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Conservation aquaculture has prevented extirpation of Upper Columbia River white sturgeon Acipenser transmontanus, but uncertainty remains on how hatchery-origin fish move between habitats located within Canada and the United States. We describe how core and home ranges of sturgeon varied by environmental (country, season) and biological (age, sex, size) factors and determined residence at important habitats. Core range represented areas where individuals spent the majority of their time, while home range represented most areas occupied. Fidelity to specific habitats was high, with home ranges averaging 10 km2 and 50% of individuals occupied the same core range across their entire detection period. Only 12% of individuals had home ranges encompassing both countries. Core and home ranges were larger during the summer compared to winter and larger within the United States compared to Canada. Larger (>120 cm) sturgeon had increased core and home ranges. We documented spawning capable hatchery-origin males and confirmed their residence at spawning sites when spawning was detected. Results improve our understanding of species biology and directly inform adaptive management of population recovery. [ABSTRACT FROM AUTHOR]

ABSTRACT Understanding the distribution and habitat use of endangered species is essential for conservation efforts. Environmental DNA (eDNA) analysis has become a more common approach to defining species habitat occupancy through identification of residual DNA in water samples and has potential to detect populations that are in low abundance or use habitats over a large geographical range. Here, we optimized an eDNA protocol to detect the presence of the endangered white sturgeon (Acipenser transmontanus). We implemented lab‐based experiments to understand the sensitivity and persistence of white sturgeon eDNA and then applied these methods to habitats with known white sturgeon abundances categorized as high, low, or not present. Using quantitative PCR (qPCR) and a modified StrAci1N‐flap primer set, white sturgeon eDNA was detected in water collected from tanks holding white sturgeon down to a dilution of 10,000× (estimated eDNA concentration of 0.00035 μg/L—0.00176 μg/L). Following the removal of white sturgeon from the tanks, the eDNA signal decreased with time but could be detected for up to 7 days. In the field, all sites with high abundances of white sturgeon returned positive eDNA detections. We did not detect white sturgeon eDNA at sites with low abundance or in areas where they were not expected to be present. Results from this work further advance our interpretation of eDNA from wild populations and provide a noninvasive method to advance recovery efforts by identifying species presence in areas of suspected use or to guide additional inventory efforts.

Acipenserid herpesvirus 2 (AciHV-2) is a large double-stranded DNA virus in the family Alloherpesviridae that causes catastrophic outbreaks in young naive white sturgeon (Acipenser transmontanus) populations, with mortalities of up to 80%. Survivors of these infections are suspected to remain latently infected. The grampositive zoonotic bacterium Streptococcus iniae is another important sturgeon pathogen that causes severe myositis and up to 50% mortality during natural outbreaks. Throughout the last decade, co-infections of AciHV-2 and S. iniae have been reported in cultured white sturgeon in California resulting in severe presentations of piscine streptococcosis. This phenomenon of herpesvirus and streptococcus co-infection appears to span multiple taxa since in humans, it is recognized that a Human herpesvirus 3 infection (VZV) is a negative prognostic indicator for pediatric Invasive Group A Streptococcal infections (IGASI). While a decrease in humoral immunity caused by VZV has been hypothesized as a potentially important factor in IGASI cases, no natural animal model exists to study this process. Moreover, no studies have investigated these reported coinfections in white sturgeon. Therefore, the goal of this study was to investigate the effects of a recent AciHV-2 infection on the outcome of a subsequent S. iniae challenge in white sturgeon fingerlings. When fish were infected with 108 colony forming units (CFU) of S. iniae intramuscularly (IM), a statistically significant decrease in survival of 41% was detected in the co-infection group compared to the S. iniae group (p-value < 0.001). This difference was not observed when fish were infected with 106 CFU of S. iniae IM. At this lower infection dose, however, a statistically significant downregulation of tnfa was observed in the spleen of fish in the co-infection group compared to the S. iniae group (p-value = 0.0098). Analysis of serum from survivors revealed a statistically significant reduction in anti-S. iniae serum IgM and serum serotransferrin in fish from the co-infection group compared to the S. iniae group (p-value = 0.0134 and p-value = 0.0183, respectively). Further studies are indicated to determine what interactions lead to the decreased production of pathogen-specific IgM, serotransferrin, and TNFa in the host. [ABSTRACT FROM AUTHOR]

Green sturgeon (Acipenser medirostris) and white sturgeon (A. transmontanus) are closely related, sympatric species that inhabit the San Francisco estuary. Green sturgeon have a more marine life history but both species spawn in the Sacramento River and reside for some duration in San Francisco Bay. These sturgeons are of conservation concern, yet little is known about their dietary competition when they overlap in space and time. To examine evidence of dietary differentiation, we collected whole blood and blood plasma from 26 green sturgeon and 35 white sturgeon in San Francisco Bay. Using carbon and nitrogen stable isotope analyses, we compared their relative trophic levels and foraging locations along the freshwater to marine gradient. Sampling blood plasma and whole blood allowed comparison of dietary integration over shorter and longer time scales, respectively. Plasma and whole blood δ13C values confirmed green sturgeon had more marine dietary sources than white sturgeon. Plasma δ15N values revealed white sturgeon fed at lower trophic levels than green sturgeon recently, however, whole blood δ15N values demonstrated the two species fed at the same trophic level over longer time scales. Larger individuals of both species had higher δ13C values than smaller individuals, reflecting more marine food sources in adulthood. Length did not affect δ15N values of either species. Isotope analyses supported the more marine life history of green than white sturgeon and potentially highlight a temporary trophic differentiation of diet between species during and preceding the overlapping life stage in San Francisco Bay. [ABSTRACT FROM AUTHOR]

Five metal mixture dose–response models were used to predict the toxicity of porewater to young sturgeon at areas of interest in the Upper Columbia River (WA, USA/BC, Canada) and to evaluate these models as tools for risk assessments. Dose components of metal mixture models included exposure to free metal ion activities or metal accumulation by biotic ligands or humic acid, and links of dose to response used logistic equations, independent joint action equations, or additive toxicity functions. Laboratory bioassay studies of single metal exposures to juvenile sturgeon, porewater collected in situ in the fast‐flowing Upper Columbia River, and metal mixture models were used to evaluate toxicity. The five metal mixture models were very similar in their predictions of adverse response of juvenile sturgeon and in identifying copper (Cu) as the metal responsible for the most toxic conditions. Although the modes of toxic action and the 20% effective concentration values were different among the dose models, predictions of adverse response were consistent among models because all doses were tied to the same biological responses. All models indicated that 56% ± 5% of 122 porewater samples were predicted to have <20% adverse response, 25% ± 5% of samples were predicted to have 20% to 80% adverse response, and 20% ± 4% were predicted to have >80% adverse response in juvenile sturgeon. The approach of combining bioassay toxicity data, compositions of field porewater, and metal mixture models to predict lack of growth and survival of aquatic organisms due to metal toxicity is an important tool that can be integrated with other information (e.g., survey studies of organism populations, life cycle and behavior characteristics, sediment geochemistry, and food sources) to assess risks to aquatic organisms in metal‐enriched ecosystems. Environ Toxicol Chem 2024;43:62–73. Published 2023. This article is a U.S. Government work and is in the public domain in the USA. [ABSTRACT FROM AUTHOR]

