchus mykiss), and U isolates being more prevalent and highly virulent in sockeye salmon (Oncorhynchus nerka). In this study, efficacy of DNA vaccines containing either M (pM) or U (pU) virus glycoprotein genes was investigated during intra- and cross-genogroup challenges in rainbow trout. In virus challenges at 7 days post-vaccination (early antiviral response), both pM and pU were highly protective against either M or U IHNV. In challenges at 28 days post-vaccination (specific antiviral response), both pM and pU were protective against M IHNV but the homologous pM vaccine was significantly more protective than pU in one of two experiments. At this stage both pM and pU induced comparably high protection against U IHNV challenge. Correlates of protection were also investigated by assessing the expression of the interferon-stimulated gene Mx-1 and the production of neutralizing antibodies (NAbs) following pM or pU DNA vaccination. Mx-1 gene expression, measured at 4 and 7 days post-vaccination as an indicator of the host innate immune response, was found to be significantly higher after pM than pU vaccination in some cases. Neutralizing antibody was produced in response to the two vaccines, but antibody titers did not show consistent correlation with protection. The results show that the rainbow trout innate and adaptive immune responses have some ability to distinguish between the U and M genogroup IHNV, but overall the pM and pU vaccines were protective against both homologous and cross-genogroup challenges.

Fish and Shellfish Immunology↗

USGS2016

Life history variation among four lake trout morphs at Isle Royale, Lake Superior

Life history traits were compared among four morphs of lake trout at Isle Royale, Lake Superior. Of 738 lake trout caught at Isle Royale, 701 were assigned to a morph (119 humpers, 160 leans, 85 redfins, and 337 siscowets) using a combination of statistical analysis of head and body shape and visual assignment. On average, redfins were longer (544 mm), heavier (1,481 g), heavier at length (Wr = 94), more buoyant, and older (22 years) than siscowets (519 mm; 1,221 g; 90; 19 years), leans (479 mm; 854 g; 82; 13 years), and humpers (443 mm; 697 g; 87; 17 years). On average, leans grew from a younger age at length = 0 and shorter length at age = 0, at a faster early growth rate to a longer asymptotic length than the other three morphs, while redfins grew at a slower instantaneous rate and humpers grew to a shorter asymptotic length than other morphs. On average, leans were longer (562 mm) and older (15 years) at 50% maturity than redfins (427 mm, 12 years), siscowets (401 mm, 11 years), or humpers (394 mm, 13 years). Life history parameters did not differ between males and females within each morph. We conclude that differences in life history attributes of lean, humper, redfin, and siscowet morphs of lake trout are consistent with differential habitat use in waters around Isle Royale, Lake Superior.

Michigan↗

USGS2017

Movement patterns and spatial segregation of two populations of lake trout Salvelinus namaycush in Lake Huron

Movement ecology is an important component of life history and population dynamics, and consequently its understanding can inform successful fishery management decision-making. While lake trout populations in Lake Huron have shown signs of recovery from near extinction in recent years, knowledge of their movement behavior remains incomplete. We used acoustic telemetry to describe and compare movement patterns of two Lake Huron lake trout populations: Drummond Island and Thunder Bay. Both populations showed high spawning site fidelity, with no evidence of co-mingling during non-spawning season. Detections between spawning periods were mainly limited to receivers within 100 km of spawning locations, and suggested that the two populations likely remained segregated throughout the year. Drummond Island fish, which spawn inside the Drummond Island Refuge, primarily dispersed east into Canadian waters of Lake Huron, with 79–92% of fish being detected annually on receivers outside the refuge. In contrast, Thunder Bay fish tended to disperse south towards Saginaw Bay. Large proportions (i.e., > 80%) of both populations were available to fisheries outside the management zone containing their spawning location. Thunder Bay fish moved relatively quickly to overwinter habitat after spawning, and tended to repeat the same post-spawning movement behavior each year. The consistent, predictable movement of both populations across management zones highlights the importance of understanding population dynamics to effective management of Lake Huron lake trout.

