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This study sought to determine whether wild white sturgeon from the Columbia River (Oregon) were exhibiting signs of reproductive endocrine disruption. Fish were sampled in the free-flowing portion of the river (where the population is experiencing reproductive success) and from three reservoirs behind hydroelectric dams (where fish have reduced reproductive success). All of the 18 pesticides and almost all of the 28 polychlorinated biphenyls (PCBs) that were analyzed in livers and gonads were detected in at least some of the tissue samples. Metabolites of p,p -dichlorodiphenyltrichloroethane (DDT) [p,p -dichlorodiphenyldichloroethylene (DDE) and p,p -1,1-dichloro-2,2-bis(4-chlorophenyl)ethane (DDD)]were consistently found at relatively high levels in fish. Some males and immature females showed elevated plasma vitellogenin; however, concentrations were not correlated with any of the pesticides or PCBs analyzed. Negative correlations were found between a number of physiologic parameters and tissue burdens of toxicants. Plasma triglycerides and condition factor were negatively correlated with total DDT (DDD + DDE + DDT), total pesticides (all pesticides detected - total DDT), and PCBs. In males, plasma androgens and gonad size were negatively correlated with total DDT, total pesticides, and PCBs. Fish residing in the reservoir behind the oldest dam had the highest contaminant loads and incidence of gonadal abnormalities, and the lowest triglycerides, condition factor, gonad size, and plasma androgens. These data suggest that endocrine-disrupting chemicals may be accumulating behind dams over time. Overall, results of this study indicate that exposure to environmental contaminants may be affecting both growth and reproductive physiology of sturgeon in some areas of the Columbia River. [ABSTRACT FROM AUTHOR]

Here, we provide evidence that the freshwater parasitic copepod, Salmincola californiensis, acts as a vector for Aeromonas salmonicida. While investigating the effects of S. californiensis on Chinoook salmon (Oncorhynchus tshawytscha), we tangentially observed that fish infected with the copepod developed furunculosis, caused by A. salmonicida. This occurred despite being reared in pathogen-free well water in a research facility with no prior history of spontaneous infection. We further investigated the possibility of S. californiensis to serve as a vector for the bacterium via detection of fluorescently labelled A. salmonicida inside the egg sacs from copepods in which the fish hosts were experimentally infected with GFP-A449 A. salmonicida. We then evaluated copepod egg sacs that were collected from adult Chinook salmon from a freshwater hatchery with A. salmonicida infections confirmed by either culture or PCR. The bacterium was cultured on tryptic soy agar plates from 75% of the egg sacs, and 61% were positive by PCR. These three separate experiments indicate an alternative tactic of transmission in addition to direct transmission of A. salmonicida in captivity. The copepod may play an important role in transmission of the bacterium when fish are more dispersed, such as in the wild., (© 2023 John Wiley & Sons Ltd.)

Prespawn mortality (PSM) presents a major problem for the recovery of spring Chinook Salmon (Oncorhynchus tshawytscha) populations. In the Willamette River, Oregon, PSM exceeds 90% in some years but factors explaining it are not well understood. We examined intestinal tissue samples using histological slides from over 783 spring Chinook Salmon collected between 2009 and 2021, which included tissues from PSM fish, artificially spawned captive broodstock (BS) and normal river run fish, comprised of trapped (Live) and naturally post-spawned river (RPS) fish collected from the river. We observed degeneration of the intestinal epithelium and loss of villous structure, with concurrent severe enteritis. A natural progression of decline in epithelial integrity (EI) through the summer and fall until spawning and subsequent death was also observed. Live fish exhibited high EI scores (mean = 68%), BS exhibited variable EI scores (35%) and RPS exhibited severe loss of EI (14%). PSM fish exhibited prominent loss of intestinal epithelium with EI scores (13%), very similar to RPS fish, despite having been collected earlier in the year. Hence, we argue that low EI scores are strongly linked with PSM. Ceratonova shasta and Enterocytozoon schreckii were common in all groups, but neither were linked to either PSM or a decline in EI., (© 2023 John Wiley & Sons Ltd.)

Pacific salmon experience prolonged elevation in corticosteroid hormones during important life history events including migration, reproduction, and senescence. These periods of elevated corticosteroids correspond with changes to immunity and energy metabolism; therefore, fish may be particularly vulnerable to mortality at these times. Recent studies found that stress-induced cortisol release associated with microbial community shifts in salmonids, raising the question of how longer-term corticosteroid dynamics that accompany life history transitions affect salmonid microbiomes. In this work, we experimentally evaluated the relationships between gut microbiome composition, chronically elevated corticosteroids, and mortality in juvenile Chinook salmon (Oncorhynchus tshawytscha). We found that treatment with slow-release implants of the corticosteroids cortisol or dexamethasone resulted in changes to the gut microbiome. Morbidity was also associated with microbiome composition, suggesting that the gut microbiome reflects individual differences in susceptibility to opportunistic pathogens. Additionally, we analyzed a small number of samples from adult fish at various stages of senescence. Results from these samples suggest that microbiome composition associated with gut integrity, and that the microbial communities of corticosteroid treated juveniles shift in composition toward those of senescent adults. Overall, findings from this work indicate that the gut microbiome correlates with mortality risk during periods of chronic corticosteroid elevation., (© 2023. The Author(s).)