Traditional methods for estimating abundance of fish populations are not feasible in some systems due to complex population structure and constraints on sampling effort. Lincoln's estimator provides a technique that uses harvest and harvest rate to estimate abundance. Using angler catch data allows assumptions of the estimator to be addressed without relying on methods that could be prohibitively field-intensive or costly. Historic estimates of White Sturgeon Acipenser transmontanus abundance in the Sacramento–San Joaquin River basin have been obtained using mark–recapture methods; however, White Sturgeon population characteristics often cause violations of model assumptions, such as population closure and independent capture probabilities. We developed a version of Lincoln's estimator using a joint likelihood, estimated abundance of White Sturgeon in the Sacramento–San Joaquin River basin in 2015 using this method and empirical data and assessed accuracy and precision of estimates in a simulation study. Estimating abundance using harvest and harvest rate, as represented by our model framework, has the potential to be precise and accurate. The joint likelihood–based approach fitted using Bayesian methods is advantageous because it includes all sources of variation in a single model. Precision of abundance estimates was low with application of the model to White Sturgeon in the Sacramento–San Joaquin River basin and to similar conditions in a simulated dataset. Using simulation, precision and accuracy increased with increases in the number of high-reward and standard tags released, tag reporting rate, tag retention rate, and harvest rate. Results demonstrate potential sources of error when using this approach and suggest that increasing the number of tagged fish and tag reporting rate are potential actions to improve precision and accuracy of abundance estimates of the model. [ABSTRACT FROM AUTHOR]

Predation of fish released as part of conservation aquaculture programs may undermine conservation goals. Identification of factors influencing predation, therefore, can inform management decisions that minimize predation losses. For the endangered Nechako white sturgeon (Acipenser transmontanus Richardson, 1836), the survival of individuals released as part of a conservation aquaculture program is threatened by river otter (Lontra canadensis (Schreber, 1777)) predation. Through the recovery of sturgeon passive integrated transponder (PIT) tags from otter latrines, we set out to quantify the extent of predation, identify spatial patterns in predation including identifying predation hotspots, and understand the timing of predation. The recovery of 3.9% of PIT tags from the hatchery-released sturgeon represents a minimum predation estimate based on several identified factors. The distribution of predation hotspots varied by release cohort, with some consistent hotspots among cohorts. An apparent decrease in predation in recent years was seen in conjunction with fewer live captures and lower release numbers, suggesting some level of density-dependent predation. Results from this study can be used to contribute to management decisions related to Nechako white sturgeon recovery efforts, inform further research needs, and contribute to a growing knowledge of sturgeon predation. [ABSTRACT FROM AUTHOR]

Improving the status of endangered species can be challenging because the efficacy of conservation actions is often uncertain. Conservation aquaculture has been the main recovery action for endangered white sturgeon (Acipenser transmontanus) in the Transboundary Reach of the upper Columbia River. Using long-term mark-recapture data (2002–2018), we predicted variation in growth rates due to genetic, environmental, and competition effects to evaluate the efficacy of the aquaculture program. Environmental conditions (by season and country) and competition had the greatest effects on growth. Growth, length-at-age, weight-at-age, and condition factor were higher for fish residing in reservoir habitats (US) compared to those in riverine habitat (Canada). Growth declined over the study period but growth in length for larger fish remained higher in the US as fish > 100 cm fork length in Canada were not growing. Small differences in growth among families indicate that differences in genetics among parents spawned in the hatchery had negligible effects on growth in the wild. Our estimate of substantive negative density-dependent growth in Canada is important for management of conservation aquaculture for sturgeons. [ABSTRACT FROM AUTHOR]

Abstract Background A new technology for a self-powered acoustic tag (SPT) was developed for active tracking of juvenile fish, intended to avoid the typical battery life constraints associated with active telemetry technology. We performed a laboratory study to evaluate a subdermal tagging technique for the SPT and effects of the tag on survival, tag retention, and growth in juvenile white sturgeon (Acipenser transmontanus). Results Survival was associated with tag retention. White sturgeon implanted with the SPT (n = 30) had 93% survival and tag retention by day 28, 67% by day 101, and 38% by day 595 post-tagging. Sturgeon implanted with a passive integrated transponder (PIT) tag only (control group) had 96% survival and tag retention by day 28, and through day 101 post-tagging. Fish in the PIT group were repurposed after day 101, so no comparisons with this group were made at day 595 post-tagging. Specific growth rate (SGR) for fork length was a median of 0.25% day−1 by day 28 for the SPT group, which was significantly lower than the PIT group (median: 0.42% day−1; n = 27). The SPT and PIT groups had similar SGR fork length by day 101 post-tagging (0.22 and 0.25% day−1, respectively). SGR weight was also lower for the SPT group compared to the PIT group on day 28 (1.39 and 2.11% day−1, respectively), but the difference again dissipated by day 101 (0.79 and 0.88% day−1, respectively). Conclusion The tagging technique and placement of the SPT allowed the tag to remain upright along the flank of the sturgeon to ensure maximum battery output of the SPT; however, retention rates of the SPT were not ideal. We provided suggestions to improve the tagging technique. Suggestions included tagging fish that are > 400 mm FL, moving the incision location to extend the cavity and create a pocket for the placement of the SPT, and performing a quantitative wound-healing evaluation. Future studies are therefore recommended to evaluate these suggestions.

Management objectives for long-lived species are difficult to define because many taxa have delayed maturity and variable recruitment. White Sturgeon Acipenser transmontanus is an example of a species with a complex life history that complicates long-term status monitoring and establishment of management objectives. Historically, White Sturgeon in the Sacramento–San Joaquin River basin have been monitored by tracking the abundance of age-15 individuals as outlined by the Central Valley Project Improvement Act. However, infrequent recruitment complicates progress toward Central Valley Project Improvement Act management objectives because abundance of a single cohort fails to represent overall population trends. By using a Leslie population matrix, we demonstrate that the probability of reaching the Central Valley Project Improvement Act objective of 11,000 age-15 White Sturgeon is highly unlikely. We propose an alternative metric of 155,000 adults, which better represents overall population trends of White Sturgeon in the Sacramento–San Joaquin River basin, can be efficiently monitored, and can support both the goal of the Central Valley Project Improvement Act and management objectives. [ABSTRACT FROM AUTHOR]

