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At least 1,297 records · Page 72Linked to original sources
USGS2014

Atlantic salmon, Salmo salar L. are broadly susceptible to isolates representing the North American genogroups of infectious hematopoietic necrosis virus

Beginning in 1992, three epidemic waves of infectious hematopoietic necrosis, often with high mortality, occurred in farmed Atlantic salmon Salmo salar L. on the west coast of North America. We compared the virulence of eleven strains of infectious hematopoietic necrosis virus (IHNV), representing the U, M and L genogroups, in experimental challenges of juvenile Atlantic salmon in freshwater. All strains caused mortality and there was wide variation within genogroups: cumulative mortality for five U-group strains ranged from 20 to 100%, four M-group strains ranged 30-63% and two L-group strains varied from 41 to 81%. Thus, unlike Pacific salmonids, there was no apparent correlation of virulence in a particular host species with virus genogroup. The mortality patterns indicated two different phenotypes in terms of kinetics of disease progression and final per cent mortality, with nine strains having moderate virulence and two strains (from the U and L genogroups) having high virulence. These phenotypes were investigated by histopathology and immunohistochemistry to describe the variation in the course of IHNV disease in Atlantic salmon. The results from this study demonstrate that IHNV may become a major threat to farmed Atlantic salmon in other regions of the world where the virus has been, or may be, introduced.

Journal of Fish Diseases↗
USGS2014

Wetland management and rice farming strategies to decrease methylmercury bioaccumulation and loads from the Cosumnes River Preserve, California

We evaluated mercury (Hg) concentrations in caged fish (deployed for 30 days) and water from agricultural wetland (rice fields), managed wetland, slough, and river habitats in the Cosumnes River Preserve, California. We also implemented experimental hydrological regimes on managed wetlands and post-harvest rice straw management techniques on rice fields in order to evaluate potential Best Management Practices to decrease methylmercury bioaccumulation within wetlands and loads to the Sacramento-San Joaquin River Delta. Total Hg concentrations in caged fish were twice as high in rice fields as in managed wetland, slough, or riverine habitats, including seasonal managed wetlands subjected to identical hydrological regimes. Caged fish Hg concentrations also differed among managed wetland treatments and post-harvest rice straw treatments. Specifically, Hg concentrations in caged fish decreased from inlets to outlets in seasonal managed wetlands with either a single (fall-only) or dual (fall and spring) drawdown and flood-up events, whereas Hg concentrations increased slightly from inlets to outlets in permanent managed wetlands. In rice fields, experimental post-harvest straw management did not decrease Hg concentrations in caged fish. In fact, in fields in which rice straw was chopped and either disked into the soil or baled and removed from the fields, fish Hg concentrations increased from inlets to outlets and were higher than Hg concentrations in fish from rice fields subjected to the more standard post-harvest practice of simply chopping rice straw prior to fall flood-up. Finally, aqueous methylmercury (MeHg) concentrations and export were highly variable, and seasonal trends in particular were often opposite to those of caged fish. Aqueous MeHg concentrations and loads were substantially higher in winter than in summer, whereas caged fish Hg concentrations were relatively low in winter and substantially higher in summer. Together, our results highlight the importance of habitat, seasonal processes, and wetland management practices on Hg cycling and ecological risk in aquatic ecosystems.

California↗
USGS1980

Crude oil degradation as an explanation of the depth rule

Previous studies of crude oil degradation by water washing and bacterial attack have documented the operation of these processes in many different petroleum basins of the world. Crude oil degradation substantially alters the chemical and physical makeup of a crude oil, changing a light paraffinic low-S "mature" crude to a heavy naphthenic or asphalt base, "immature appearing" high-S crude. Rough calculations carried out in the present study using experimentally determined solubility data of petroleum in water give insight into the possible magnitude of water washing and suggest that the process may be able to remove large amounts of petroleum in small divisions of geologic time. Plots of crude oil gravity vs. depth fail to show the expected correlation of increasing API gravity (decreasing specific gravity) with depth below 2.44 km (8000 ft.). Previous studies which have been carried out to document in-reservoir maturation have used crude oil gravity data shallower than 2.44 km (8000 ft.). The changes in crude oil composition as a function of depth which have been attributed to in-reservoir maturation over these shallower depths, are better explained by crude oil degradation. This study concludes that changes in crude oil composition that result from in-reservoir maturation are not evident from existing crude oil gravity data over the depth and temperature range previously supposed, and that the significant changes in crude oil gravity which are present over the shallow depth range are due to crude oil degradation. Thus the existence of significant quantities of petroleum should not necessarily be ruled out below an arbitrarily determined depth or temperature limit when the primary evidence for this is the change in crude oil gravity at shallow depths. ?? 1980.

