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At least 577 records · Page 32Linked to original sources
USGS2024

Declines in brook trout abundance linked to atmospheric warming in Maryland, USA

Salmonid fishes provide an important indicator of climate change given their reliance on cold water. We evaluated temporal changes in the density of stream-dwelling brook trout ( Salvelinus fontinalis ) from surveys conducted over a 36-year period (1988–2023) by the Maryland Department of Natural Resources in Eastern North America. Nonparametric trend analyses revealed decreasing densities of adult fish (age 1+) in 19 sites (27%) and increases in 5 sites (7%). In contrast, juvenile fish (age 0) densities decreased in 4 sites (6%) and increased in 10 sites (14%). Declining adult brook trout trends were related to atmospheric warming rates during the study period, and this relationship was stronger than the effects of land use change or non-native brown trout. In contrast, juvenile fish trends generally increased with elevation but were not related to air temperature trends or land use change. Our analysis reveals significant changes in several brook trout populations over recent decades and implicates warming atmospheric conditions in population declines. Our findings also suggest the importance of temperature for adult survival rather than recruitment limitation in brook trout population dynamics.

Maryland↗
USGS2018

Exposure-related effects of Zequanox on juvenile lake sturgeon (Acipenser fulvescens) and lake trout (Salvelinus namaycush)

The environmental fate, persistence, and non-target animal impacts of traditional molluscicides for zebra, Dreissena polymorpha , and quagga, D. bugensis , mussel control led to the development of the biomolluscicide Zequanox. Although previous research has demonstrated the specificity of Zequanox, one study indicated sensitivity of salmonids and lake sturgeon, Acipenser fulvescens , following non-label compliant exposures to Zequanox. This study was conducted to evaluate sublethal and lethal impacts of Zequanox exposure on juvenile lake sturgeon and lake trout, Salvelinus namaycush , following applications that were conducted in a manner consistent with the Zequanox product label. Fish were exposed to 50 or 100 mg/L of Zequanox as active ingredient for 8 h and then held for 33 d to evaluate latent impacts. No acute mortality was observed in either species; however, significant latent mortality (P < 0.01, df = 9; 46.2%) was observed in lake trout that were exposed to the highest dose of Zequanox. Statistically significant (P < 0.03, df = 9), but biologically minimal differences were observed in the weight (range 20.17 to 21.49 g) of surviving lake sturgeon at the termination of the 33 d post-exposure observation period. Statistically significant (P < 0.05, df = 9) and biologically considerable differences were observed in the weight (range 6.19 to 9.55 g) of surviving lake trout at the termination of the 33 d post-exposure observation period. Histologic evaluation of lake trout gastrointestinal tracts suggests that the mode of action in lake trout is different from the mode of action that induces zebra and quagga mussel mortality. Further research could determine the sensitivity of other salmonid species to Zequanox and determine if native fish will avoid Zequanox treated water.

Management of Biological Invasions↗
USGS2020

Anadromous coastal cutthroat trout Oncorhynchus clarkii clarkii as a host for Argulus pugettensis (Crustacea, Branchiura): Parasite prevalence, intensity and distribution

Coastal cutthroat trout [ Oncorhynchus clarkii clarkii (Richardson, 1836)] from the marine waters of Puget Sound, WA, was documented as a new host for the ectoparasite Argulus pugettensis ( Dana, 1852 ). The prevalence of A. pugettensis was 66% (49 of 74) on cutthroat trout and 0% (0 of 55) on coho salmon [ O. kisutch (Walbaum, 1792)] collected during the winter of 2017/2018. Infestations occurred most frequently on the dorsal surface, with intensities ranging from 1 to 26 argulids per fish (mean intensity 3.94 ± 4.93 S.D.). In contrast, the prevalence of the common salmon louse [ Lepeophtheirus salmonis (Krøyer, 1837)] was 72% for cutthroat trout and 31% for coho salmon. Relative to other native salmonids, little is known regarding the status, ecology and threats for coastal cutthroat trout. New information reported here is a first step in understanding the relationship between this wild, native trout and infestations by parasitic sea lice and should be followed by future studies aimed to identify population level consequences.