Flavobacterium columnare represent one of the most important bacterial pathogens of cultured sturgeon. However, at present there are no commercially available vaccines to prevent infection and treatment options are limited. β-glucans have been shown to be potent immunostimulants that can provide fish protection against infectious disease. In this study, the effects of dietary β-glucan supplementation on disease susceptibility were examined by exposing 0.3% β-glucan-fed white sturgeon (Acipenser transmontanus) to Flavobacterium columnare in laboratory-controlled challenges. Morbidity and mortality were monitored for 15 days post-challenge (dpc). Additionally, transcript levels for pro-inflammatory cytokines, regulatory cytokines and acute phase proteins (APP) were investigated in the spleen and gills at different time points post-challenge. No evidence of protection was observed in β-glucan-fed fish challenged with the bacteria. Moreover, significantly greater mortalities were observed in β-glucan-fed fish challenged with F. columnare (p

The internal organs of white sturgeon in Miyazaki Prefecture are discarded during processing. Therefore, we tried to produce fish sauce using a short-term manufacturing method. The minced internal organs were autolyzed by endogenous proteases at 50 °C. During autolysis, the protein contents of the supernatant and precipitate after centrifugation were analyzed by the Kjeldahl method, and the protein size was monitored by SDS-PAGE. This analysis showed that the extraction rate was about 60% after treatment at 50 °C for 24 h. The major bands at 200 kDa, 43 kDa, and 40 kDa detected before the start of the treatment gradually disappeared over time. Fifteen components were detected as the main volatile components. These components increased sharply and then decreased during incubation at 50 °C for 24 h. The fish sauce produced had a good aroma after incubation at 50 °C for 72 h. [ABSTRACT FROM AUTHOR]

Abundances of important and imperiled fishes of the Snake River Basin continue to decline. We assessed the rationale for breaching the four lower Snake River Basin dams to prevent complete loss of these fishes, and to maximize their likelihood of recovery. We summarize the science surrounding Sockeye Salmon (Oncorhynchus nerka), Chinook Salmon (O. tshawytscha), steelhead (O. mykiss), Bull Trout (Salvelinus confluentus), White Sturgeon (Acipenser transmontanus), and Pacific Lamprey (Entosphenus tridentatus). From this, we drew ten conclusions: (1) development of the Columbia River System (including the Snake River Basin) has converted mainstem rivers into reservoirs, altering fish behavior and survival; (2) most populations currently record their lowest abundance; (3) the Columbia River System dams reduce productivity of diadromous fishes in the highest-quality spawning grounds that could buffer against future climate dynamics; (4) past actions have done little to reduce impacts or precipitate recovery; (5) the Columbia River System constrains survival and productivity of salmon, steelhead and Bull Trout; (6) Snake River Basin salmon and steelhead remain at high extinction risk; (7) eliminating migration impediments and improving mainstem habitats are essential for maintaining genetic diversity and improving Bull Trout persistence; (8) the lower Snake River Basin dams preclude passage of adult White Sturgeon, constraining gene flow and recruitment; (9) the lower Snake River Basin dams impede dramatically passage of adult and juvenile Pacific Lamprey, and (10) Snake River Basin Pacific Lamprey is at high risk of extirpation. Breaching the four lower Snake River Basin dams is an action likely to prevent extirpation and extinction of these fishes. Lessons from the Columbia River System can inform conservation in other impounded rivers.

Understanding life-history diversity in a population is imperative to developing effective fisheries management and conservation practices, particularly in degraded environments with high environmental variability. Here, we examined variation in habitat use and migration patterns of White Sturgeon (Acipenser transmontanus), a long-lived migratory fish that is native to the San Francisco Estuary, CA, United States. Annual increment profiles were combined with respective geochemical (87Sr/86Sr) profiles in sturgeon fin rays to reconstruct annual salinity chronologies for 112 individuals from 5 to 30 years old. Results indicated a complex and diverse amphidromous life history across individuals, characterized largely by estuarine residence, a general ontogenetic trend toward higher-salinity brackish habitats, and high variability in habitat use across all age groups. Hierarchical clustering based on fin ray geochemistry during the first 10 years of life, prior to sexual maturation, indicated at least four distinct migratory phenotypes which differed largely in the timing and duration of juvenile to subadult movements between fresh- and brackish-water habitats. This study provides information regarding habitat use and migration in sub-adult fish that was previously lacking. Different migratory phenotypes vary in exposure to stressors across time and space and populations. Understanding White Sturgeon habitat distributions through space and time at different life stages can help identify areas where habitat restoration would be most effective and develop management actions to reduce stressors associated with specific areas where White Sturgeon are present.

White Sturgeon Acipenser transmontanus are cultured for human consumption as well as for conservation purposes. In this study, two commercially available portable devices for measuring glucose and lactate were compared to a benchtop analyzer and blood reference intervals were generated using heparin plasma collected from 43 healthy White Sturgeon yearlings. The generated normal ranges were used to compare plasma values collected from Veronaea botryosa‐infected White Sturgeon at 10, 20, and 30 d postchallenge (dpc). In the 43 healthy yearlings, significantly different glucose and lactate values were obtained when comparing the portable devices to the benchtop analyzer. In the portable devices, blood glucose showed a consistent bias of 12.3 mg/dL and blood lactate showed a proportional bias. The detected blood glucose values in infected sturgeon were significantly different from those in noninfected controls when using the benchtop analyzer at 20 and 30 dpc and when using the portable device at 20 dpc. However, blood glucose in infected individuals and controls was within the reference interval on either device. No significant difference was noted for lactate measurements in infected sturgeon. The results of this study indicate that portable devices for blood glucose and blood lactate evaluation in White Sturgeon may be useful in a setting where relative values are an acceptable approximation of absolute values. [ABSTRACT FROM AUTHOR]

Background: A new technology for a self-powered acoustic tag (SPT) was developed for active tracking of juvenile fish, intended to avoid the typical battery life constraints associated with active telemetry technology. We performed a laboratory study to evaluate a subdermal tagging technique for the SPT and effects of the tag on survival, tag retention, and growth in juvenile white sturgeon (Acipenser transmontanus). Results: Survival was associated with tag retention. White sturgeon implanted with the SPT (n = 30) had 93% survival and tag retention by day 28, 67% by day 101, and 38% by day 595 post-tagging. Sturgeon implanted with a passive integrated transponder (PIT) tag only (control group) had 96% survival and tag retention by day 28, and through day 101 post-tagging. Fish in the PIT group were repurposed after day 101, so no comparisons with this group were made at day 595 post-tagging. Specific growth rate (SGR) for fork length was a median of 0.25% day−1 by day 28 for the SPT group, which was significantly lower than the PIT group (median: 0.42% day−1; n = 27). The SPT and PIT groups had similar SGR fork length by day 101 post-tagging (0.22 and 0.25% day−1, respectively). SGR weight was also lower for the SPT group compared to the PIT group on day 28 (1.39 and 2.11% day−1, respectively), but the difference again dissipated by day 101 (0.79 and 0.88% day−1, respectively). Conclusion: The tagging technique and placement of the SPT allowed the tag to remain upright along the flank of the sturgeon to ensure maximum battery output of the SPT; however, retention rates of the SPT were not ideal. We provided suggestions to improve the tagging technique. Suggestions included tagging fish that are > 400 mm FL, moving the incision location to extend the cavity and create a pocket for the placement of the SPT, and performing a quantitative wound-healing evaluation. Future studies are therefore recommended to evaluate these suggestions. [ABSTRACT FROM AUTHOR]