Chemical Geology↗
USGS2016

Addressing potential local adaptation in species distribution models: implications for conservation under climate change

Species distribution models (SDMs) have been criticized for involving assumptions that ignore or categorize many ecologically relevant factors such as dispersal ability and biotic interactions. Another potential source of model error is the assumption that species are ecologically uniform in their climatic tolerances across their range. Typically, SDMs to treat a species as a single entity, although populations of many species differ due to local adaptation or other genetic differentiation. Not taking local adaptation into account, may lead to incorrect range prediction and therefore misplaced conservation efforts. A constraint is that we often do not know the degree to which populations are locally adapted, however. Lacking experimental evidence, we still can evaluate niche differentiation within a species' range to promote better conservation decisions. We explore possible conservation implications of making type I or type II errors in this context. For each of two species, we construct three separate MaxEnt models, one considering the species as a single population and two of disjunct populations. PCA analyses and response curves indicate different climate characteristics in the current environments of the populations. Model projections into future climates indicate minimal overlap between areas predicted to be climatically suitable by the whole species versus population-based models. We present a workflow for addressing uncertainty surrounding local adaptation in SDM application and illustrate the value of conducting population-based models to compare with whole-species models. These comparisons might result in more cautious management actions when alternative range outcomes are considered.

Ecological Applications↗
USGS2021

Effects of environmental clutter on synthesized chiropteran echolocation signals in an anechoic chamber

Ultrasonic bat detectors are useful for research and monitoring purposes to assess occupancy and relative activity of bat communities. Environmental “clutter” such as tree boles and foliage can affect the recording quality and identification of bat echolocation calls collected using ultrasonic detectors. It can also affect the transmission of calls and recognition by bats when using acoustic lure devices to attract bats to mist-nets. Bat detectors are often placed in forests, yet automatic identification programs are trained on call libraries using echolocation passes recorded largely from open spaces. Research indicates that using clutter-recorded calls can increase classification accuracy for some bat species and decrease accuracy for others, but a detailed understanding of how clutter impacts the recording and identification of echolocation calls remains elusive. To clarify this, we experimentally investigated how two measures of clutter (i.e., total basal area and number of stems of simulated woody growth, as well as recording angle) affected the recording and classification of a synthesized echolocation signal under controlled conditions in an anechoic chamber. Recording angle (i.e., receiver position relative to emitter) significantly influenced the probability of correct classification and differed significantly for many of the call parameters measured. The probability of recording echo pulses was also a function of clutter but only for the detector angle at 0° from the emitter that could receive deflected pulses. Overall, the two clutter metrics were overshadowed by proximity and angle of the receiver to the sound source but some deviations from the synthesized call in terms of maximum, minimum, and mean frequency parameters were observed. Results from our work may aid efforts to better understand underlying environmental conditions that produce false-positive and -negative identifications for bat species of interest and how this could be used to adjust survey accuracy estimates. Our results also help pave the way for future research into the development of acoustic lure technology by exploring the effects of environmental clutter on ultrasound transmission.