Northwest Science↗
USGS2018

Hydrogeochemical controls on brook trout spawning habitats in a coastal stream

Brook trout ( Salvelinus fontinalis ) spawn in fall and overwintering egg development can benefit from stable, relatively warm temperatures in groundwater-seepage zones. However, eggs are also sensitive to dissolved oxygen concentration, which may be reduced in discharging groundwater (i.e., seepage). We investigated a 2 km reach of the coastal Quashnet River in Cape Cod, Massachusetts, USA, to relate preferred fish spawning habitats to geology, geomorphology, and discharging groundwater geochemistry. Thermal reconnaissance methods were used to locate zones of rapid groundwater discharge, which were predominantly found along the central channel of a wider stream valley section. Pore-water chemistry and temporal vertical groundwater flux were measured at a subset of these zones during field campaigns over several seasons. Seepage zones in open-valley sub-reaches generally showed suboxic conditions and higher dissolved solutes compared to the underlying glacial outwash aquifer. These discharge zones were cross-referenced with preferred brook trout redds and evaluated during 10 years of observation, all of which were associated with discrete alcove features in steep cutbanks, where stream meander bends intersect the glacial valley walls. Seepage in these repeat spawning zones was generally stronger and more variable than in open-valley sites, with higher dissolved oxygen and reduced solute concentrations. The combined evidence indicates that regional groundwater discharge along the broader valley bottom is predominantly suboxic due to the influence of near-stream organic deposits; trout show no obvious preference for these zones when spawning. However, the meander bends that cut into sandy deposits near the valley walls generate strong oxic seepage zones that are utilized routinely for redd construction and the overwintering of trout eggs. Stable water isotopic data support the conclusion that repeat spawning zones are located directly on preferential discharges of more localized groundwater. In similar coastal systems with extensive valley peat deposits, the specific use of groundwater-discharge points by brook trout may be limited to morphologies such as cutbanks, where groundwater flow paths do not encounter substantial buried organic material and remain oxygen-rich.

Hydrology and Earth System Sciences↗
USGS1961

The trout fishery in Shenandoah National Park

Populations of brook trout in streams of Shenandoah National Park were reduced drastically early in the past decade by a succession of unusually severe droughts and floods. The drying of stream beds, predation, and scouring were principal factors in the loss of fish. The park was closed to fishing in 1954 and 1955 to protect survivors. The small numbers of survivors quickly repopulated the streams after drought conditions abated. The stocking of hatchery-reared fingerling trout in selected waters failed to augment the recovery of populations. Survival and growth of young, wild trout were especially good. Their redistribution through miles of previously dry streams was rapid. The park was opened again to fishing in 1956 under regulations which restrict the take but afford an increase in sporting opportunity. Two streams were placed under fishing-for-fun-only regulations in 1961. The welfare of the trout populations is dependent mostly on the weather cycle . Fish may be abundant in wet years but very scarc e in dry ones. Thus, the stream must be managed a s marginal for trout.

Virginia↗
USGS2004

Critical swimming speeds of wild bull trout

We estimated the critical swimming speeds (Ucrit) of wild bull trout at 6??, 11??, and 15??C in laboratory experiments. At 11??C, 5 fish ranging from 11 to 19 cm in length had a mean Ucrit of 48.24 cm/s or 3.22 body lengths per second (BL/s). Also at 11??C , 6 fish from 32 to 42 cm had a mean Ucrit of 73.99 cm/s or 2.05 BL/s. At 15??C, 5 fish from 14 to 23 cm had a mean Ucrit of 54.66 cm/s or 2.88 BL/s. No fish successfully swam at 6??C. Swim speed was significantly influenced by fish length. Many bull trout performed poorly in our enclosed respirometers: of 71 Ucrit tests we attempted, only the 16 described above were successful. Bull trout that refused to swim held station within tunnels by using their pectoral fins as depressors, or they rested and later became impinged against a downstream screen. Several common techniques did not stimulate consistent swimming activity in these fish. Our estimates of U crit for bull trout provide an understanding of their performance capacity and will be useful in modeling efforts aimed at improving fish passage structures. We recommend that fishway or culvert designers concerned with bull trout passage maintain velocities within their structures at or below our estimates of Ucrit, thus taking a conservative approach to ensuring that these fish can ascend migratory obstacles safely.