The migration of larval fish from spawning to rearing habitat in rivers is not well understood. This paper describes a methodology to predict larval drift using a Lagrangian particle-tracking (LPT) model with passive and active behavioural components loosely coupled to a quasi-three-dimensional hydraulic model. In the absence of measured larval drift, a heuristic approach is presented for the larval drift of two species of interest, white sturgeon (Acipenser transmontanus) and burbot (Lota lota), in the Kootenai River, Idaho. Previous studies found that many fish species prefer certain vertical zones within the water column; sturgeon tend to be found near the bottom and burbot close to the water surface. Limiting the vertical movement of larvae is incorporated into the active component of the LPT model. The results illustrate a pattern of drift where secondary flow in meander bends and other zones of flow curvature redistributes particles toward the outside of the bend for surface drifters and toward the inside of the bend for bottom drifters. This pattern periodically reinforces the intersection of drifting larvae with channel margins in meander bends. In the absence of measured larval drift data, the model provides a tool for hypothesis testing and a guide to both field and laboratory experiments to further define the role of active behaviour in drifting larvae. [ABSTRACT FROM AUTHOR]

The internal organs of white sturgeon in Miyazaki Prefecture are discarded during processing. Therefore, we tried to produce fish sauce using a short-term manufacturing method. The minced internal organs were autolyzed by endogenous proteases at 50 °C. During autolysis, the protein contents of the supernatant and precipitate after centrifugation were analyzed by the Kjeldahl method, and the protein size was monitored by SDS-PAGE. This analysis showed that the extraction rate was about 60% after treatment at 50 °C for 24 h. The major bands at 200 kDa, 43 kDa, and 40 kDa detected before the start of the treatment gradually disappeared over time. Fifteen components were detected as the main volatile components. These components increased sharply and then decreased during incubation at 50 °C for 24 h. The fish sauce produced had a good aroma after incubation at 50 °C for 72 h.

Keywords: otter; PIT tag; predation; radio tag; white sturgeon EN otter PIT tag predation radio tag white sturgeon 780 784 5 12/21/20 20201201 NES 201201 INTRODUCTION White sturgeon ( I Acipenser transmontanus i ) in the Nechako River, British Columbia, Canada have experienced recruitment failure since 1967 (McAdam et al., 2005) and this population was listed as endangered under the Species at Risk Act (SARA) in 2006 (Fisheries & Oceans Canada, 2014). Sturgeon radio tags were collected in suspected otter feeding sites and sturgeon PIT tags were collected from otter latrine sites. It is difficult to be confident that all radio-tagged sturgeon mortalities are a result of river otter predation, however there is evidence that at least a proportion of radio-tag mortalities were caused by otters. [Extracted from the article]

White Sturgeon (Acipenser transmontanus), a species of concern in the San Francisco Estuary, is in relatively low abundance because of a variety of factors. The purpose of our study was to identify the estuarine habitat used by White Sturgeon to aid in the conservation and management of the species locally and across its range. We seasonally sampled subadult and adult White Sturgeon in the central estuary using setlines across a habitat gradient representative of three primary structural elements: shallow wetland channel (mean sample depth = 2 m), shallow open-water shoal (mean sample depth = 2 m), and deep open-water channel (mean sample depth = 7 m). We found that the shallow open-water shoal and deep open-water channel habitats were consistently occupied by White Sturgeon in spring, summer, and fall across highly variable water quality conditions, whereas the shallow wetland channel habitat was essentially unoccupied. We conclude that subadult and adult White Sturgeon inhabit estuaries in at least spring, summer, and fall and that small, shallow wetland channels are relatively unoccupied. [ABSTRACT FROM AUTHOR]

Streptococcus iniae is a zoonotic pathogen and one of the major aetiologic agents of streptococcosis. In White Sturgeon Acipenser transmontanus, S. iniae infection typically presents as a necrotizing and heterophilic myositis, causing 30–50% mortality in infected fish. To gain a better understanding of the pathogenesis of streptococcosis in White Sturgeon, and to identify the experimental route of infection that most closely mimics the natural disease, fingerlings were challenged with a single dose of 1.3 × 108 cells/fish of S. iniae that was administered via intracoelomic/intraperitoneal (IC) or intramuscular (IM) routes. Acute mortalities were present only in the IM‐challenged fish, with first mortality occurring 4 d postchallenge and the mortality rate reaching 18.3% after 9 d. The challenged fish presented erratic swimming, ulcerative skin lesions, and hemorrhages in the liver and swim bladder. Streptococcus iniae was recovered from the kidney and brain tissues of moribund and dead fish. Histopathologic analysis of fish that died acutely revealed massive proliferation of bacteria in the muscle at the injection site and within vascular organs such as the heart and spleen, with variable amounts of tissue necrosis including a necrotizing myositis. Fish that died closer to 9 d postchallenge demonstrated more pronounced multifocal to locally extensive granulomatous inflammation of skeletal muscle at the injection site, liver, kidney, and spleen. No mortality, clinical signs, or gross changes were observed in the control or IC‐challenged fish. Postmortem evaluation of 10 survivors in each treatment was performed to determine carrier status in the brain and posterior kidney tissues. The prevalence of S. iniae in survivors was 10% and 0% in the IM‐ and IC‐challenged groups, respectively. The results from this study suggest that IM‐injection challenge methods are suitable for inducing streptococcosis in White Sturgeon, and they may be the preferred method for studying the pathogenesis of the naturally occurring disease in this species. [ABSTRACT FROM AUTHOR]

Temperature differentially influences developmental trajectories of traits during early life stages that can affect survival and recruitment. Experiments were conducted to quantify temperature-induced developmental responses of White Sturgeon (Acipenser transmontanus) yolk-sac larvae (YSL) reared at temperatures encountered across the species' range (12.5, 14.0, 15.5, and 17.0 °C). We quantified effects of temperature on timing of transitions between sequential developmental stages from hatch to initiation of exogenous feeding. Rate of development significantly increased at warmer compared to cooler temperatures; no significant difference was observed between 15.5 and 17.0 °C or 12.5 and 14.0 °C. When standardized by relative timing of development (RTi), developmental rate was not significantly different among treatments. Morphological traits (total length; body area; yolk-sac area; head area; gill filament area; mouth area; pectoral fin area) were measured daily, though only data for YSL reared at 12.5 and 17.0 °C was used to quantify phenotypic variation. Morphological traits (excluding yolk-sac area) were generally larger 48+ hours post hatch for YSL reared at 17. 0 °C compared to 12.5 °C. In contrast, these same traits, with the exception of gill filament area, were larger in 12.5 °C reared YSL when considered as a function of developmental stage. These opposing results suggest trade-offs associated with allocating resources to a particular trait depended on rearing temperature. Our results provide the ability to estimate timing of critical early life stages (i.e., hatch, emergence) as a function of temperature which is an important management tool to understand how early life development contributes to recruitment processes and adaptability in thermally altered systems. [ABSTRACT FROM AUTHOR]