Acoustics↗
USGS2006

What's weathering? Mineralogy and field leach studies in mine waste, Leadville and Montezuma mining districts, Colorado

Weathering is important in the development of rock fabrics that control porosity in mine-waste materials, and in turn, porosity affects metal transport through and from mine-waste piles into watersheds. Mine-waste piles are dynamic physical and chemical systems as evidenced by remnant Fe-oxide boxwork structures after sulfide minerals, development of alteration rinds and etch pits on grains, and precipitation of secondary minerals under low temperature conditions. These microscale changes in the mine-waste materials are the result of partial to total dissolution of sulfide and other minerals. Mine-waste materials from the Dinero, Lower Chatauqua, and Saints John sites, Leadville and Montezuma mining districts, Colorado, exhibit rock fabrics that indicate that weathering products, e.g., Fe oxyhydroxides, jarosite, and clays, have been transported in suspension through the waste piles and deposited in voids and as coatings on rock fragments. Microscale characterization of weathered, partially dissolved minerals lends insight into the source of leachable metals in these mine-waste sites. Mineralogic studies show that galena in the Lower Chatauqua waste is enriched in Ag. Qualitative and semiquantitative microanalysis of weathered, altered galena grains from all three sites show that the Ag-bearing galena is more susceptible to dissolution. It is not surprising, then, that solutions experimentally leached from Lower Chatauqua waste are higher in Pb (2310 ppb) compared to leachates from the Dinero (31 ppb) and Saints John (1360 ppb) wastes. The mobility of metals is increased at acidic pH. Using the USGS Field Leach Test protocol, leachate derived from the Dinero waste has a pH of 3 and high concentrations of Al (443 ppb), Fe (441 ppb), and Zn (7970 ppb). Leachate from Sts. John tailings has a pH about 4 and high concentrations of Mn (1520 ppb), Zn (2240 ppb), and Pb (1360 ppb). Leachate from the Lower Chatauqua waste has an intermediate pH of 5, but in addition to the high Pb level already mentioned, it contains high levels of K (1.9 ppm), Mn (6720 ppb), and Zn (1550 ppb). The high concentration of metals, despite the intermediate pH of the leachate, may be explained by acidic microenvironments that exist at the surfaces of sulfide minerals, where sulfur-and iron-oxidizing microbes may flourish. It is at the reactive mineral-oxygen-water interface where metals are released and low-pH sulfate precipitates such as jarosite-beudantite form.

Colorado↗
USGS1985

Experimental studies in natural groundwater-recharge dynamics: The analysis of observed recharge events

The amounts and time distribution of groundwater recharge from precipitation over an approximately 19-month period were investigated at two instrumented sites in south-central Kansas. Precipitation and evapotranspiration sequences, soil-moisture profiles and storage changes, water fluxes in the unsaturated zone and hydraulic gradients in the saturated zone at various depths, soil temperatures, water-table hydrographs, and water-level changes in nearby wells clearly depict the recharge process. Antecedent moisture conditions and the thickness and nature of the unsaturated zone were found to be the major factors affecting recharge. Although the two instrumented sites are located in sand-dune environments in areas characterized by shallow water table and subhumid continental climate, a significant difference was observed in the estimated effective recharge. The estimates ranged from less than 2.5 to approximately 154 mm at the two sites from February to June 1983. The main reasons for this large difference in recharge estimates were the greater thickness of the unsaturated zone and the lower moisture content in that zone resulting from lower precipitation and higher potential evapotranspiration for one of the sites. Effective recharge took place only during late winter and spring. No summer or fall recharge was observed at either site during the observation period of this study.

Kansas↗
USGS1972

Prospects for earthquake prediction and control

The San Andreas fault is viewed, according to the concepts of seafloor spreading and plate tectonics, as a transform fault that separates the Pacific and North American plates and along which relative movements of 2 to 6 cm/year have been taking place. The resulting strain can be released by creep, by earthquakes of moderate size, or (as near San Francisco and Los Angeles) by great earthquakes. Microearthquakes, as mapped by a dense seismograph network in central California, generally coincide with zones of the San Andreas fault system that are creeping. Microearthquakes are few and scattered in zones where elastic energy is being stored. Changes in the rate of strain, as recorded by tiltmeter arrays, have been observed before several earthquakes of about magnitude 4. Changes in fluid pressure may control timing of seismic activity and make it possible to control natural earthquakes by controlling variations in fluid pressure in fault zones. An experiment in earthquake control is underway at the Rangely oil field in Colorado, where the rates of fluid injection and withdrawal in experimental wells are being controlled.

