Prior thermal acclimation gives White Sturgeon a fin up dealing with low oxygen.

Assessing how at-risk species respond to co-occurring stressors is critical for predicting climate change vulnerability. In this study, we characterized how young-of-the-year White Sturgeon () cope with warming and low oxygen (hypoxia) and investigated whether prior exposure to one stressor may improve the tolerance to a subsequent stressor through "cross-tolerance". Fish were acclimated to five temperatures within their natural range (14-22°C) for one month prior to assessment of thermal tolerance (critical thermal maxima, CTmax) and hypoxia tolerance (incipient lethal oxygen saturation, ILOS; tested at 20°C).

Insights from a year of field deployments inform the conservation of an endangered estuarine fish.

Freshwater fishes are increasingly facing extinction. Some species will require conservation intervention such as habitat restoration and/or population supplementation through mass-release of hatchery fish. In California, USA, a number of conservation strategies are underway to increase abundance of the endangered Delta Smelt (); however, it is unclear how different estuarine conditions influence hatchery fish.

Physiological response of longfin smelt to changing temperatures and turbidities.

Coastal estuaries globally, including the San Francisco Estuary (SFE), are experiencing significant degradation, often resulting in fisheries collapses. The SFE has undergone profound modifications due to population growth, industrialization, urbanization and increasing water exports for human use. These changes have significantly altered the aquatic ecosystem, favouring invasive species and becoming less hospitable to native species such as the longfin smelt ().

Impacts of ash-induced environmental alkalinization on fish physiology, and their implications to wildfire-scarred watersheds.

Changes in land use, a warming climate and increased drought have amplified wildfire frequency and magnitude globally. Subsequent rainfall in wildfire-scarred watersheds washes ash into aquatic systems, increasing water pH and exposing organisms to environmental alkalinization. In this study, 15 or 20 °C-acclimated Chinook salmon (Oncorhynchus tshawytscha) yearlings were exposed to an environmentally-relevant ash concentration (0.

Effects of low temperature on growth and metabolism of larval green sturgeon (Acipenser medirostris) across early ontogeny.

Southern Distinct Population Segment (sDPS) green sturgeon spawn solely in one stretch of the Sacramento River in California. Management of this spawning habitat is complicated by cold water temperature requirements for the conservation of winter-run Chinook salmon. This study assessed whether low incubation and rearing temperatures resulted in carryover effects across embryo to early juvenile life stages on scaling relationships in growth and metabolism in northern DPS green sturgeon used as a proxy for sDPS green sturgeon.

Effects of acclimation temperature and feed restriction on the metabolic performance of green sturgeon.

Green sturgeon () are an anadromous threatened species of sturgeon found along the Pacific coast of North America. The southern distinct population segment only spawns in the Sacramento River and is exposed to water temperatures kept artificially cold for the conservation and management of winter-run Chinook salmon (). Past research has demonstrated costs of cold-water rearing including reduced growth rates, condition and survivorship of juvenile green sturgeon.

Smaller body size under warming is not due to gill-oxygen limitation in a cold-water salmonid.

Declining body size in fishes and other aquatic ectotherms associated with anthropogenic climate warming has significant implications for future fisheries yields, stock assessments and aquatic ecosystem stability. One proposed mechanism seeking to explain such body-size reductions, known as the gill oxygen limitation (GOL) hypothesis, has recently been used to model future impacts of climate warming on fisheries but has not been robustly empirically tested. We used brook trout (Salvelinus fontinalis), a fast-growing, cold-water salmonid species of broad economic, conservation and ecological value, to examine the GOL hypothesis in a long-term experiment quantifying effects of temperature on growth, resting metabolic rate (RMR), maximum metabolic rate (MMR) and gill surface area (GSA).

Effects of incubation temperature on the upper thermal tolerance of the imperiled longfin smelt ().

Upper thermal limits in many fish species are limited, in part, by the heart's ability to meet increased oxygen demand during high temperatures. Cardiac plasticity induced by developmental temperatures can therefore influence thermal tolerance. Here, we determined how incubation temperatures during the embryonic stage influence cardiac performance across temperatures during the sensitive larval stage of the imperiled longfin smelt.