Northwest Science↗
USGS2008

Pathogens associated with native and exotic trout populations in Shenandoah National Park and the relationships to fish stocking practices

Restrictive fish stocking policies in National Parks were developed as early as 1936 in order to preserve native fish assemblages and historic genetic diversity. Despite recent efforts to understand the effects of non-native or exotic fish introductions, park managers have limited information regarding the effects of these introductions on native fish communities. Shenandoah National Park was established in 1936 and brook trout (Salvelinus fontinalis) restoration within selected streams in the park began in 1937 in collaboration with the Virginia Department of Game and Inland Fisheries (VDGIF). An analysis of tissue samples from brook, brown (Salmo trutta), and rainbow trout (Oncorhynchus mykiss) from 29 streams within the park from 1998–2002 revealed the presence of Renibacterium salmoninarum, Yersinia ruckeri, and infectious pancreatic necrosis virus (IPNv). In order to investigate the relationships of the occurrence of fish pathogens with stocking histories we classified the streams into three categories: 1) streams with no record of stocking, 2) streams that are known to have been stocked historically, and 3) streams that were historically stocked within the park and continue to be stocked downstream of the park boundary. The occurrences of pathogens were summarized relative to this stocking history. Renibacterium salmoninarum, the causative agent of bacterial kidney disease, was the most prevalent pathogen found, occurring in all three species and stream stocking categories, and appears to be endemic to the park. Two other pathogens, Yersinia ruckeri and infectious pancreatic necrosis virus were also described from brook trout populations within the park. IPNv was only found in brook trout populations in streams with prior stocking histories. Yersinia ruckeri was only found in brook trout in steams that have never been stocked and like R. salmoninarum, is likely endemic.

Virginia↗
USGS1987

Sanctuaries for lake trout in the Great Lakes

Populations of lake trout, severely depleted in Lake Superior and virtually extirpated from the other Great Lakes because of sea lamprey predation and intense fishing, are now maintained by annual plantings of hatchery-reared fish in Lakes Michigan, Huron, and Ontario and parts of Lake Superior. The extensive coastal areas of the Great Lakes and proximity to large populations resulted in fishing pressure on planted lake trout heavy enough to push annual mortality associated with sport and commercial fisheries well above the critical level needed to reestablish self-sustaining stocks. The interagency, international program for rehabilitating lake trout includes controlling sea lamprey abundance, stocking hatchery-reared lake trout, managing the catch, and establishing sanctuaries where harvest is prohibited. Three lake trout sanctuaries have been established in Lake Michigan: the Fox Island Sanctuary of 121, 500 ha, in the Chippewa-Ottawa Treaty fishing zone in the northern region of the lake; the Milwaukee Reef Sanctuary of 160, 000 ha in midlake, in boundary waters of Michigan and Wisconsin; and Julian's Reef Sanctuary of 6, 500 ha, in Illinois waters. In northern Lake Huron, Drummond Island Sanctuary of 55, 000 ha is two thirds in Indian treaty-ceded waters in Michigan and one third in Ontario waters of Canada. A second sanctuary, Six Fathom Bank-Yankee Reef Sanctuary, in central Lake Huron contains 168, 000 ha. Sanctuary status for the Canadian areas remains to be approved by the Provincial government. In Lake Superior, sanctuaries protect the spawning grounds of Gull Island Shoal (70, 000 ha) and Devils Island Shoal (44, 000 ha) in Wisconsin's Apostle Island area. These seven sanctuaries, established by the several States and agreed upon by the States, Indian tribes, the U.S. Department of the Interior, and the Province of Ontario, contribute toward solving an interjurisdictional fishery problem.