California↗
USGS2019

The effectiveness of non-native fish removal techniques in freshwater ecosystems: a systematic review

In aquatic systems, biological invasions can result in adverse ecological effects. Management techniques available for non-native fish removal programs (including eradication and population size control) vary widely, but include chemicals, harvest regimes, physical removal, or biological control. For management agencies, deciding on what non-native fish removal program to use has been challenging because there is little reliable information about the relative effectiveness of these measures in controlling or eradicating non-native fish. We conducted a systematic review, including a critical appraisal of study validity, to assess the effectiveness of different non-native fish removal methods, and to identify the factors that influence the overall success rate of each type of method. We found 95 relevant studies, generating 158 data sets. The evidence base was dominated by poorly documented studies with inadequate experimental designs (76% of removal projects). When the management goal was non-native fish eradication, chemical treatments were relatively successful (antimycin 75%; rotenone 89%) compared to other interventions. Electrofishing and passive removal measure studies indicated successful eradication was possible (58% each respectively) but required intensive effort and multiple treatments over a number of years. Of these studies with sufficient information, electrofishing had the highest success for population size control (56% of data sets). Overall, inadequate data quality and completeness severely limited our ability to make strong conclusions about the relationships between non-native fish abundance and different methods of eradication and population control, and the factors influencing the overall success rate of each method. Our review highlights that there is considerable scope for improving our evaluations of non-native fish removal methods. It is recommended that programs should have explicitly stated objectives, better data reporting, and study designs that (when possible and appropriate) incorporate replicated and controlled investigations with rigorous, long-term quantitative monitoring. Future research on the effectiveness of non-native fish removal methods should focus on: (1) the efficacy of existing or potentially new removal measures in larger, more complex environments; (2) a broader range of removal measures in general, and (3) phenotypic characteristics of individual fish within a population that fail to be eradicated or controlled.

Environmental Reviews↗
USGS2023

A nitrifier-enriched microbial community contributes to the degradation of environmental DNA

Environmental DNA (eDNA) surveys are a promising alternative to traditional monitoring of invasive species, rare species, and biodiversity. Detecting organism-specific eDNA reduces the need to collect physical specimens for population estimates, and the high sensitivity of eDNA assays may improve detection of rare or cryptic species. However, correlating estimated concentrations of eDNA with species abundance can be difficult due to the many abiotic and biotic factors that influence eDNA persistence and degradation. Here, we assessed the impact of a nitrifier-enriched microbial (NEM) community on the persistence and degradation of Hypophthalmichthys molitrix (silver carp) milt eDNA using experimental aquatic mesocosms and a quantitative PCR approach. The NEM community was cultured from combined sediment and water samples collected from a golf course pond in Columbia, Missouri (USA), and experiments were conducted in the dark at 22°C. We found that the NEM community transformed organic nitrogen from silver carp milt to measurable amounts of nitrate, both in the presence and absence of ammonia nitrogen. Additionally, regardless of ammonia availability, milt eDNA followed a one-phase exponential decay pattern after an initial 24-h plateau in the presence of the NEM community. However, milt eDNA had a shorter half-life (12.5 h) in the absence of exogenous ammonia compared to when ammonia was present (15 h). In sterile mesocosms, eDNA was stable during the 72-h experiment. Together, these results suggest that the presence of microorganisms is necessary for short-term degradation of eDNA. Furthermore, nitrifying microbial communities, which are ubiquitous in most soil and water environments, could limit eDNA persistence in the environment. Understanding the contributions of environmental microbial communities will allow more confidence in sampling design and eDNA result interpretations for biodiversity management applications.