Pacific salmon (Oncorhynchus spp.) rearing in lakes and reservoirs above dams have been known to become heavily infected with an ectoparasitic copepod (Salmincola californiensis). Little is known about the factors that affect the parasite infection prevalence and intensity. However, previous research suggests that the parasite may negatively affect the fitness and survival of the host fish. The effect of water temperature, confinement and the density of the free-swimming infectious stage of S. californiensis, the copepodid, on infection prevalence and intensity was evaluated by experimentally exposing juvenile Chinook Salmon (O. tshawytscha). Infection rates observed in wild populations were achieved under warm water (15-16°C) and high copepodid density (150-300/L) treatment conditions. Infection prevalence and intensity were also significantly higher in larger fish. During the infection experiment, 4.5% of infected fish died within 54 days with mortality significantly related to copepod infection intensity. The potential for autoinfection was compared to cross-infection by cohabitation of infected fish with naïve fish. Previously infected fish had significantly greater infection intensity compared with naïve fish, indicating that infected fish can be reinfected and that they may be more susceptible than naïve fish., (© 2021 John Wiley & Sons Ltd. This article is a U.S. Government work and is in the public domain in the USA.)

Understanding and preserving intraspecific diversity (ISD) is important for species conservation. However, ISD units do not have taxonomic standards and are not universally recognized. The terminology used to describe ISD is varied and often used ambiguously. We compared definitions of terms used to describe ISD with use in recent studies of three fish taxa: sticklebacks (Gasterosteidae), Pacific salmon and trout ( Oncorhynchus spp., "PST"), and lampreys (Petromyzontiformes). Life history describes the phenotypic responses of organisms to environments and includes biological parameters that affect population growth or decline. Life-history pathway(s) are the result of different organismal routes of development that can result in different life histories. These terms can be used to describe recognizable life-history traits. Life history is generally used in organismal- and ecology-based journals. The terms paired species/species pairs have been used to describe two different phenotypes, whereas in some species and situations a continuum of phenotypes may be expressed. Our review revealed overlapping definitions for race and subspecies, and subspecies and ecotypes. Ecotypes are genotypic adaptations to particular environments, and this term is often used in genetic- and evolution-based journals. "Satellite species" is used for situations in which a parasitic lamprey yields two or more derived, nonparasitic lamprey species. Designatable Units, Evolutionary Significant Units (ESUs), and Distinct Population Segments (DPS) are used by some governments to classify ISD of vertebrate species within distinct and evolutionary significant criteria. In situations where the genetic or life-history components of ISD are not well understood, a conservative approach would be to call them phenotypes., Competing Interests: None declared., (© 2021 The Authors. Ecology and Evolution published by John Wiley & Sons Ltd.)

We tested the prediction that a complex physical rearing environment would enhance short-term spatial memory as assessed by learning ability in a spatial navigation task in juvenile Chinook salmon Oncorhynchus tshawytscha. We reared fish in two low-density treatments, where fish were either in bare fiberglass tanks (bare) or in tanks with physical structure (complex). We also tested conventionally reared high-density hatchery fish to compare with these other experimental treatments. Our reason for including this third hatchery treatment is that the two low-density treatments, aside from the manipulation of structure, followed a rearing programme that is designed to produce fish with more wild-like characteristics. We tested individually marked fish for seven consecutive days and recorded movement and time to exit a testing maze. Stimulus conspecific fish outside the exit of the maze provided positive reinforcement for test fish. Fish from the bare treatment were less likely to exit the start box compared with fish in the complex and hatchery treatments. However, fish in the hatchery treatment were significantly more likely to exit the maze on their own compared with both the bare and complex treatments. Hatchery fish effectively learned the task as shown by a decrease in the number of mistakes over time, but the number of mistakes was significantly greater on the first day of trials. Increasing habitat complexity with structure may not necessarily promote spatial learning ability, but differences between hatchery and experimental treatments in rearing density and motivation to be near conspecifics likely led to observed behavioural differences., (© 2019 The Fisheries Society of the British Isles.)

The relative movement of juvenile steelhead Oncorhynchus mykiss reared on two treatments was investigated to provide insight on the effect of structure in the rearing environment on the behaviour of the fish before potential release into a natural river system. The progeny of wild broodstock were reared either in the presence or absence of structure in the tank environment for 7 months at the Oregon Hatchery Research Center located in Oregon, U.S.A. Behavioural assessments, including movement response to a simulated predator, showed that fish reared on structure moved a similar amount (based on line crosses) as fish reared in bare hatchery tanks. No significant difference was observed in the proportion of time spent near a small structure within the behavioural test tank between the two treatments, but all fish showed decreased movement over time with each subsequent predation event. Fish from both treatments spent 30% of their time in the section of the tank containing the structure, which was one section out of a total of eight sections. In both treatments, fish foraged 20% of the time in the 2 min following the introduction of live tubifex prey (two separate events). Overall, similar movement and foraging responses occurred following mock predation events for juveniles reared either with or without structure. Developing assessment tools such as these, that measures behaviours related to survival based on rearing environment should allow managers to better predict the survival and effect of rearing conditions on the release of hatchery-origin fish into the wild., (© 2018 The Fisheries Society of the British Isles.)