Conference Paper↗
USGS1994

Ultraviolet-B radiation and the immune response of rainbow trout: Chapter 18

As part of a larger study on global climate change and ozone depletion we are investigating the effects of ultraviolet-B (UVB) radiation on fishes. We conducted a number of experiments to explore the possible effects of UVB radiation on the immune response of juvenile rainbow trout Oncorhynchus mykiss . In one study, the fish developed sunburn and fungal infection on the dorsal skin after exposure to levels of UVB that simulated ambient solar UVB levels observed at mid-latitudes. In a separate study, UVB-exposed rainbow trout with surgically administered dorsal lesions developed fungal infection on the lesions and surrounding skin. Many of these fish subsequently died within a 9 day exposure period. Fish with surgical lesions, but not exposed to UVB radiation, did not develop fungal infection and did not die. In mammals, UVB-induced immunosuppression is thought to occur through the isomerization of urocanic acid or the formation of DNA pyrimidine dimers, or through some interaction between the two. We found a substance that appeared, upon HPLC detection, to be trans-urocanic acid in the skin of UVB-exposed and unexposed rainbow trout. Neurotransmitter stimulation of adrenoceptors may be involved in changes in pigmentation observed in UVB-exposed fishes. We measured adrenoceptors in skin membranes from rainbow trout exposed to UVB and found a decrease in cz2-adrenoceptors compared with fish not exposed to UVB. Results of our study indicate that prolonged exposure of juvenile rainbow trout to mid-latitude levels of solar UVB may play an important role in the initiation of certain disease outbreaks and may decrease survival of fish that have lesions on the dorsal skin.

Conference Paper↗
USGS2014

Restoration of Rio Grande cutthroat trout Oncorhynchus clarkii virginalis to the Mescalero Apache Reservation

Rio Grande Cutthroat trout Oncorhynchus clarkii virginalis (RGCT) represents the most southern subspecies of cutthroat trout, endemic to Rio Grande, Canadian, and Pecos basins of New Mexico and southern Colorado. The subspecies currently occupies less than 12% of its historic range. The Mescalero Apache Tribe has partnered with U.S. Geological Survey-New Mexico Cooperative Fish and Wildlife Research Unit, New Mexico State University, U.S. Fish and Wildlife Service, and New Mexico Department of Game and Fish to meet mutually shared goals of restoring and maintaining a Pecos strain of RGCT to Tribal lands. The goal of this project was to assess the suitability of the Rio Ruidoso within the Mescalero Apache Reservation to support a self-sustaining RGCT population by conducting a systematic and comprehensive survey. We conducted three surveys (fall 2010, spring 2011 and 2012) to characterize water quality, macroinvertebrate assemblages, fish communities, and physical habitat (stream size, channel gradient, channel substrate, habitat complexity, riparian vegetation cover and structure, migration barriers to movement). Seven-100 m reaches throughout three major tributaries of the Rio Ruidoso within the Tribal lands were sampled during baseflow conditions October 2010, May 2011, and June 2012. Despite the onset of severe drought in 2011, water quality, physical habitat, and fish populations revealed that the Rio Ruidoso and its three tributaries would most likely support a self-sustaining RGCT population. Pools were abundant (mean, 8.9 pools/100 m), instream woody debris was present (range, 3.8-45.6 pieces/100 m), and instream dataloggers revealed daily maximum stream temperatures rarely exceeded criteria established in New Mexico for coldwater fishes, however, presence of frazil and anchor ice may limit fish distribution in the winter. Aquatic macroinvertebrate samples revealed a community of benthic invertebrates reflective of high quality cool to cold water. Overall densities of brown trout, rainbow trout and brook trout were high (overall mean, 0.23 fish/m2) and in relatively good condition (range of mean relative weight, 84-117). Should the Mescalero Apache Tribe decide to introduce RGCT, prior to chemical treatment, a barrier placed below the confluence of Middle and South forks of the Rio Ruidoso would create approximately 12 km of perennial flow and help protect against invasion of non-native fishes. The North Fork of the Rio Ruidoso is not a good candidate for reintroduction because of easy access by the public to reintroduce non-native fishes into the watershed. Lastly, an annual, long-term monitoring program of RGCT would help document that there was no subsequent incursion of non-native fishes.