Environmental DNA↗
USGS2020

Climate’s cascading effects on disease, predation, and hatching success in Anaxyrus canorus, the threatened Yosemite toad

The U.S. Fish and Wildlife Service listed Anaxyrus canorus , the Yosemite toad, as federally threatened in 2014 based upon reported population declines and vulnerability to global-change factors. A. canorus lives only in California’s central Sierra Nevada at medium to sub-alpine elevations. Lands throughout its range are protected from development, but climate and other global-change factors potentially can limit populations. A. canorus reproduces in ultra-shallow wetlands that typically hydrate seasonally via melting of the winter snowpack. Lesser snowpacks in drier years can render wetland water volumes and hydroperiods insufficient to allow for successful breeding and reproduction. Additionally, breeding and embryogenesis occur very soon after wetlands thaw when overnight temperatures can be below freezing. Diseases, such as chytridiomycosis, which recently decimated regional populations of ranid species, also might cause declines of A. canorus populations. However, reported studies focused on whether climate interacts with any pathogens to affect fitness in A. canorus have been scarce. We investigated effects of these factors on A. canorus near Tioga Pass from 1996 to 2001. We found breeding subpopulations were distributed widely but inconsistently among potentially suitable wetlands and frequently consisted of small numbers of adults. We occasionally observed small but not alarming numbers of dead adults at breeding sites. In contrast, embryo mortality often was notably high, with the majority of embryos dead in some egg masses while mortality among coincidental Pseudacris regilla (Pacific treefrog) embryos in deeper water was lower. After sampling and experimentation, we concluded that freezing killed A. canorus embryos, especially near the tops of egg masses, which enabled Saprolegnia diclina (a water mold [Oomycota]) to infect and then spread through egg masses and kill more embryos, often in conjunction with predatory flatworms ( Turbellaria spp.). We also concluded exposure to ultraviolet-B radiation did not play a role. Based upon our assessments of daily minimum temperatures recorded around snow-off during years before and after our field study, the freezing potential we observed at field sites during embryogenesis might have been commonplace beyond the years of our field study. However, interactions among snow quantity, the timing of snow-off, and coincidental air temperatures that determine such freezing potential make projections of future conditions highly uncertain, despite overall warming trends. Our results describe important effects from ongoing threats to the fitness and abundance of A. canorus via reduced reproduction success and demonstrate how climate conditions can exacerbate effects from pathogens to threaten the persistence of amphibian populations.

California↗
USGS2013

Laboratory-derived temperature preference and effect on the feeding rate and survival of juvenile Hemimysis anomala

Hemimysis anomala is a warm-water mysid that invaded the Great Lakes region in 2006 and has since rapidly spread throughout the basin. We conducted three laboratory experiments to better define the temperature preference, tolerance limits, and temperature effects on feeding rates of juvenile Hemimysis, using individuals acclimated to mid (16 °C) and upper (22 °C) preferred temperature values previously reported for the species. For temperature preference, we fit a two-parameter Gaussian (μ, σ) function to the experimental data, and found that the peak values (μ, interpreted as the preference temperature) were 22.0 °C (SE 0.25) when acclimated to 16 and 21.9 °C (SE 0.38) when acclimated to 22 °C, with the σ-values of the curves at 2.6 and 2.5 °C, respectively. No mysids were observed in temperatures below 10 or above 28 °C in these preference experiments. In short-term tolerance experiments for temperatures between 4 and 32 °C, all mysids died within 8 h at 30.2 °C for 16 °C acclimated mysids, and at 31.8 °C for 22 °C acclimated mysids. No lower lethal limit was found. Feeding rates increased with temperature from an average of 4 Bosmina eaten per hour at 5 °C to 19 Bosmina eaten per hour at 27 °C. The results of our experiments indicate an optimal temperature for Hemimysis between 21 and 27 °C, which corresponds with temperatures during periods of high population growth in the field. These results contribute a better understanding of this species' biological response to temperature that will help guide field studies and inform bioenergetics modeling.

New York↗
USGS2011

Evaluating the potential for stock size to limit recruitment in largemouth bass

Compensatory changes in juvenile survival allow fish stocks to maintain relatively constant recruitment across a wide range of stock sizes (and levels of fishing), but few studies have experimentally explored recruitment compensation in fish populations. We evaluated the potential for recruitment compensation in largemouth bass Micropterus salmoides by stocking six 0.4-ha hatchery ponds with adult densities ranging from 6 to 40 fish over 2 years. Ponds were drained in October each year, and the age-0 fish densities were used as a measure of recruitment. We found no relationship between stock abundance and recruitment; ponds with low adult densities produced nearly as many recruits as the higher-density ponds in some cases. Both prey abundance and the growth of age-0 largemouth bass declined with age-0 fish density. Recruit abundance was highly variable both within and among the adult density groups, and thus we were unable to identify a clear stock–recruit relationship for largemouth bass. Our results indicate that reducing the number of effective spawners via angling practices would not reduce recruitment over a relatively large range in stock size.