Journal of Great Lakes Research↗

USGS2020

Evidence of spawning by lake trout Salvelinus namaycush on substrates at the base of large boulders in northern Lake Huron

Identification of lake trout spawning sites has focused on cobble substrates associated with bathymetric relief (e.g., ‘contour’ or ‘slope’ along reefs), but this ‘model’ may be narrow in scope. Previous telemetry work conducted near Drummond Island, USA, Lake Huron, identified egg presence in substrates at the base of large boulders (>1 m diameter); however, the extent of this phenomenon was unknown. Telemetry data paired with multi-beam bathymetry identified a 0.63 km 2 area used by lake trout characterized by low bathymetric relief and numerous (~269) large boulders (>1 m diameter) with small-diameter substrates at their bases. Diver surveys revealed egg presence at all 40 boulders surveyed, exclusively associated with clean gravel-cobble (0.6–42 cm) substrates in undercut areas beneath overhanging edges of boulders and in narrow spaces between adjacent boulders. Egg presence was not associated with boulder or substrate physical characteristics which highlighted the possible importance of interstitial currents. Successful incubation in these habitats was inferred by capture of free embryos and post-embryos the following spring using traps and an electrofishing ROV although at lower densities than at popular spawning habitats nearby (1–3 km away). Free embryos and post-embryos were also caught where eggs were not observed the previous fall including unexpectedly on top of boulders which suggested that post-hatch stages may move more than previously thought. Extensive use of boulder-associated habitats for spawning, egg incubation, and early growth suggested this undescribed habitat type may provide an unanticipated contribution to total available lake trout spawning habitat and recruitment in the Great Lakes.

Lake Huron↗

USGS2021

The path toward consistent achievement of sea lamprey abundance and lake trout marking targets in Lake Ontario, 2000–2019

Lake Ontario boasts a diverse fish community comprised of native and introduced species that support vibrant recreational, commercial and Indigenous fisheries. The effective delivery of a program to assess and control the sea lamprey ( Petromyzon marinus ) is crucial to achievement of Lake Ontario Fish Community Objectives of rehabilitating native fish stocks while protecting and maintaining the abundance of introduced salmonines. During 2000–2019, the Great Lakes Fishery Commission (GLFC) and its control agents, Fisheries and Oceans Canada (DFO) and the U. S. Fish and Wildlife Service (USFWS), delivered a consistent program of sea lamprey assessment and control. Beginning in 2004, rising sea lamprey abundance and marking rates on lake trout ( Salvelinus namaycush ) in Lake Ontario coincided with a decline of large lake trout in gillnet surveys. Efforts were undertaken to identify and control important sources of juvenile sea lampreys, including larvae that survived treatment, inhabited deepwater areas, or colonised previously uninhabited stream reaches and tributaries. A renewed reliance on proven conventional controls, including lampricide treatments and barriers, has resulted in consistent suppression of sea lamprey abundance and lake trout marking to prescribed targets in Lake Ontario during 2014–2019. This achievement is unprecedented in the 49-year history of Sea Lamprey Control Program delivery in Lake Ontario, and is attributable to the collaborative efforts of the GLFC, the control agents, and federal, provincial, state, and Indigenous partners.

Lake Ontario↗

USGS2023

Habitat selection by lake trout at reefs near Drummond Island, Lake Huron: An evaluation of physical characteristics used for spawning