Cooperator Science Series↗
USGS2020

Decreases in aluminum toxicity and mortality of caged brook trout in Adirondack Mountain Streams

Mortality of juvenile brook trout and water chemistry were characterized in six western Adirondack streams in northern New York State during spring 2015, 2016, and 2017 and compared with results from comparable tests done between 1980 and 2003 in many of the same streams to assess temporal changes in inorganic monomeric aluminum (Ali) concentrations, Ali-toxicity, and the role of Ali-exposure duration on mortality. Ali concentrations of 2 and 4 micromoles per liter (µmol L-1) corresponded to chronic- and acute-mortality thresholds for brook trout, but prolonged exposure to ≥ 1 µmol Ali L-1 also produced low-to-moderate mortality levels. The variability, mean, and highest Ali concentrations in Buck Creek (BUC) year-round, and in several other streams during spring, decreased significantly over the past 30 years. Predictive models indicate that Ali surpassed highly toxic concentrations at BUC for three to four months annually during 2001–2003 but for only two to three weeks annually during 2015–2017. The current lack of extremely high Ali concentrations indicate toxicity has declined markedly between the 1989–1990, 2001–2003, and 2015–2017 test periods, yet acid- Ali episodes can still cause moderate-to-high levels of brook trout mortality during high springtime flows. Assembled models show how mortality of brook trout in several Adirondack streams likely declined in response to the 1990 Clean Air Act Amendments and offer a means to predict how changes in United States regulations that limit the atmospheric emissions of nitrogen (N) and sulfur (S) oxides, and the deposition of N and S, could affect brook trout survival and impaired stream ecosystems in the western Adirondack region.

New York↗
USGS2023

Evaluating brook trout egg and alevin survival at different temperatures in simulated karst environments with marl sedimentation

Brook trout ( Salvelinus fontinalis ) have been extirpated from many karst-geology streams in West Virginia; however, the causes are not fully understood. Specifically, the impact of calcareous precipitate (marl), which is common in hard-water environments, has not been evaluated as an im- pediment to juvenile survival. Accordingly, two lab-based studies were conducted to determine if brook trout egg and alevin survival is inhibited by marl. In the first study, three aeration treatments were applied to water from a limestone spring source (13–14 C; ~300 mg L–1 hardness), resulting in different pH levels and an increasing degree of marl precipitate. Treatments included raw/untreated (RU; no marl), once-aerated (OA; limited marl), and continuously aerated (CA; significant marl) water. Brook trout eggs obtained from a local hatchery were fertilized and stocked among gravel-filled trays receiving each water type. Mortality occurred faster in CA water where marl coated egg surfaces, but cumulative survival was negligible for all water types. After 53 days, no surviving alevins remained in RU or CA, and 1% survival was observed in OA water. However, extra eggs maintained in a marl-producing system at 8 C without gravel demonstrated >50% survival. A second study was carried out to investigate this discrepancy. Survival was evaluated at three temperatures with and without gravel while producing a thin coating of marl. Increased prevalence of alevin deformities and significantly lower survival were observed at 13.7 C versus 8.1 and 11.2 C, but gravel inclusion did not affect these variables. Potentially harmful effects of marl were observed; however, juvenile brook trout survival was higher during Study 2. This research suggests that brook trout reintroduction efforts in karst-geology streams should be focused on microhabitats with limited marl production and adequate water temperatures for juvenile survival.