Transactions of the American Fisheries Society↗
USGS2025

A Cftr-independent, Ano1-rich seawater-adaptive ionocyte in sea lamprey gills

All ionoregulating marine fishes examined to date utilize seawater-type ionocytes expressing the apical Cl- channel, cystic fibrosis transmembrane conductance regulator (Cftr) to secrete Cl − . We performed transcriptomic, molecular, and functional studies to identify Cl − transporters in the seawater-type ionocytes of sea lamprey ( Petromyzon marinus ). Gill cftr expression was minimal or undetectable in larvae and post-metamorphic juveniles. We identified other Cl − transporters highly expressed in the gills and/or upregulated following metamorphosis and further investigated two candidates that stood out in our analysis, a Ca 2+ -activated Cl − channel, anoctamin 1 ( ano1 ), and the Clc chloride channel family member 2 ( clcn2 ). Of these, ano1 was expressed 10-100 times more than clcn2 in the gills; moreover, ano1 was upregulated during seawater acclimation, while clcn2 was not. Using an antibody raised against sea lamprey Ano1, we did not detect Ano1 in the gills of larvae, found elevated levels in juveniles and observed a 4-fold increase in juveniles after seawater acclimation. Ano1 was localized to seawater-type branchial ionocytes but, surprisingly, was localized to the basolateral membrane. In vivo pharmacological inhibition experiments demonstrated that a DIDS-sensitive mechanism was critical to the maintenance of osmoregulatory homeostasis in seawater- but not freshwater-acclimated sea lamprey. Taken together, our results provide evidence of a Cftr-independent mechanism for branchial Cl − secretion in sea lamprey that leverages Ano1-expressing ionocytes. Once further characterized, the Cftr-independent, Ano1-rich ionocytes of sea lamprey could reveal novel strategies for branchial Cl − secretion, whether by Ano1 or some other Cl − transporter, not previously known in ionoregulating marine organisms.

Journal of Experimental Biology↗
USGS2008

Introduced mammalian predators induce behavioural changes in parental care in an endemic New Zealand bird

The introduction of predatory mammals to oceanic islands has led to the extension of many birds. Although introduced predators should favour changes that reduce predation risk in surviving bird species, the ability of island birds to respond to such novel changes remains unstudied. We tested whether novel predation risk imposed by introduced mammalian predators has altered the parental behaviour of the endemic New Zealand bellbird (Anthomis melanura). We examined parental behaviour of billbnirds at three woodlands sites in New Zealand that differed in predation risk: 1) a mainland site with exotic predators present (high predation risk), 2) a mainland site with exotic predators experimentally removed (low risk recently) and, 3) an off-shore island where exotic predators were never introduced (low risk always). We also compared parental behavior of bellbirds with two closely related Tasmanian honeyeaters (Phylidonyris spp) that evolved with native nest predators (high risk always). Increased nest predation risk has been postulated to favour reduced parental activity, and we tested whether island bellbirds responded to variation in predation risk. We found that females spent more time on the nest per incubating bout with increased risk of predation, a strategy that minimised activity at the nest during incubation. Parental activity during the nestling period, measured as number of feeding visits/hr, also decreased with increasing nest predation risk across sites, and was lowest among the honeyeaters in Tasmania that evolved with native predators. These results demonstrates that some island birds are able to respond to increased risk of predation by novel predators in ways that appear adaptive. We suggest that conservation efforts may be more effective if they take advantage of the ability of island birds to respond to novel predators, especially when the elimination of exotic predators is not possible.