Outbreaks of an infectious disease affecting cultured white sturgeon (Acipenser transmontanus) were investigated. Clinical signs included erratic swimming, arching of the back and mortality. Necropsy findings included poorly demarcated yellow to dark‐red and friable lesions in the epaxial muscle, ulcerative skin lesions and haemorrhages in the swim bladder and coelomic wall. Histological evaluation revealed areas of necrotizing and heterophilic myositis with aggregates of bacterial cocci. The lumen of blood vessels in the dermis, under ulcerated areas, and in the posterior kidney, was occluded by fibrin thrombi. Aggregates of Gram‐positive cocci were observed in the muscle lesions and within the fibrin thrombi in the dermis and kidney. Genetically homogeneous Streptococcus iniae strains were recovered from affected fish from different outbreaks. The isolates shared high degree of similarity at gene locus (gyrB) with previously characterized S. iniae from cultured fish in California, confirming the emergence of this particular strain of S. iniae in US aquaculture. [ABSTRACT FROM AUTHOR]

This document discusses the challenges faced by White Sturgeon in California, including droughts, habitat loss, and warming water conditions. The California Department of Fish and Wildlife conducted a rescue and monitoring effort to relocate sturgeon from the Tuolumne River to the San Joaquin River to protect their health and reduce the risk of poaching. Acoustic monitoring was used to track the sturgeon's movements after relocation. The document also provides information on a separate monitoring effort in the San Joaquin River and its tributaries, where three sturgeon were tagged and monitored to understand their habitat use and migration patterns. The document acknowledges the individuals and organizations involved in the monitoring effort and provides additional references for further research. [Extracted from the article]

Highlights • Effects of catch-and-release (C&R) angling on wild white sturgeon stress physiology and immediate post-release behaviour are unknown. • Results support the general C&R literature with concentrations of lactate increasing and plasma potassium decreasing with fight time duration. • Tri-axial acoustic accelerometer transmitters were calibrated to identify relative activity for white sturgeon. • Wild accelerometer-tagged white sturgeon were located <75 m from release site and readings showed a decrease in activity 10 min after release. • All 7 accelerometer-tagged sturgeon were located closer to shore after release – suggesting a possible refuge-seeking recovery behaviour. Abstract White sturgeon (Acipenser transmontanus) are anadromous and the largest fish occurring in fresh-water habitats in North America. The largest population is found in the lower Fraser River (LFR), British Columbia, Canada where anglers target the species in a catch-and-release (C&R) recreational fishery. Yet, little is known about the consequences of C&R on these wild fish. Sixty-three angled sturgeon had blood samples taken to assess the physiological stress response relative to fight times. Seven sturgeon were also fitted with acoustic transmitters equipped with accelerometer sensors to assess immediate post-release locomotor behaviour. To understand the relationship between accelerometry and fish behaviour, we calibrated the tags in a lab before deploying them in the field. A physiological stress response was apparent (i.e., increased whole-blood lactate and reduced plasma potassium) and was influenced by fight time. Post-release activity profiles showed a general decrease in activity over time. Post-release displacement was 2–75 m from the release site and all 7 sturgeon were relocated closer to shore. The possible preference we identified for nearshore areas after release should be examined in greater detail in the future as this may lend insight into optimal release locations for white sturgeon. Although C&R mortality rates are low for this species, there is some evidence of transient sub-lethal effects emphasizing the need to refine C&R practices to further improve fish welfare. [ABSTRACT FROM AUTHOR]

Predation and reduced energetic intake have been highlighted as potential mechanisms of recruitment failure in sturgeon populations. These two factors may interact, as foraging carries with it costs of increased predation risk, requiring behavioral trade-offs. We expect that juvenile sturgeon should express predator avoidance behaviors while they are within vulnerable size ranges, yet these behaviors should be modified by nutritional state. To evaluate behavioral trade-offs of juvenile white sturgeon, we designed an experiment to test the interacting effects of acute nutritional state and predation risk on the spatial distribution and movement of small groups (n = 6). Groups were assigned to one of four treatments, designed as a full factorial of nutritional state (well-fed or starved 24-h) and predation risk (largemouth bass present or absent), and eight replicates were conducted for each treatment. Juvenile sturgeon displayed a predicted and adaptive response to predation risk and predator aggression levels by reducing activity levels and displaying marked freezing behavior. Sturgeon responded strongly to nutritional deprivation through increased activity and increased near-neighbor distance, which was likely an adaptive response to increase encounter rates with benthic food items. Both of these responses to starvation were suppressed in the presence of predators. This study has provided experimental evidence that predators can abruptly reduce the foraging activity of white sturgeon, possibly reducing growth rates and extending the period of juvenile vulnerability. Future conservation planning should consider the interacting effects of multiple stressors experienced by sturgeon at early life-stages, as introduced predators and degraded foraging habitats may have interacting effects. [ABSTRACT FROM AUTHOR]

Veronaea botryosa is the etiological agent of a systemic phaeohyphomycosis known as "fluid belly" in white sturgeon (Acipenser transmontanus). Fluid belly is a critical disease affecting sturgeon aquaculture and the caviar industry for which there are no commercially available vaccines or approved antifungal treatments to manage outbreaks. The primary aim of this study was to investigate the effect of a V. botryosa [conidia], a V. botryosa [mold], and a Saccharomyces cerevisiae [yeast] formalin-killed vaccine on sturgeon immune responses to fungal challenge. Immunization consisted of an initial intracoelomic injection with one of the three treatment preparations, followed by a vaccine booster four weeks later by the same route and dose. Experimental challenge by intramuscular injection with a virulent V. botryosa conidia suspension followed after another four weeks. Non-challenged control fish received injections of PBS. The inactivated vaccines proved safe for white sturgeon fingerlings. Sturgeon immunized with either V. botryosa [mold] or S. cerevisiae [yeast] exhibited a significantly different pro-inflammatory response upon challenge with V. botryosa compared to non-immunized fish. Challenged fish developed clinical signs similar to those reported during natural outbreaks of fluid belly. Positive control treatments (those not immunized but challenged with V. botryosa) experienced the highest mortality; however, survival curves were similar amongst all treatments (p < 0.05). Furthermore, the S. cerevisiae [yeast] vaccine resulted in comparatively lower fungal persistence and fewer lesions following histological analysis. Further efforts evaluating the potential of Saccharomyces spp. as a vaccine candidate against fluid belly are warranted. • Inactivated vaccines against V. botryosa were safe for white sturgeon fingerlings. • Mold and yeast vaccines induced a significant inflammatory response upon challenge. • S. cerevisiae has potential as a vaccine candidate against fluid belly. [ABSTRACT FROM AUTHOR]