When fish perceive stressful scenarios, their hypothalamus-pituitary-interrenal axis is activated resulting in the release of corticotropin releasing hormone, adrenocorticotropic hormone (ACTH), and finally cortisol. The physiologic stress response of fish has most often been linked to the reduced performance of the immune system, with a few exceptions where the immune system is activated. In this report, we tested the hypothesis that oxidative burst activity levels in juvenile Chinook salmon (Oncorhynchus tshawytscha) are altered when the fish is presented with a stressor. Fish were subjected to a stressor for 3 h and then allowed to recover for 20 h following the stressor. Plasma and spleens were collected from euthanized fish before the stressor, at the end of a 3 h stressor, and 23 h after the start of the experiment. Plasma was held at -80 °C until cortisol radioimmunoassay analysis was performed to confirm stress. Spleens were held in Dulbecco's Modified Eagle Medium overnight and analyzed the day following collection. Oxidative burst activity was measured in splenic leukocytes after being stimulated with phorbol 12-myristate 13-acetate. We found a significant increase in activated oxidative burst from fish subjected to the stressor as compared to unstressed fish. Speculation is given to ACTH being the leukocyte priming agent in this experiment rather than the cortisol itself., (Copyright © 2018. Published by Elsevier Ltd.)

The effects of egg size on early development and growth of steelhead Oncorhynchus mykiss were recorded for more than 200 days following hatching. Fish from smaller eggs hatched sooner and at a smaller size than fish from larger eggs, but fish from smaller eggs showed consistently higher growth rates than fish from larger eggs. Since many life-history attributes appear to be determined by size or growth rate at age during the first year, egg size could be a significant predictor of important changes in the life history of individuals., (© 2018 The Fisheries Society of the British Isles.)

Juvenile Chinook Salmon Oncorhynchus tshawytscha moving downstream through tributaries of the upper Willamette River basin can spend months in reservoirs created by dams. While residing in the reservoirs, they often obtain heavy infections of the freshwater parasitic copepod Salmincola californiensis. The physiologic effect these parasites have on salmonids is poorly understood. We developed a method to infect juvenile Chinook Salmon in a laboratory with the copepodid stage of S. californiensis. Infected and uninfected fish were subjected to a swimming challenge to ascertain swimming endurance. Severity of gill damage was assessed using a dissecting microscope. Juvenile Chinook Salmon naturally infected with S. californiensis in Cougar Reservoir, Oregon, were also challenged and compared with their lab-infected counterparts. Copepod infection greatly impaired the swimming ability of laboratory fish, and the naturally infected fish were entirely incapable of swimming at low velocity. Chinook Salmon collected in the wild were more heavily infected than the laboratory fish and had trouble surviving collection and transport to our laboratory. The intensity of infection and severity of gill damage were positively correlated with diminished swimming ability, suggesting that heavy infection with copepods impairs gas exchange and osmotic regulation, which likely results in diminished fitness and decreased survival of infected fish., (© 2017 American Fisheries Society.)

Variation in early life history traits often leads to differentially expressed morphological and behavioral phenotypes. We investigated whether variation in egg size and emergence timing influence subsequent morphology associated with migration timing in juvenile spring Chinook Salmon, Oncorhynchus tshawytscha . Based on evidence for a positive relationship between growth rate and migration timing, we predicted that fish from small eggs and fish that emerged earlier would have similar morphology to fall migrants, while fish from large eggs and individuals that emerged later would be more similar to older spring yearling migrants. We sorted eyed embryos within females into two size categories: small and large. We collected early and late-emerging juveniles from each egg size category. We used landmark-based geometric morphometrics and found that egg size appears to drive morphological differences. Egg size shows evidence for an absolute rather than relative effect on body morphology. Fish from small eggs were morphologically more similar to fall migrants, while fish from large eggs were morphologically more similar to older spring yearling migrants. Previous research has shown that the body morphology of fish that prefer the surface or bottom location in a tank soon after emergence also correlates with the morphological variations between wild fall and spring migrants, respectively. We found that late-emerging fish spent more time near the surface. Our study shows that subtle differences in early life history characteristics may correlate with a diversity of future phenotypes.

This study used existing western brook lamprey Lampetra richardsoni age information to fit three different growth models (i.e. von Bertalanffy, Gompertz and logistic) with and without error in age estimates. Among these growth models, there was greater support for the logistic and Gompertz models than the von Bertalanffy model, regardless of ageing error assumptions. The von Bertalanffy model, however, appeared to fit the data well enough to permit survival estimates; using length-based estimators, annual survival varied between 0·64 (95% credibility interval: 0·44-0·79) and 0·81 (0·79-0·83) depending on ageing and growth process error structure. These estimates are applicable to conservation and management of L. richardsoni and other western lampreys (e.g. Pacific lamprey Entosphenus tridentatus) and can potentially be used in the development of life-cycle models for these species. These results also suggest that estimators derived from von Bertalanffy growth models should be interpreted with caution if there is high uncertainty in age estimates., (© 2016 The Fisheries Society of the British Isles.)