Continued dependence on stocking of hatchery-reared lake trout, Salvelinus namaycush , in the Laurentian Great Lakes indicates recruitment bottlenecks still exist between spawning and the juvenile life stage (age-1). Possible impediments include poor habitat quality and an inability of hatchery-origin adults to select substrates that support successful incubation. Understanding of characteristics of suitable lake trout spawning habitat is limited but has centered on the cobble-contour framework, which identifies sloped reefs with cobble substrate and deep interstices to entrain eggs as spawning habitat. A novel sampling design based on acoustic-telemetry detections was used to evaluate relative importance of cobble-contour habitat characteristics (substrate size, homogeneity, interstitial depth, and slope) for predicting egg presence on two spawning reefs in northern Lake Huron. Fixed effect logistic regression models were used to relate egg presence to all possible combinations of measured physical characteristics. Physical characteristics of sites with naturally spawned eggs present varied, and no single best model predicted egg presence. Model selection and multi-model inference revealed slope to be the only informative predictor. Substrate size, homogeneity, and interstitial depth were not important. Embryo survival-to-hatch was also compared among sampling sites using in situ habitat bioassays seeded with hatchery fertilized embryos. No difference in embryo survival was observed between sites where naturally spawned eggs were present vs. absent. Over half of sites evaluated exceeded 75% survival. Naturally spawned eggs were observed at 25 of 57 sites. We suspect other characteristics such as interstitial flow could be helpful for predicting selection of lake trout spawning habitats.

Michigan↗

USGS2025

How quickly do brook trout lose long-term thermal acclimation?

Abundances of coldwater adapted stream fish populations are declining largely due to anthropogenic influences, including increased temperature. To persist in streams with unsuitable thermal habitat, fish must move to coldwater patches, acclimate, or adapt to water temperatures above thermal optima. Brook trout, a coldwater adapted salmonid, has previously displayed physiological plasticity and the ability for reversible thermal acclimation when reared at higher temperatures. However, because stream temperatures are not static, it is important to explore the rate at which thermal acclimation occurs to evaluate whether prior thermal experience will influence future thermal performance. To determine the temporal scale in loss of thermal acclimation as water temperatures cool, we acclimated brook trout to three thermal regimes: +0 °C (ambient; mimicking the daily average water temperature of a nearby long-term study site), as well as +2 °C and +4 °C above ambient. After 2 years of being reared under those conditions, fish from the warmer treatments were moved to a common, colder temperature (ambient). We then used critical thermal maximum to measure the loss in acclimation response of fish from each treatment over time. We found that regardless of initial acclimation temperature, thermal tolerance of warm acclimated fish decreased rapidly for 1 week, then gradually decreased, and was completely lost within 42 days. This gradual loss of acclimation may be valuable to persistence in warmer streams and will be important to include in models of the impact climate change has on brook trout and other aquatic ectotherms with significant thermal plasticity.

Massachusetts↗

USGS2011

In vivo fitness correlates with host-specific virulence of Infectious hematopoietic necrosis virus (IHNV) in sockeye salmon and rainbow trout

The relationship between virulence and overall within-host fitness of the fish rhabdovirus Infectious hematopoietic necrosis virus (IHNV) was empirically investigated in vivo for two virus isolates belonging to different IHNV genogroups that exhibit opposing host-specific virulence. U group isolates are more virulent in sockeye salmon and M group isolates are more virulent in rainbow trout. In both single and mixed infections in the two fish hosts, the more virulent IHNV type exhibited higher prevalence and higher viral load than the less virulent type. Thus, a positive correlation was observed between higher in vivo fitness and higher host-specific virulence in sockeye salmon and rainbow trout. Comparisons of mean viral loads in single and mixed infections revealed no evidence for limitation due to competition effects between U and M viruses in either rainbow trout or sockeye salmon co-infections.