An 8-week feeding trial was conducted to investigate the responses of juvenile white sturgeon (Acipenser transmontanus) to elevated dietary selenium (Se) based on the determination of the RNA/DNA ratio in muscle, heat shock protein 70 (Hsp70), and caspase-3/7 in muscle and/or liver tissues. Four semi-purified test diets were prepared by adding different levels of L-selenomethionine (0, 50, 100, and 200 mg/kg diet). The analytical determinations of total Se were 2.2, 19.7, 40.1, and 77.7 mg/kg diet. The sturgeon (initial body weight: 30 ± 2 g; mean ± SEM) were raised in indoor tanks provided with flow through freshwater (18–19 °C). There were three replicates for each dietary treatment with 25 fish per replicate. The liver and muscle tissues were collected at 4 and 8 weeks after feeding the test diets. A significant interaction between duration and levels of dietary Se exposures on RNA/DNA ratio in the muscle tissue was detected (P

Abstract Previous studies have demonstrated reduced performance in triploid fish when reared under suboptimal conditions, which may be the result of a higher susceptibility to stressors when compared to diploids. The goal of this project was to investigate differences in the capacity of diploid (8 N) and triploid (12 N) white sturgeon, Acipenser transmontanus , to respond to both warm acclimation (6-weeks of acclimation to either 18 or 22 °C) and a subsequent acute stress (10-min low water stress). Following the 6-week acclimation, fish were sampled either before or following an acute low water stress. Bioindices of the primary and secondary stress response, hematology and cellular metabolic status were measured. We also sought to determine if time to peak cortisol levels were similar between diploid and triploid sturgeon after exposure to a severe acute stressor (netting stress). While both ploidies had similar primary and secondary responses to acute stress, both with and without warm acclimation, warm acclimation impacted the ability of diploid and triploid white sturgeon to mount a typical stress response to an acute stressor. In response to warm acclimation, triploids exhibited little change in branchial lactate dehydrogenase activity, while diploids increased activity. After exposure to an acute water reduction stress, diploids increased citrate synthase activity, yet triploids showed a decrease in activity. Differences in metabolic enzyme activity in response to warm acclimation and acute stress suggest triploid white sturgeon may have a reduced cellular metabolic capacity under chronic and acute stress, which may impact performance of triploid sturgeon in suboptimal conditions. [ABSTRACT FROM AUTHOR]

Limited food availability and altered thermal regimes (e.g. cold water releases from dams) are two common stressors threatening the persistence of fishes inhabiting anthropogenically disturbed freshwater systems. Yet, the combined effects of these stressors remain poorly characterised.To remedy this, we examined the isolated and combined effects of low temperature exposure and food restriction on specific growth rate (SGR, % body mass/day) and upper thermal tolerance (critical thermal maxima, CTMax) in larval white sturgeon (Acipenser transmontanus [Acipenseridae], 32 days post‐hatch, body mass: 0.25 ± 0.03 g, mean ± standard deviation). A 2 × 2 factorial design was implemented with fish exposed to one of two ecologically‐relevant acclimation temperatures (cold exposure: 11°C or a control temperature: 18°C) and one of two food restriction treatments designed to emulate observed declines in food availability (100% or 40% optimal feed rate) for 6 weeks (N: 3 replicate tanks/treatment, 50 fish/tank).Specific growth rate was affected by both low temperature exposure and food restriction in isolation; low temperature exposure reduced SGR by 56.5% and food restriction reduced SGR by 30.6%. Simultaneous exposure to low temperature and food restriction resulted in a greater but less than additive reduction in SGR (80.6%), indicating that the stressors interacted antagonistically.Critical thermal maxima were c. 2°C higher in 18°C‐acclimated fish (CTMax = 30.7 ± 0.4°C, mean ± standard error) compared to 11°C‐acclimated fish (CTMax = 28.6 ± 0.2°C, mean ± standard error); however, CTMax was independent of food restriction in both 11°C‐ and 18°C‐acclimated fish.These data highlight the unpredictability of stressor interactions and may guide holistic conservation strategies, which target co‐occurring stressors in freshwater habitats. [ABSTRACT FROM AUTHOR]

Early–life stage white sturgeon are sensitive to copper (Cu), with adverse behavioral responses observed during previous studies. The objectives of the present study were to quantify the effects of Cu exposure on white sturgeon swimming and feeding behaviors and determine their time to response. Larval sturgeon (1–2, 28, or 35 d posthatch [dph]) were exposed to Cu (0.5–8 μg/L) for 4 to 14 d. Abnormal behavioral changes were observed within the first few days of exposure including loss of equilibrium and immobilization. Digital video tracking software revealed decreased swimming activity with increasing Cu concentration. Significant changes in behavior and mortality occurred at concentrations of Cu between 1 and 8 μg/L. Juvenile white sturgeon, 58 dph, exposed to 12 μg/L Cu consumed 37 to 60% less food than controls after 3 d of exposure. The present results indicate that behavioral endpoints were more sensitive than some standard toxicity test endpoints and can effectively expand the sensitivity of standard toxicity tests for white sturgeon. Swimming behavior was impaired to the extent that survival in the field would likely be jeopardized. Such data would provide managers a useful metric for characterizing the risks of Cu contamination to white sturgeon. Environ Toxicol Chem 2019;38:132–144. Published 2018 Wiley Periodicals Inc. on behalf of SETAC. This article is a US government work and, as such, is in the public domain in the United States of America. [ABSTRACT FROM AUTHOR]

Previous studies suggest fish with additional copies of their genome (polyploids) underperform in suboptimal conditions and may be more susceptible to stress and disease. The objective of this study was to determine the role ploidy plays in the physiological response of white sturgeon to chronically elevated water temperatures. White sturgeon of two ploidies (8 N and 10 N) were acclimated to ambient (18 °C) and warm (22 °C) water. Bioindices of stress (plasma cortisol, glucose and lactate, total erythrocyte count, hematocrit, hemoglobin, mean erythrocyte volume, mean erythrocyte hemoglobin, and mean erythrocyte hemoglobin concentration), immunity (respiratory burst, plasma lysozyme, and total leukocyte count), and cellular metabolic capacity (lactate dehydrogenase and citrate synthase activity) were measured before and after a 6-week acclimation period. Both ploidies appear comparable in their constitutive immune and stress parameters and respond similarly to warming. Hematological indices suggest 8 N and 10 N sturgeon are similar in oxygen carrying capacity; however, differences in enzyme activity between ploidies indicate that 10 N sturgeon may have a lower cellular aerobic capacity. Our results have implications for the screening and management of ploidy on white sturgeon farms and hatcheries, as the differences between ploidies may affect 10 N sturgeon performance at elevated water temperatures. Further research is needed to elucidate the differences in inducible stress and immune responses and metabolism of white sturgeon of different ploidies. [ABSTRACT FROM AUTHOR]