Many anthropogenic disturbances have contributed to the decline of Pacific lampreys (Entosphenus tridentatus), but potential negative effects of contaminants on lampreys are unclear. Lamprey ammocoetes are the only detritivorous fish in the lower Willamette River, Oregon, USA, and have been observed in Portland Harbor sediments. Their long benthic larval stage places them at risk from the effects of contaminated sediment. The authors developed experimental methods to assess the effects of contaminated sediment on the growth and behavior of field-collected ammocoetes reared in a laboratory. Specifically, they developed methods to assess individual growth and burrowing behavior. Burrowing performance demonstrated high variability among contaminated sediments; however, ammocoetes presented with noncontaminated reference sediment initiated burrowing more rapidly and completed it faster. Ammocoete reemergence from contaminated sediments suggests avoidance of some chemical compounds. The authors conducted long-term exposure experiments on individually held ammocoetes using sediment collected from their native Siletz River, which included the following: contaminated sediments collected from 9 sites within Portland Harbor, 2 uncontaminated reference sediments collected upstream, 1 uncontaminated sediment with characteristics similar to Portland Harbor sediments, and clean sand. They determined that a 24-h depuration period was sufficient to evaluate weight changes and observed no mortality or growth effects in fish exposed to any of the contaminated sediments. However, the effect on burrowing behavior appeared to be a sensitive endpoint, with potentially significant implications for predator avoidance. Environ Toxicol Chem 2016;35:2092-2102. © 2016 SETAC., (© 2016 SETAC.)

Studies on hydromineral balance in fishes frequently employ measurements of electrolytes following euthanasia. We tested the effects of fresh- or salt-water euthanasia baths of tricaine mesylate (MS-222) on plasma magnesium (Mg(2+)) and sodium (Na(+)) ions, cortisol and osmolality in fish exposed to saltwater challenges, and the ion and steroid hormone fluctuations over time following euthanasia in juvenile spring Chinook salmon (Oncorhynchus tshawytscha). Salinity of the euthanasia bath affected plasma Mg(2+) and Na(+) concentrations as well as osmolality, with higher concentrations in fish euthanized in saltwater. Time spent in the bath positively affected plasma Mg(2+) and osmolality, negatively affected cortisol, and had no effect on Na(+) concentrations. The difference of temporal trends in plasma Mg(2+) and Na(+) suggests that Mg(2+) may be more sensitive to physiological changes and responds more rapidly than Na(+). When electrolytes and cortisol are measured as endpoints after euthanasia, care needs to be taken relative to time after death and the salinity of the euthanasia bath., (Copyright © 2015 Elsevier Inc. All rights reserved.)

Adult Chinook salmon (Oncorhynchus tshawytscha) migrate from salt water to freshwater streams to spawn. Immune responses in migrating adult salmon are thought to diminish in the run up to spawning, though the exact mechanisms for diminished immune responses remain unknown. Here we examine both adaptive and innate immune responses as well as pathogen burdens in migrating adult Chinook salmon in the Upper Willamette River basin. Messenger RNA transcripts encoding antibody heavy chain molecules slightly diminish as a function of time, but are still present even after fish have successfully spawned. In contrast, the innate anti-bacterial effector proteins present in fish plasma rapidly decrease as spawning approaches. Fish also were examined for the presence and severity of eight different pathogens in different organs. While pathogen burden tended to increase during the migration, no specific pathogen signature was associated with diminished immune responses. Transcript levels of the immunosuppressive cytokines IL-10 and TGF beta were measured and did not change during the migration. These results suggest that loss of immune functions in adult migrating salmon are not due to pathogen infection or cytokine-mediated immune suppression, but is rather part of the life history of Chinook salmon likely induced by diminished energy reserves or hormonal changes which accompany spawning., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

A number of researchers have attempted to estimate salmonid smolt survival during outmigration through an estuary. However, it is currently unclear how the design of such studies influences the accuracy and precision of survival estimates. In this simulation study we consider four patterns of smolt survival probability in the estuary, and test the performance of several different sampling strategies for estimating estuarine survival assuming perfect detection. The four survival probability patterns each incorporate a systematic component (constant, linearly increasing, increasing and then decreasing, and two pulses) and a random component to reflect daily fluctuations in survival probability. Generally, spreading sampling effort (tagging) across the season resulted in more accurate estimates of survival. All sampling designs in this simulation tended to under-estimate the variation in the survival estimates because seasonal and daily variation in survival probability are not incorporated in the estimation procedure. This under-estimation results in poorer performance of estimates from larger samples. Thus, tagging more fish may not result in better estimates of survival if important components of variation are not accounted for. The results of our simulation incorporate survival probabilities and run distribution data from previous studies to help illustrate the tradeoffs among sampling strategies in terms of the number of tags needed and distribution of tagging effort. This information will assist researchers in developing improved monitoring programs and encourage discussion regarding issues that should be addressed prior to implementation of any telemetry-based monitoring plan. We believe implementation of an effective estuary survival monitoring program will strengthen the robustness of life cycle models used in recovery plans by providing missing data on where and how much mortality occurs in the riverine and estuarine portions of smolt migration. These data could result in better informed management decisions and assist in guidance for more effective estuarine restoration projects.