Journal of the Southeastern Association of Fish an↗
USGS2023

Effects of hard water precipitates on early life stage brook trout

Brook trout (Salvelinus fontinalis) have been extirpated from many karst-geology streams in West Virginia; however, the causes are not fully understood. Specifically, the impact of calcareous precipitate (marl), which is common in hard-water environments, has not been evaluated as an impediment to juvenile survival. Accordingly, two lab-based studies were conducted to determine if brook trout egg and alevin survival is inhibited by marl. In the first study, three aeration treatments were applied to a limestone spring source (13–14 C; ~300 mg L-1 hardness), resulting in different pH levels and an increasing degree of marl precipitate. Treatments included: raw/untreated (RU; no marl), once-aerated (OA; limited marl), and continuously aerated (CA; significant marl) water. Brook trout eggs obtained from a local hatchery were fertilized and stocked among gravel-filled trays receiving each water type. Mortality occurred faster in CA water where marl coated egg surfaces; however, cumulative survival was negligible for all water types. After 53 days, no surviving alevins remained in RU or CA, and 1% survival was observed in OA water; however, extra eggs maintained in a marl-producing system at 8 C without gravel demonstrated > 50% survival. A second study was carried out to investigate this discrepancy. Survival was evaluated at three temperatures with and without gravel while producing a thin coating of marl. Increased prevalence of alevin deformities and significantly lower survival were observed at 13.7 C versus 8.1 and 11.2 C, but gravel inclusion did not affect these variables. Potentially harmful effects of marl were observed; however, juvenile brook trout survival was higher during Study 2. This research suggests that brook trout reintroduction efforts in karst-geology streams should be focused on microhabitats with limited marl production and adequate water temperatures for juvenile survival.

Hatchery International↗
USGS2025

Great Lakes lake trout (Salvelinus namaycush) thiamine monitoring program annual report

Thiamine deficiency in lake trout ( Salvelinus namaycush ) eggs has been linked to early life-stage mortality in the Great Lakes from the 1960s through the 1990s, potentially affecting lake trout recruitment. In response, the U.S. Geological Survey’s Great Lakes Science Center (GLSC), Eastern Ecological Science Center (EESC), and Columbia Environmental Research Center (CERC), and the State University of New York (SUNY) Brockport, in collaboration with partner agencies, initiated a cooperative monitoring program in the late 1990s to assess thiamine concentrations in lake trout eggs. In 2024, egg thiamine concentrations continued to show high variability across sampling sites. No samples with thiamine concentrations below the 4 nmol/g threshold recommended for successful reproduction were observed in Lakes Superior or Huron. In contrast, between 11% and 88% of lake trout sampled from sites in Lakes Michigan, Ontario, Champlain, and the Finger Lakes had egg thiamine concentrations below this critical threshold. Time series data revealed substantial temporal and spatial variation in mean lake trout egg thiamine concentrations across the Great Lakes region.

Finger Lakes, Great Lakes, Lake Champlain↗
USGS2025

Great Lakes lake trout (Salvelinus namaycush) thiamine monitoring program annual report

Thiamine deficiency in lake trout (Salvelinus namaycush) eggs has been linked to early life-stage mortality in the Great Lakes from the 1960s through the 1990s, potentially affecting lake trout recruitment. In response, the U.S. Geological Survey’s Great Lakes Science Center (GLSC), Eastern Ecological Science Center (EESC), and Columbia Environmental Research Center (CERC), and the State University of New York (SUNY) Brockport, in collaboration with partner agencies, initiated a cooperative monitoring program in the late 1990s to assess thiamine concentrations in lake trout eggs. In 2024, egg thiamine concentrations continued to show high variability across sampling sites. No samples with thiamine concentrations below the 4 nmol/g threshold recommended for successful reproduction were observed in Lakes Superior or Huron. In contrast, between 11% and 88% of lake trout sampled from sites in Lakes Michigan, Ontario, Champlain, and the Finger Lakes had egg thiamine concentrations below this critical threshold. Time series data revealed substantial temporal and spatial variation in mean lake trout egg thiamine concentrations across the Great Lakes region.