Prey ration, temperature, and predator species influence digestion rates of prey DNA inferred from qPCR and metabarcoding.

Diet analysis is a vital tool for understanding trophic interactions and is frequently used to inform conservation and management. Molecular approaches can identify diet items that are impossible to distinguish using more traditional visual-based methods. Yet, our understanding of how different variables, such as predator species or prey ration size, influence molecular diet analysis is still incomplete.

Effects of turbidity, temperature and predation cue on the stress response of juvenile delta smelt.

The San Francisco Estuary (SFE) is one of the most degraded ecosystems in the United States, and organisms that inhabit it are exposed to a suite of environmental stressors. The delta smelt (), a small semi-anadromous fish endemic to the SFE and considered an indicator species, is close to extinction in the wild. The goal of this study was to investigate how environmental alterations to the SFE, such as reductions in turbidities, higher temperatures and increased prevalence of invasive predators affect the physiology and stress response of juvenile delta smelt.

Bifenthrin, a Ubiquitous Contaminant, Impairs the Development and Behavior of the Threatened Longfin Smelt during Early Life Stages.

The Longfin Smelt () population in the San Franscisco Bay/Sacramento-San Joaquin Delta (Bay-Delta) has declined to ∼1% of its pre-1980s abundance and, as a result, is listed as threatened under the California Endangered Species Act. The reasons for this decline are multiple and complex, including the impacts of contaminants. Because the spawning and rearing seasons of Longfin Smelt coincide with the rainy season, during which concentrations of contaminants increase due to runoff, we hypothesized that early life stages may be particularly affected by those contaminants.

Intraspecific variation among Chinook Salmon populations indicates physiological adaptation to local environmental conditions.

Understanding interpopulation variation is important to predicting species responses to climate change. Recent research has revealed interpopulation variation among several species of Pacific salmonids; however, the environmental drivers of population differences remain elusive. We tested for local adaptation and countergradient variation by assessing interpopulation variation among six populations of fall-run Chinook Salmon from the western United States.

Captive-reared Delta Smelt (Hypomesus transpacificus) exhibit high survival in natural conditions using in situ enclosures.

Conservation of endangered fishes commonly includes captive breeding, applied research, and management. Since 1996, a captive breeding program has existed for the federally threatened and California endangered Delta Smelt Hypomesus transpacificus, an osmerid fish endemic to the upper San Francisco Estuary. Although this program serves as a captive refuge population, with experimental releases being initiated to supplement the wild population, it was uncertain how individuals would survive, feed, and maintain condition outside hatchery conditions.

Increasing stability of a native freshwater fish assemblage following flow rehabilitation.

Stream restorations are increasingly critical for managing and recovering freshwater biodiversity in human-dominated landscapes. However, few studies have quantified how rehabilitative actions promulgate through aquatic communities over decades. Here, a long-term dataset is analyzed for fish assemblage change, incorporating data pre- and post-restoration periods, and testing the extent to which native assemblage stability has increased over time.

The ecological relevance of critical thermal maxima methodology for fishes.

Critical thermal maxima methodology (CTM) has been used to infer acute upper thermal tolerance in fishes since the 1950s, yet its ecological relevance remains debated. In this study, the authors synthesize evidence to identify methodological concerns and common misconceptions that have limited the interpretation of critical thermal maximum (CT ; value for an individual fish during one trial) in ecological and evolutionary studies of fishes. They identified limitations of, and opportunities for, using CT as a metric in experiments, focusing on rates of thermal ramping, acclimation regimes, thermal safety margins, methodological endpoints, links to performance traits and repeatability.

The effect of temperature on specific dynamic action of juvenile fall-run Chinook salmon, .