Virology↗

USGS2021

Effects of long-term cortisol treatment on growth and osmoregulation of Atlantic salmon and brook trout

Cortisol is the final product of the hypothalamic-pituitary-interrenal (HPI) axis and acts as a gluco- and mineralo-corticoid in fish. Long-term elevations of cortisol have been linked to reduced growth in fishes, but the mechanism(s) and relative sensitivities of species are still unclear. We carried out experiments to examine the relative effects of cortisol on growth and gill NKA activity in two salmonids: Atlantic salmon ( Salmo salar ) and brook trout ( Salvelinus fontinalis ). Treatment with intraperitoneal cortisol implants for 30 days resulted in reduced growth in both species, but with greater sensitivity to cortisol in brook trout. Gill NKA activity was strongly upregulated by cortisol in Atlantic salmon, and weakly upregulated in brook trout but with no statistically significant effect. Cortisol treatment resulted in reduced plasma levels of insulin-like growth factor I and increased plasma growth hormone levels in Atlantic salmon. Our results demonstrate that there are species differences in the sensitivity of growth and osmoregulation to cortisol, even among species in the same family (Salmonidae).

General and Comparative Endocrinology↗

USGS2003

Classifying sea lamprey marks on Great Lakes lake trout: observer agreement, evidence on healing times between classes and recommendations for reporting of marking statistics

In 1997 and 1998 two workshops were held to evaluate how consistent observers were at classifying sea lamprey ( Petromyzon marinus ) marks on Great Lakes lake trout ( Salvelinus namaycush ) as described in the King classification system. Two trials were held at each workshop, with group discussion between trials. Variation in counting and classifying marks was considerable, such that reporting rates for A1–A3 marks varied two to three-fold among observers of the same lake trout. Observer variation was greater for classification of healing or healed marks than for fresh marks. The workshops highlighted, as causes for inconsistent mark classification, both departures from the accepted protocol for classifying marks by some agencies, and differences in how sliding and multiple marks were interpreted. Group discussions led to greater agreement in classifying marks. We recommend ways to improve the reliability of marking statistics, including the use of a dichotomous key to classify marks. Laboratory data show that healing times of marks on lake trout were much longer at 4°C and 1°C than at 10°C and varied greatly among individuals. Reported A1–A3 and B1–B3 marks observed in late summer and fall collections likely result from a mixture of attacks by two year classes of sea lamprey. It is likely that a substantial but highly uncertain proportion of attacks that occur in late summer and fall lead to marks that are classified as A1–A3 the next spring. We recommend additional research on mark stage duration.

Journal of Great Lakes Research↗

USGS2005

Embryonic developmental progression in lake trout ( Salvelinus namaycush ) (Walbaum, 1792) and its relation to lake temperature

Developmental progression of lake trout ( Salvelinus namaycush ) embryos was examined with light and scanning electron microscopy. From this examination, key developmental stages were described in detail. The key developmental stages were then applied to individual lake trout egg lots incubated in constant temperatures of 2, 4, 6, 8, and 10°C. We used Belehradek's, Thermodynamic, and Power models, and also developed the Zero model to determine stage specific developmental rates of lake trout eggs for each background temperature. From the models, hatch dates and staging were predicted for temperature regimes from Lake Superior (1990–91) and Lake Huron (1996–97). Based on the existing lake temperature data and the observed spawning dates, the Zero and the Power models predict that post peak spawning may contribute significantly to overall recruitment success for these years.

Journal of Great Lakes Research↗

USGS1990

Recovery of an offshore lake trout ( Salvelinus namaycush ) population in eastern Lake Superior

The lake trout ( Salvelinus namaycush ) population at Stannard Rock, Michigan, an isolated offshore reef in eastern Lake Superior, was monitored each spring from 1959–79 using a permit assessment gill net fishery. This population, like nearly all of those in inshore waters, declined to low levels during the years of intense predation by the sea lamprey ( Petromyzon marinus ) in the late 1950s and early 1960s. After sea lamprey control began in 1961, the abundance of native lake trout at Stannard Rock began to increase slowly in the 1960s and was limited to recruitment into the fishable stock of native fish that were juveniles during the years of high sea lamprey activity. By the early 1970s, lake trout abundance increased sharply and remained at a high level. This rapid recovery resulted from several strong year classes produced by the small spawning aggregations that reached maturity in the 1960s. Reproduction occurred in all years during and after the peak of sea lamprey activity in 1959. The strengths of year classes produced in 1963–1968 were related to the relative abundance of spawners the previous fall.