PLoS ONE↗
USGS1989

Liquid-vapor relations for the system NaCl-H2O: Summary of the P-T- x surface from 300° to 500°C

Experimental data on the vapor-liquid equilibrium relations for the system NaCl-H 2 O were compiled and compared in order to provide an improved estimate of the P-T-x surface between 300 ° to 500 ° C, a range for which the system changes from subcritical to critical behavior. Data for the three-phase curve (halite + liquid + vapor) and the NaCl-H 2 O critical curve were evaluated, and the best fits for these extrema then were used to guide selection of best fit for isothermal plots for the vapor-liquid region in-between. Smoothing was carried out in an iterative procedure by replotting the best-fit data as isobars and then as isopleths, until an internally consistent set of data was obtained. The results are presented in table form that will have application to theoretical modelling and to the understanding of two-phase behavior in saline geothermal systems.

American Journal of Science↗
USGS2013

Influence of dissolved organic matter character on mercury incorporation by planktonic organisms: an experimental study using oligotrophic water from Patagonian lakes

Ligands present in dissolved organic matter (DOM) form complexes with inorganic divalent mercury (Hg 2+ ) affecting its bioavailability in pelagic food webs. This investigation addresses the influence of a natural gradient of DOM present in Patagonian lakes on the bioaccumulation of Hg 2+ (the prevailing mercury species in the water column of these lakes) by the algae Cryptomonas erosa and the zooplankters Brachionus calyciflorus and Boeckella antiqua. Hg 2+ accumulation was studied through laboratory experiments using natural water of four oligotrophic Patagonian lakes amended with 197 Hg 2+ . The bioavailability of Hg 2+ was affected by the concentration and character of DOM. The entrance of Hg 2+ into pelagic food webs occurs mostly through passive and active accumulation. The incorporation of Hg 2+ by Cryptomonas, up to 27% of the Hg 2+ amended, was found to be rapid and dominated by passive adsorption, and was greatest when low molecular weight compounds with protein-like or small phenolic signatures prevailed in the DOM. Conversely, high molecular weight compounds with a humic or fulvic signature kept Hg 2+ in the dissolved phase, resulting in the lowest Hg 2+ accumulation in this algae. In Brachionus and Boeckella the direct incorporation of Hg from the aqueous phase was up to 3% of the Hg 2+ amended. The dietary incorporation of Hg 2+ by Boeckella exceeded the direct absorption of this metal in natural water, and was remarkably similar to the Hg 2+ adsorbed in their prey. Overall, DOM concentration and character affected the adsorption of Hg 2+ by algae through competitive binding, while the incorporation of Hg 2+ into the zooplankton was dominated by trophic or dietary transfer.

Patagonia↗
USGS2006

Stress does not inhibit induced vitellogenesis in juvenile rainbow trout

Vitellogenin (Vtg) is a widely used biomarker for xenoestrogen exposure in male fishes. In female fishes Vtg can be negatively affected by stress independent of declines in estrogen. However, few data are available on the effect of stress in male fish abnormally producing Vtg, such as when exposed to xenoestrogens. The objective for these studies was to determine the effects of stress on fish forced to produce Vtg. Three weeks prior to the experiment immature juvenile rainbow trout, Oncorhynchus mykiss, were acclimated to the experimental tanks and fed a maintenance ration. We induced Vtg synthesis by injecting 17??-estradiol (E2) 7 days prior to experimentation. Treatments in duplicate tanks were: (1) no stressor; (2) stressor; (3) E 2; (4) E2 and stressor. Plasma was collected at time = 0 for baseline measurements from eight fish per tank and Vtg was significantly elevated in treated fish compared to uninjected controls. Water was drained from the stressor tanks then refilled to a level that just covered the backs of the fish. Eight fish were sampled again at 4 and 9 h, and 1, 7, and 14 days of continuous stress. Stressor tanks were refilled with water to pre-stress levels and the fish were sampled after another 2 weeks. Cortisol was significantly elevated from the unstressed fish at 4 h; however, plasma Vtg in the E 2-stimulated fish was not affected by the stressor at any timepoint. These results indicate that fish capture procedures employed in the field or caging experiments likely do not lead to false negative results when plasma Vtg is used as a biomarker for xenoestrogen exposure. It also suggests that the energetic load induced by stress is insufficient to cause a reduction in Vtg, during a continuous E2 administration, at least within the timepoints examined in this study. ?? 2006 Springer Science+Business Media, Inc.

Environmental Biology of Fishes↗