Upriver movements were determined for Chinook salmon Oncorhynchus tshawytscha returning to the Yukon River, a large, virtually pristine river basin. These returns have declined dramatically since the late 1990s, and information is needed to better manage the run and facilitate conservation efforts. A total of 2,860 fish were radio tagged during 2002-2004. Most (97.5%) of the fish tracked upriver to spawning areas displayed continual upriver movements and strong fidelity to the terminal tributaries entered. Movement rates were substantially slower for fish spawning in lower river tributaries (28-40 km d-1) compared to upper basin stocks (52-62 km d-1). Three distinct migratory patterns were observed, including a gradual decline, pronounced decline, and substantial increase in movement rate as the fish moved upriver. Stocks destined for the same region exhibited similar migratory patterns. Individual fish within a stock showed substantial variation, but tended to reflect the regional pattern. Differences between consistently faster and slower fish explained 74% of the within-stock variation, whereas relative shifts in sequential movement rates between "hares" (faster fish becoming slower) and "tortoises" (slow but steady fish) explained 22% of the variation. Pulses of fish moving upriver were not cohesive. Fish tagged over a 4-day period took 16 days to pass a site 872 km upriver. Movement rates were substantially faster and the percentage of atypical movements considerably less than reported in more southerly drainages, but may reflect the pristine conditions within the Yukon River, wild origins of the fish, and discrete run timing of the returns. Movement data can provide numerous insights into the status and management of salmon returns, particularly in large river drainages with widely scattered fisheries where management actions in the lower river potentially impact harvests and escapement farther upstream. However, the substantial variation exhibited among individual fish within a stock can complicate these efforts.

Most pathogen detection tests are imperfect, with a sensitivity < 100%, thereby resulting in the potential for a false negative, where a pathogen is present but not detected. False negatives in a sample inflate the number of non-detections, negatively biasing estimates of pathogen prevalence. Histological examination of tissues as a diagnostic test can be advantageous as multiple pathogens can be examined and providing important information on associated pathological changes to the host. However, it is usually less sensitive than molecular or microbiological tests for specific pathogens. Our study objectives were to 1) develop a hierarchical occupancy model to examine pathogen prevalence in spring Chinook salmon Oncorhynchus tshawytscha and their distribution among host tissues 2) use the model to estimate pathogen-specific test sensitivities and infection rates, and 3) illustrate the effect of using replicate within host sampling on sample sizes required to detect a pathogen. We examined histological sections of replicate tissue samples from spring Chinook salmon O. tshawytscha collected after spawning for common pathogens seen in this population: Apophallus/echinostome metacercariae, Parvicapsula minibicornis, Nanophyetus salmincola/ metacercariae, and Renibacterium salmoninarum. A hierarchical occupancy model was developed to estimate pathogen and tissue-specific test sensitivities and unbiased estimation of host- and organ-level infection rates. Model estimated sensitivities and host- and organ-level infections rates varied among pathogens and model estimated infection rate was higher than prevalence unadjusted for test sensitivity, confirming that prevalence unadjusted for test sensitivity was negatively biased. The modeling approach provided an analytical approach for using hierarchically structured pathogen detection data from lower sensitivity diagnostic tests, such as histology, to obtain unbiased pathogen prevalence estimates with associated uncertainties. Accounting for test sensitivity using within host replicate samples also required fewer individual fish to be sampled. This approach is useful for evaluating pathogen or microbe community dynamics when test sensitivity is <100%.

Ceratomyxa shasta (Myxozoa) is a common gastrointestinal pathogen of salmonid fishes in the Pacific Northwest of the United States. We have been investigating this parasite in adult Chinook salmon ( Oncorhynchus tshawytscha ) in the Willamette River, Oregon. In prior work, we observed differences in the pattern of development of C. shasta in adult salmon compared to juvenile salmon. Adult salmon consistently had large numbers of prespore stages in many of the fish that survived to spawn in the fall. However, myxospores were rarely observed, even though they were exposed and presumably infected for months before spawning. We evaluated the ability of C. shasta to sporulate following fish death because it is reported that myxosores are common in carcasses of Chinook salmon. We collected the intestine from 30 adult salmon immediately after artificial spawning and death (T0). A total of 23 fish were infected with C. shasta based on histology, but only a few myxospores were observed in 1 fish by histology. Intestines of these fish were examined at T0 and T7 (latter held at 17 C for 7 days) using quantified wet mount preparations. An increase in myxospore concentrations was seen in 39% of these fish, ranging between a 1.5- to a 14.5-fold increase. The most heavily infected fish exhibited a 4.6-fold increase from 27,841 to 129,352 myxospores/cm. This indicates, supported by various statistical analyses, that under certain conditions presporogonic forms are viable and continue to sporulate after death in adult salmon. Considering the life cycle of C. shasta and anadromous salmon, the parasite may have evolved 2, non-mutually exclusive developmental strategies. In young fish (parr and smolts), the parasite sporulates shortly after infection and is released into freshwater from either live or dead fish before their migration to seawater, where the alternate host is absent. The second strategy occurs in adult salmon, particularly spring Chinook salmon, which become infected upon their return to freshwater in the spring or early summer. For several months throughout the summer, only prespore stages are observed in most fish, even at the time of spawning. But once the fish dies, environmental conditions experienced by C. shasta change and viable presporogonic stages are induced to sporulate. As the post-spawned fish occur in the upper reaches of rivers, the myxospores would be released in a freshwater environment that would provide a reasonable opportunity for them to encounter their freshwater polychaete hosts, which reside downstream.