Journal of Great Lakes Research↗

USGS1995

Density-independent survival of wild lake trout in the Apostle Islands area of Lake Superior

The lake trout ( Salvelinus namaycush ) stock at Gull Island Shoal in western Lake Superior was one of only a few stocks of lean lake trout in the Great Lakes that survived overfishing and predation by the sea lamprey ( Petromyzon marinus ). Since the mid 1960s, the abundance of wild recruits measured at age 0 and the number of age-7 to -11 wild fish recruited to the fishable stock have increased. We used the Varley-Gradwell method to test for density-dependent survival between these life stages. Survival from age-0 to ages 7–11 was not affected by increasing density, which suggests that further increases in recruitment and stock size are still possible. We suggest that testing for the existence of density-dependent survival can be used to indicate when lake trout populations are rehabilitated.

Journal of Great Lakes Research↗

USGS1995

Comparison of lake trout-egg survival at inshore and offshore and shallow-water and deepwater sites in Lake Superior

We incubated lake trout ( Salvelinus namaycush ) eggs over winter at shallow (10 m) and deep locations (20 m) on Gull Island Shoal, Lake Superior; at a shallow-water (10 m) site off the mainland (Bark Point); and in flowing Great Lakes water at two laboratories. Survival to hatch was significantly higher in the laboratories and averaged 80.9%. In Lake Superior, egg survival among incubators at all sites was significantly higher (P < 0.0001) for incubators that remained buried in spawning substrates (15.1–21.0%) than for incubators that were partially or completely exposed to water currents (1.0–12.6%). Egg survival for incubators that remained buried at the shallow-water sites was significantly higher at Bark Point (44.6%) than at Gull Island Shoal (21.0%). Egg survival among incubators that remained buried at the deep (14.4%) and shallow-water sites (21.0%) on Gull Island Shoal was not significantly different. Because incubators that were completely buried or partially exposed only appeared to differ in their degree of exposure, we concluded that survival of eggs in the lake was reduced by mechanical stress associated with water turbulence. Lower egg survival at Gull Island Shoal, a known lake trout-spawning site, was not expected and appeared to have been caused by a strong gale that occurred when these eggs were in late epiboly, a sensitive embryological stage. We present a hypothesis suggesting that lake trout recruitment in the Great Lakes is limited by availability of spawning habitat.

Journal of Great Lakes Research↗

USGS1995

Lake trout restoration in the Great Lakes: stock-size criteria for natural reproduction

We examined the question of whether the lake trout restoration program in the Great Lakes has developed brood stocks of adequate size to sustain natural reproduction. Stock size criteria were developed from areas of the Great Lakes where natural reproduction has been successful (defined as detection of age-1 or older recruits by assessment fishing). We contrasted them with stocks in areas with no natural reproduction. Based on the relative abundance of spawners measured in the fall and the presence or absence of natural reproduction in 24 areas of the Great Lakes, we found three distinct sets of lake trout populations. In seven areas of successful natural reproduction, the catch-per-unit-effort (CPE) of spawners ranged from 17 to 135 fish/305 m of gillnet. Stock sizes in these areas were used as a gauge against which stocks in other areas were contrasted. We conclude that stock densities of 17-135 fish/305 m of gill net are adequate for natural reproduction, provided that all other requirements are met. No natural reproduction has been detected in seven other areas, where CPEs of spawners ranged from only 3 to 5 fish/305 m. We conclude that spawning stocks of only 3-5 fish/305 m of net are inadequate to develop measurable natural reproduction. Natural reproduction has also not been detected in ten areas where CPEs of spawners ranged from 43 to 195 fish/305 m of net. We conclude that spawning stocks in these ten areas were adequate to sustain natural reproduction, but that some factor other than parental stock size prevented recruitment of wild lake trout.

Journal of Great Lakes Research↗