Juvenile fall-run Chinook salmon () in the Sacramento-San Joaquin River Basin experience temporally and spatially heterogenous temperature regimes, between cool upper tributaries and the warm channelized Delta, during freshwater rearing and outmigration. Limited water resources necessitate human management of dam releases, allowing temperature modifications. The objective of this study was to examine the effect of temperature on specific dynamic action (SDA), or the metabolic cost associated with feeding and digestion, which is thought to represent a substantial portion of fish energy budgets.

Characterizing the stress response in juvenile Delta smelt exposed to multiple stressors.

The Delta Smelt (Hypomesus transpacificus), once an abundant fish endemic to the Sacramento-San Joaquin Estuary, is now on the brink of extinction. Due to the high sensitivity of this species, knowledge of their stress response will be vital to their future survival and sustainability. Understanding the magnitude and kinetics of cortisol induction in Delta Smelt will provide valuable information when interpreting the degree of environmentally relevant stressors, such as warming and predator exposure.

Growth, osmoregulation and ionoregulation of longfin smelt () yolk-sac larvae at different salinities.

Longfin smelt () is a threatened anadromous fish species that spawns in freshwater to moderately brackish (i.e. 5-10 ppt) reaches of the upper San Francisco Estuary and has declined to ~1% of its pre-1980s abundances.

Understanding risks and consequences of pathogen infections on the physiological performance of outmigrating Chinook salmon.

The greatest concentration of at-risk anadromous salmonids is found in California (USA)-the populations that have been negatively impacted by the degradation of freshwater ecosystems. While climate-driven environmental changes threaten salmonids directly, they also change the life cycle dynamics and geographic distribution of pathogens, their resulting host-pathogen interactions and potential for disease progression. Recent studies have established the correlation between pathogen detection and salmonid smolt mortality during their migration to the ocean.

Epidermal cell cultures from white and green sturgeon (Acipenser transmontanus and medirostris): Expression of TGM1-like transglutaminases and CYP4501A.

Using a system optimized for propagating human keratinocytes, culture of skin samples from white and green sturgeons generated epithelial cells capable of making cross-linked protein envelopes. Two distinct forms of TGM1-like mRNA were molecularly cloned from the cells of white sturgeon and detected in green sturgeon cells, accounting for their cellular envelope forming ability. The protein translated from each displayed a cluster of cysteine residues resembling the membrane anchorage region expressed in epidermal cells of teleosts and tetrapods.

Swimming behavior of emigrating Chinook Salmon smolts.

Swimming behavior of Chinook Salmon (Oncorhynchus tshawytscha) smolts affects transit time, route selection and survival in complex aquatic ecosystems. Behavior quantified at the river reach and junction scale is of particular importance for route selection and predator avoidance, though few studies have developed field-based approaches for quantifying swimming behavior of juvenile migratory fishes at this fine spatial scale. Two-dimensional acoustic fish telemetry at a river junction was combined with a three-dimensional hydrodynamic model to estimate in situ emigration swimming behavior of federally-threatened juvenile Chinook salmon smolts.

Biogeochemical processes create distinct isotopic fingerprints to track floodplain rearing of juvenile salmon.

Floodplains represent critical nursery habitats for a variety of fish species due to their highly productive food webs, yet few tools exist to quantify the extent to which these habitats contribute to ecosystem-level production. Here we conducted a large-scale field experiment to characterize differences in food web composition and stable isotopes (δ¹³C, δ¹⁵N, δ³⁴S) for salmon rearing on a large floodplain and adjacent river in the Central Valley, California, USA. The study covered variable hydrologic conditions including flooding (1999, 2017), average (2016), and drought (2012-2015).

Exposure to permethrin or chlorpyrifos causes differential dose- and time-dependent behavioral effects at early larval stages of an endangered teleost species.

Pyrethroid and organophosphate pesticides are two of the most commonly used classes of insecticide worldwide. At sublethal concentrations, permethrin (a pyrethroid) and chlorpyrifos (an organophosphate) impact behavior in model fish species. We investigated behavioral effects of environmentally relevant concentrations of permethrin or chlorpyrifos on early larval delta smelt , a Critically Endangered teleost species endemic to the San Francisco Bay Delta, California, USA.