Body morphology of juvenile Chinook salmon Oncorhynchus tshawytscha in the upper Willamette River, Oregon, U.S.A., was analysed to determine if variation in body shape is correlated with migratory life-history tactics followed by juveniles. Body shape was compared between migrating juveniles that expressed different life-history tactics, i.e. autumn migrants and yearling smolts, and among parr sampled at three sites along a longitudinal river gradient. In the upper Willamette River, the expression of life-history tactics is associated with where juveniles rear in the basin with fish rearing in downstream locations generally completing ocean ward migrations earlier in life than fish rearing in upstream locations. The morphological differences that were apparent between autumn migrants and yearling smolts were similar to differences between parr rearing in downstream and upstream reaches, indicating that body morphology is correlated with life-history tactics. Autumn migrants and parr from downstream sampling sites had deeper bodies, shorter heads and deeper caudal peduncles compared with yearling smolts and parr from the upstream sampling site. This study did not distinguish between genetic and environmental effects on morphology; however, the results suggest that downstream movement of juveniles soon after emergence is associated with differentiation in morphology and with the expression of life-history variation., (© 2014 The Fisheries Society of the British Isles.)

The Pacific salmonid species Oncorhynchus mykiss is separated into a migratory form (steelhead trout) and a non-migratory form (rainbow trout). A decrease in water temperature is likely a cue triggering downstream behavior in the migratory form, and testosterone inhibits onset of this behavior. To elucidate differences in sensitivity to water temperature decreases between the migratory and non-migratory forms and effect of testosterone on the sensitivity, we examined two experiments. In experiment 1, we compared changes in body temperature during a short-term decrease in water temperature between both live and dead steelhead and rainbow trout. In experiment 2, we investigated effects of testosterone on body temperature decrease in steelhead trout. Water temperature was decreased by 3°C in 30min. The body temperature of the steelhead decreased faster than that of the rainbow trout. In contrast, there was no significant difference in the decrease in body temperature between dead steelhead and rainbow trout specimens. The body temperature of the testosterone-treated steelhead trout decreased more slowly than that of control fish. Our results suggest that the migratory form is more sensitive to decreases in water temperature than the non-migratory form. Moreover, testosterone might play an inhibitory role in sensitivity to such decreases., (Copyright © 2013 Elsevier Inc. All rights reserved.)

Histology is often underutilized in aquatic animal disease screening and diagnostics. The agreement between histological classifications of infection and results using diagnostic testing from the American Fisheries Society's Blue Book was conducted with 4 common salmon pathogens: Aeromonas salmonicida, Renibacterium salmoninarum, Ceratomyxa shasta, and Nanophyetus salmincola. Adult Chinook salmon (Oncorhynchus tshawytscha) in Oregon were evaluated, and agreement between tests was calculated. Live and dead (both pre- and postspawning) salmon were collected from the Willamette River, Oregon, its tributaries, the Willamette Hatchery, and after holding in cool, pathogen-free water during maturation at Oregon State University. Sensitivity and specificity of histology compared to Blue Book methods for all fish, live fish only, and dead (pre- and postspawned combined) fish only were, respectively, as follows: A. salmonicida (n = 105): specificity 87.5%, 87.5%, 87.5% and sensitivity 38.6%, 14.8%, 60.0%; R. salmoninarum (n = 111): specificity 91.9%, 85.7%, 97.7% and sensitivity 16.0%, 7.1%, 27.2%; C. shasta (n = 136): specificity 56.0%, 63.3%, 28.6% and sensitivity 83.3%, 86.2%, 71.4%; N. salmincola (n = 228): specificity 68.2%, 66.7%, not possible to calculate for dead fish and sensitivity 83.5%, 80.5%, 87.3%. The specificity was good for bacterial pathogens. This was not the case for C. shasta, likely due to detection of presporogenic forms only by histology. Sensitivity of histology for bacterial pathogens was low with the exception of dead fish with A. salmonicida. Kappa analysis for agreement between Blue Book and histology methods was poor to moderate. However, histological observations revealed the presence of other pathogens that would not be detected by other methods.