Abstract: Field reports indicate that many White Sturgeon Acipenser transmontanus ingest hooks internally, but the length of time required for hooks to corrode, facilitating passage through their digestive system, is not well understood. Using a buffered acidic solution to simulate stomach conditions, a laboratory experiment was used to estimate the speed at which sturgeon‐sized hooks (2.0‐mm wire diameter) lost weight and compression strength and to evaluate whether loss of hook weight and compression strength was affected by hook abrasion, such as may occur when baited hooks are bounced along the bottom of the river or when ingested hooks are ground between hard food items in the gizzard of a sturgeon. After 399 d, hooks lost an estimated 34% of their weight and 70% of their compression strength. Abrading the hooks with stones before and throughout the study accelerated weight loss by 34% (after 399 d) compared with nonabraded hooks but did not accelerate the loss of compression strength. Abrasion increased the variability between hooks in weight loss but not in compression strength. Regardless of hook abrasion, the compression strength of some hooks was reduced essentially to 0 N within 1 year of constant exposure to stomach‐like acidic conditions. [ABSTRACT FROM AUTHOR]

Summary: Mark‐recapture (M/R) surveys are a standard approach for monitoring White Sturgeon (WS) Acipenser transmontanus populations; however, they can be resource‐intensive, may affect fish health, and often lack enough precision to detect population change reliably. Hydroacoustics surveys provide a non‐intrusive method that is well‐established in fisheries research, but have been applied relatively seldom to sturgeon populations. During 2016, an alternative method was tested for estimating WS abundance by using side‐scan sonar within a 58‐km reach in the middle Snake River, Idaho, USA, and comparing the results to a standard M/R estimate. Using replicate count data within a N‐Mixture model, the sonar method estimated a lower abundance with higher precision (153, 101–213 95% Bayesian credible interval) than that of M/R (219, 138–398 95% confidence interval). Relative to M/R, side‐scan sonar took 75% fewer sample‐days, exhibited overlapping abundance estimates, and provided similar sturgeon length distributions. These results suggest that side‐scan sonar can provide a rapid and precise alternative to M/R for estimating sturgeon abundance. [ABSTRACT FROM AUTHOR]

Summary: The goals were to (i) determine if river discharge and water temperature during various early life history stages were predictors of age‐0 White Sturgeon, Acipenser transmontanus, recruitment, and (ii) provide an example of how over‐dispersed catch data, including data with many zero observations, can be used to better understand the effects of regulated rivers on the productivity of depressed sturgeon populations. An information theoretic approach was used to develop and select negative binomial and zero‐inflated negative binomial models that model the relation of age‐0 White Sturgeon survey data from three contiguous Columbia River reservoirs to river discharge and water temperature during spawning, egg incubation, larval, and post‐larval phases. Age‐0 White Sturgeon were collected with small mesh gill nets in The Dalles and John Day reservoirs from 1997 to 2014 and a bottom trawl in Bonneville Reservoir from 1989 to 2006. Results suggest that seasonal river discharge was positively correlated with age‐0 recruitment; notably that discharge, 16 June–31 July was positively correlated to age‐0 recruitment in all three reservoirs. The best approximating models for two of the three reservoirs also suggest that seasonal water temperature may be a determinant of age‐0 recruitment. Our research demonstrates how over‐dispersed catch data can be used to better understand the effects of environmental conditions on sturgeon populations caused by the construction and operation of dams. [ABSTRACT FROM AUTHOR]

Summary: The goal of this study was to evaluate four implantation techniques by assessing transmitter retention, survival, growth, and wound healing responses in white sturgeon (Acipenser transmontanus Richardson, 1836). A new acoustic transmitter (AT; cylindrical, 0.7 g in air, 24.2 × 5.0 mm, up to 365 days battery life) was developed to monitor age‐0 sturgeon; however, an implantation technique is critical to provide guidance for its use in field research. Sturgeon (n = 150, 182–289 mm fork length, 35–116 g) were separated into five treatments (n = 30 per treatment): (i) control, (ii) flank incision with one suture, (iii) flank incision without a suture, (iv) offline incision with one suture, and (v) offline incision without a suture. Fish were implanted with a non‐functioning AT and observed for 28 days. Transmitter retention was 100% and only fish in the offline incision without a suture treatment had reduced growth (0.15% mm growth per day) compared to controls (0.38%) over the 28 days study. Suturing caused an increase in incision inflammation, ulceration, and water mold infection. Offline incisions were more susceptible to varicosities than flank incisions. Non‐sutured incisions showed greater incision openness, but only during the first 14 days post‐implantation. A flank incision without a suture is recommended for implanting this new AT in age‐0 white sturgeon. [ABSTRACT FROM AUTHOR]

Summary: Determining the age at which farmed sturgeon begin storing ovarian fat will potentially enable sturgeon farmers to adjust husbandry practices, such as feeding different dietary fat levels at an early age. We investigated the influence of dietary fat on the size of ovarian adipocytes in farmed age‐2 white sturgeon Acipenser transmontanus. At age 1 month, all fish were fed a commercial high fat (HF; 17% fat) diet. At age 6 months, half were transitioned to an experimental low fat (LF; 9% fat) diet. Fish at this time averaged 160 g (±30 g), and individual tank density was 4.1 kg/m3. Tanks were 3.7 m in diameter, 1.3 m deep, each with a volume of 13.7 m3. Each tank maintained a flow rate of 150 L/min using groundwater with water temperatures ranging from 19 to 21°C and dissolved oxygen ranging from 6.5 to 12.0 ppm. All fish were fed the diet assigned to their tank for an additional 18 months prior to sampling. At age 25 months (now referred to as “age 2”), tissue was collected from fish and processed histologically. Adipocytes were measured along the ovarian fold (anterior), furthest from the ovarian fold (posterior), and randomly in between the anterior and posterior sections. Randomly chosen adipocytes from each location were measured histologically. Mean adipocyte size did not statistically differ among sample locations in fish fed the same diet. Once pooled by sampling location, average adipocyte size was 5,491.18 μm (±98.97) in fish fed the HF diet and 3,348.62 μm (±40.85) in fish fed the LF diet. Fish fed the HF diet had larger adipocytes than fish fed the LF diets (t = 20.01, df = 78.54, p < .01). The results demonstrate that diet can influence the size of adipocytes found in juvenile white sturgeon ovaries. Additional research is needed to determine whether the accumulation of large adipocytes as a juvenile confers to adulthood and influences reproductive ability and caviar yield and quality. [ABSTRACT FROM AUTHOR]