Lakes Superior, Michigan, Huron, Erie, Ontario, Ch↗
USGS2023

Is now the time? Review of genetic rescue as a conservation tool for brook trout

Brook trout populations have been declining throughout their native range in the east coast of the United States. Many populations are now distributed in small, isolated habitat patches where low genetic diversity and high rates of inbreeding reduce contemporary viability and long-term adaptive potential. Although human-assisted gene flow could theoretically improve conservation outcomes through genetic rescue, there is widespread hesitancy to use this tool to support brook trout conservation. Here, we review the major uncertainties that have limited genetic rescue from being considered as a viable conservation tool for isolated brook trout populations and compare the risks of genetic rescue with other management alternatives. Drawing on theoretical and empirical studies, we discuss methods for implementing genetic rescue in brook trout that could yield long-term evolutionary benefits while avoiding negative fitness effects associated with outbreeding depression and the spread of maladapted alleles. We also highlight the potential for future collaborative efforts to accelerate our understanding of genetic rescue as a viable tool for conservation. Ultimately, while we acknowledge that genetic rescue is not without risk, we emphasize the merits that this tool offers for protecting and propagating adaptive potential and improving species' resilience to rapid environmental change.

Ecology and Evolution↗
USGS2017

Temporal constraints on the potential role of fry odors as cues of past reproductive success for spawning lake trout

Deciding where to reproduce is a major challenge for most animals. Many select habitats based upon cues of successful reproduction by conspecifics, such as the presence of offspring from past reproductive events. For example, some fishes select spawning habitat following odors released by juveniles whose rearing habitat overlaps with spawning habitat. However, juveniles may emigrate before adults begin to search for spawning habitat; hence, the efficacy of juvenile cues could be constrained by degradation or dissipation rates. In lake trout ( Salvelinus namaycush ), odors deposited by the previous year's offspring have been hypothesized to guide adults to spawning reefs. However, in most extant populations, lake trout fry emigrate from spawning reefs during the spring and adults spawn during the fall. Therefore, we postulated that the role of fry odors in guiding habitat selection might be constrained by the time between fry emigration and adult spawning. Time course chemical, physiological, and behavioral assays indicated that the odors deposited by fry likely degrade or dissipate before adults select spawning habitats. Furthermore, fry feces did not attract wild lake trout to constructed spawning reefs in Lake Huron. Taken together, our results indicate fry odors are unlikely to act as cues for lake trout searching for spawning reefs in populations whose juveniles emigrate before the spawning season, and underscore the importance of environmental constraints on social cues.

Ecology and Evolution↗
USGS2021

Direct and delayed mortality of Ceriodaphnia dubia and rainbow trout following time-varying acute exposures to zinc

The potential for delayed mortality following short-term episodic pollution events was evaluated by exposing cladocerans ( Ceriodaphnia dubia ) and rainbow trout ( Oncorhynchus mykiss ) to zinc (Zn) in various 1- to 48-h and 1- to 96-h exposures, respectively, followed by transferring the exposed organisms to clean water for up to 47 h for C. dubia and up to 95 h for trout for additional observation. For C. dubia , 1-h exposures of up to 3790 µg Zn/L never resulted in mortality during the actual Zn exposures, but by 48 h, a 1-h exposure to 114 µg/L, a concentration similar to the present US national water quality acute criterion for the test water conditions, ultimately killed 70% of C. dubia . With C. dubia , the speed of action of Zn toxicity was faster for intermediate concentrations than for the highest concentrations tested. For rainbow trout, pronounced delayed mortalities by 96 h only occurred following ≥8-h exposures. For both species, ultimate mortalities from Zn exposures ≤8 h mostly presented as delayed mortalities, whereas for exposures ≥24 h, almost all ultimate mortalities presented during the actual exposure periods. With Zn, risks of delayed mortality following exposures to all concentrations tested were much greater for the more sensitive, small-bodied invertebrate ( C. dubia ) than for the less sensitive, larger-bodied fish (rainbow trout). These results, along with previous studies, show that delayed mortality is an important consideration in evaluating risks to aquatic organisms from brief, episodic exposures to some substances. Environ Toxicol Chem 2021;40:2484–2498. © 2021 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC. This article has been contributed to by US Government employees and their work is in the public domain in the USA.

Environmental Toxicology and Chemistry↗