A Sebastes-specific complementary DNA (cDNA) microarray was developed to identify potential biomarkers involved in the capture stress and recovery of Sebastes species if they are assisted in returning to their original depth of capture following barotrauma. Black rockfish Sebastes melanops were exposed to simulated decompression from 450 kPa (c. 35 m depth) (which resulted in barotrauma) and subsequent recompression. Sebastes melanops were sampled for liver tissue at days 3, 15 and 31 post-barotrauma. Potential candidate genes were identified from the microarray and then quantitative real-time PCR (qrt-PCR) was used to validate expression levels in biological replicates. Six potential biomarkers associated with the innate immune system were identified that were up-regulated in liver tissue at 3 days post-barotrauma: complement C1q-like protein 2, complement component C3, complement regulatory plasma protein, serum amyloid A-5, c-type lysozyme and hepcidin precursor type I. In addition, complement c1q was correlated to the presence of a ruptured swimbladder, providing further support that this gene may be a good biomarker of injury and recovery. Immune genes were no longer up-regulated at day 31 post-barotrauma, a good indication of recovery in S. melanops., (© 2012 The Authors. Journal of Fish Biology © 2012 The Fisheries Society of the British Isles.)

Overfished species of rockfish, Sebastes spp., from the Northeast Pacific experience high bycatch mortality because of 'barotrauma', a condition induced from the rapid change in pressure during capture. Field experiments show that it may be possible for rockfish to recover from barotrauma if quickly recompressed; however, no work has followed the physiological recovery of rockfish after recompression or determined whether it is possible for rockfish to survive barotrauma in the long term. Barotrauma was induced in adult black rockfish, Sebastes melanops Girard, from a simulated depth of 35 m, followed by recompression. Blood and selected tissues (eye, heart ventricle, head kidney, liver, rete mirabile and gonad) were sampled at days 3, 15 and 31 post-recompression to evaluate the tissue- and physiologic-level response during recovery. No mortality from barotrauma occurred during the experiments, and feeding resumed in 80% of both treatment and control fish. The primary injury in treatment fish was the presence of a ruptured swimbladder and/or a ruptured tunica externa (outer layer of swimbladder), which was slow to heal. Blood plasma was analysed for glucose, sodium, chloride, potassium, calcium, phosphorus, insulin-like growth factor-1 and cortisol. Plasma analyses indicated no strong effects because of barotrauma, suggesting overall handling stress outweighed any effect from barotrauma. Rockfish with ruptured swimbladders may face compromised competency in the wild; however, it appears the majority of black rockfish decompressed from 35 m have a high potential for recovery if recompressed immediately after capture. This research suggests recompression could be a valuable bycatch mortality reduction tool for rockfish in recreational fisheries., (© 2012 Blackwell Publishing Ltd.)

There is some concern that incidental consumption of eggs cured with commercially available cures for the purpose of sport fishing causes mortality in juvenile salmon. We evaluated this by feeding juvenile spring Chinook (Oncorhynchus tshawytscha) and steelhead (O. mykiss) with eggs cured with one of five commercially available cures. We observed significant levels of mortality in both pre-smolts and smolts. Depending on the experiment, 2, 3, or 4 of the cures were associated with mortality. Mortality tended to be higher in the smolts than in the parr, but there was no clear species effect. The majority of mortality occurred within the first 10 d of feeding. Removal of sodium sulfite from the cure significantly reduced the level of mortality. Soaking the eggs prior to feeding did not reduce mortality. We observed a clear relationship between the amount of cured egg consumed each day and the survival time. We conclude that consumption of eggs cured with sodium sulfite has the potential to cause mortality in juvenile steelhead and Chinook salmon in the wild.

We evaluated the ability of 5 muscle- or skin-dwelling parasites to persist in naturally infected coho salmon, Oncorhynchus kisutch, from the West Fork Smith River, Oregon, by holding them in captivity from late summer to early spring (parr stage to the typical time of smoltification). These parasites included metacercariae of 3 digeneans, Nanophyetus salmincola, Apophallus sp., and neascus sp., and 2 myxozoans, Myxobolus insidiosus and Myxobolus fryeri. Two groups of wild-caught fish were evaluated in the laboratory, i.e., heavily infected fish from the lower main stem and less severely infected fish collected from tributaries of this river. All parasites survived in these fish for the 7-month experiment. Only 2 parasites had a statistically significant lower median abundance between host life stages. The mean abundance of N. salmincola declined 45% in the tributary fish and Apophallus sp. declined 43% in the lower main stem fish. However, more than 50% of each species persisted until the end of the study, with smolts still harboring relatively high infections.