Summary: A sanctuary targeting the time and space occupied by reproductively active white sturgeon, Acipenser transmontanus, during spawning can be an effective method for reducing angling‐related stressors. A catch and release (C&R) fishery targeting over the legal limit (oversize; ≥137 cm fork length) white sturgeon had been intensifying since 1990 and grew in popularity through the 2000s in the lower Columbia River. A research project to describe the reproductive structure of the adult white sturgeon population below Bonneville Dam (rkm 220‐233) was initiated in 2000 and provided the first detailed observations of trauma linked to this C&R fishery. Fish captured from 2003 to 2011 were examined for evidence of in‐season angling damage (hook marks, leaders and lines in buccal cavity) from June through August each year. Carcass surveys were conducted weekly from June through August within a 24.8 km stretch downstream from Bonneville Dam. Catch rates were determined through angler interviews and aerial counts of boat and bank anglers. Four major regulation changes occurred during the course of the study affecting the seasonal spawning sanctuary in space and time. A total of 679 oversize white sturgeon were examined for evidence of in‐season angling damage. The proportion of individuals with evidence of angling, damage indicators per individual, number of carcasses found and the number of carcasses with observed evidence of angling or retained gear, and the total number of oversize fish handled by boat anglers declined after each fishing regulation change. The trends suggest that the sanctuary influenced the number of encounters between anglers and white sturgeon and that increases to the sanctuary in time and space reduced stress endured by oversize white sturgeon. [ABSTRACT FROM AUTHOR]

Abstract: The issue of deep hooking is of concern in white sturgeon, Acipenser transmontanus Richardson, fisheries because nearly all anglers use bait with a stationary presentation on the river bottom to catch them, and bait fishing is often associated with higher instances of deep hooking and hooking mortality. Deep hooking rates, landing success and catch rates were investigated for anglers bait fishing for white sturgeon using circle and J hooks with inline and offset alignments fished with both active and passive hook‐setting methods. Anglers hooked 578 white sturgeon and landed 508 fish, ranging in size from 60 to 316 cm total length (mean = 137 cm). Deep hooking rates averaged 0.6% and did not differ between hook types, hook alignments or hook‐setting methods. Landing success (the proportion of hooked sturgeon that were successfully landed) and catch rates were also equivalent between hook types, hook alignments and hook‐setting methods; landing success averaged 88% and catch rates averaged 0.27 fish/hr. Results of this study indicate that deep hooking is rare when angling for white sturgeon using standard bait‐fishing gear regardless of hook‐setting method or whether circle or J hooks were used; regulations restricting hook type in sturgeon bait fisheries are therefore unwarranted. [ABSTRACT FROM AUTHOR]

Many populations of migratory fish species, including white sturgeon (Acipenser transmontanus Richardson), are threatened due to modification of riverine systems and may experience downstream displacement or mortality at water intake structures. Efforts to reduce the impacts of these structures are beginning to incorporate behavioural guidance, where the sensory capabilities of fishes are exploited to repel them from high-risk areas or attract them towards desirable paths. Artificial lighting has been tested before, but consisted of single-spectrum lights. Using a new programmable LED-based light guidance device (LGD), we exposed age-0 white sturgeon to light strobing at 1 Hz, 20 Hz, or constant illumination with colours (green, red, blue) matching the absorbance maxima of their retinal photopigments. The behavioural responses of the sturgeon were assessed using y-maze dichotomous choice tests under both day (light) and night (dark) conditions. Sturgeon demonstrated positive phototaxis under both day and night conditions, and approached the LGD more often when light was continuous or strobing at 20 Hz compared to strobing at 1 Hz. Green light elicited the greatest rates of attraction overall. The combination of strobing and colour may help to protect imperiled fish from waterway development and serve as an effective form of mitigation at hydropower facilities and other human infrastructure where fish may be entrained or impinged. [ABSTRACT FROM AUTHOR]

Water temperature plays a crucial role in the physiology of aquatic species, particularly in their survival and development. Thus, resource programs are commonly used to manage water quality conditions for endemic species. In a river system like the Nechako River system, central British Columbia, a water management program was established in the 1980s to alter water release in the summer months to prevent water temperatures from exceeding a 20 °C threshold downstream during the spawning season of Sockeye salmon (Oncorhynchus nerka). Such a management regime could have consequences for other resident species like the white sturgeon (Acipenser transmontanus). Here, we use a hydrothermal model and white sturgeon life stage-specific experimental thermal tolerance data to evaluate water releases and potential hydrothermal impacts based on the Nechako water management plan (1980–2019). Our analysis focused mainly on the warmest five-month period of the year (May to September), which includes the water release management period (July–August). Our results show that the thermal exposure risk, an index that measures temperature impact on species physiology of Nechako white sturgeon across all early life stages (embryo, yolk-sac larvae, larvae, and juvenile) has increased substantially, especially in the 2010s relative to the management program implementations' first decade (the 1980s). The embryonic life stage was the most impacted, with a continuous increase in potential adverse thermal exposure in all months examined in the study. We also recorded major impacts of increased thermal exposure on the critical habitats necessary for Nechako white sturgeon recovery. Our study highlights the importance of a holistic management program with consideration for all species of the Nechako River system and the merit of possibly reviewing the current management plan, particularly with the current concerns about climate change impacts on the Nechako River. • We use a hydrothermal model and white sturgeon life stage-specific experimental thermal tolerance data. • Evaluated water releases and hydrothermal impacts based on the Nechako water plan and computed the thermal exposure risk. • The risk has increased substantially in the 2010s relative to the water plan implementations' first decade-1980s. • There is a need for a holistic water plan with consideration for all species of the Nechako River system. [ABSTRACT FROM AUTHOR]

Veronaea botryosa is a melanized mold and cause of systemic fungal infections in cultured sturgeon (Acipenser spp.). Mortality in adult female sturgeon caused by this emergent pathogen results in significant economic losses for the caviar industry. Little is known regarding environmental conditions conducive to V. botryosa infection. This study evaluated the effect of temperature on V. botryosa infectivity and dissemination following intramuscular injection challenge of white sturgeon maintained at 13 or 18 °C for 40 days. Daily mortality was recorded and persistence of the fungus in the livers of moribund and surviving fish was investigated using culture and histopathological analysis. Fish maintained at 18 °C developed systemic phaeohyphomycosis and had significantly greater mortality than controls and fish maintained at 13 °C (p < 0.05). Challenged fish, regardless of temperature, exhibited lesions in multiple organs. However, muscle lesions, angioinvasion and systemic dissemination were more severe and widespread in fish challenged at the higher temperature. In vitro cytotoxicity of V. botryosa was evaluated in white sturgeon skin (WSSK-1) and epithelioma papulosum cyprini (EPC) cell lines inoculated at spore:cell ratios of 1:10, 1:1 and 10:1, then incubated 15, 20 and 25 °C. Cytotoxicity, as indicated by quantifying the release of lactate dehydrogenase into culture supernatants, increased with increasing spore dose and incubation temperature in both fish cell lines. Findings suggest that temperature significantly influences the development of systemic V. botryosa infection in white sturgeon and that WSSK-1 and EPC cells are suitable in vitro models for the study of host--pathogen interactions between V. botryosa and fish epithelial cells. [ABSTRACT FROM AUTHOR]