This paper is a review of the effects of stress on reproduction in fishes. I hope to further the development of the concepts of allostasis and hormesis as relevant to understanding reproduction in general and in fish in particular. The main contentions I derive in this review are the following: Stressors affect fish reproduction in a variety of ways depending on the nature and severity of the stressor. The effects are transduced through a hormonal cascade initiated by perception of the stressor and involving the hypothalamus-pituitary-interrenal axis, the catecholamines, and also cytokines. Mounting a stress response and resisting a stressor is an energetically costly process, including costs associated with allostasis, attempting to reset homeostatic norms. Responses in emergency situations (e.g., being chased by a predator or a net) can be different from those where fish can cope (e.g., being in a more crowded environment) with a stressor, but both situations involve energy re-budgeting. Emergency responses happen in concert with the onset of energy limitations (e.g., the fish may not eat), while coping with allostatic overload can happen in a more energy-rich environment (e.g., the fish can continue to eat). Low levels of stress may have a positive effect on reproductive processes while greater stress has negative effects on fish reproduction. The concept of hormesis is a useful way to think about the effect of stressors on fish reproduction since responses can be nonmonotonal, often biphasic., (Published by Elsevier Inc.)

Zebrafish, Danio rerio , are frequently handled during husbandry and experimental procedures in the laboratory, yet little is known about the physiological responses to such stressors. We measured the whole-body cortisol levels of adult zebrafish subjected to net stress and air exposure at intervals over a 24 h period; cortisol recovered to near control levels by about 1 h post-net-stress (PNS). We then measured cortisol at frequent intervals over a 1 h period. Cortisol levels were more than 2-fold higher in net stressed fish at 3 min PNS and continued to increase peaking at 15 min PNS, when cortisol levels were 6-fold greater than the control cortisol. Mean cortisol declined from 15 to 60 min PNS, and at 60 min, net-stressed cortisol was similar to control cortisol. Because the age of fish differed between studies, we examined resting cortisol levels of fish of different ages (3, 7, 13, and 19 months). The resting cortisol values among tanks with the same age fish differed significantly but there was no clear effect of age. Our study is the first to report the response and recovery of cortisol after net handling for laboratory-reared zebrafish.

Mycobacteria are significant pathogens of laboratory zebrafish, Danio rerio (Hamilton). Stress is often implicated in clinical disease and morbidity associated with mycobacterial infections but has yet to be examined with zebrafish. The aim of this study was to examine the effects of husbandry stressors on zebrafish infected with mycobacteria. Adult zebrafish were exposed to Mycobacterium marinum or Mycobacterium chelonae, two species that have been associated with disease in zebrafish. Infected fish and controls were then subjected to chronic crowding and handling stressors and examined over an 8-week period. Whole-body cortisol was significantly elevated in stressed fish compared to non-stressed fish. Fish infected with M. marinum ATCC 927 and subjected to husbandry stressors had 14% cumulative mortality while no mortality occurred among infected fish not subjected to husbandry stressors. Stressed fish, infected with M. chelonae H1E2 from zebrafish, were 15-fold more likely to be infected than non-stressed fish at week 8 post-injection. Sub-acute, diffuse infections were more common among stressed fish infected with M. marinum or M. chelonae than non-stressed fish. This is the first study to demonstrate an effect of stress and elevated cortisol on the morbidity, prevalence, clinical disease and histological presentation associated with mycobacterial infections in zebrafish. Minimizing husbandry stress may be effective at reducing the severity of outbreaks of clinical mycobacteriosis in zebrafish facilities.

We evaluated the direct effects of in vitro exposures to tributyltin (TBT), a widely used biocide, on the cell-mediated immune system of Chinook salmon (Oncorhynchus tshawytscha). Splenic and pronephric leukocytes isolated from juvenile Chinook salmon were exposed to TBT (0, 0.1, 0.2, 0.3, 0.4, 0.5, and 0.6 mg/l) in cell cultures for 24 h. Effects of TBT on cell viability, induction of apoptosis, and mitogenic responses were measured by flow cytometry. Splenic and pronephric leukocytes in the presence of TBT experienced a concentration-dependent decrease in viability in cell cultures. Apoptosis was detected as one of the mechanisms of cell death after TBT exposure. In addition, pronephric lymphocytes exhibited a greater sensitivity to TBT exposure than pronephric granulocytes. The functional ability of splenic B-cells to undergo blastogenesis upon lipopolysaccharide stimulation was also significantly inhibited in the presence of 0.05, 0.07, or 0.10 mg/l of TBT in the cell cultures. Flow cytometric assay using a fluorescent conjugated monoclonal antibody against salmon surface immunoglobulin was employed for the conclusive identification of B-cells in the Chinook salmon leukocytes. Our findings suggest that adverse effects of TBT on the function or development of fish immune systems could lead to an increase in disease susceptibility and its subsequent ecological implications.

Organochlorine (OC) pesticide concentrations in blood plasma samples from 88 juvenile white sturgeon collected from the lower Columbia River were measured and compared to plasma sex steroid and OC tissue levels previously measured in corresponding fish. Significant squared correlation coefficients between summation operator DDT concentrations in sturgeon plasma and gonads and livers were 0.37 and 0.32, respectively. Significant negative correlations between plasma testosterone concentration and plasma Sigma DDT concentration in male fish (r(2)=0.26), plasma 17beta estradiol concentration and plasma Sigma DDT concentration in female fish (r(2)=0.38) and condition factor and plasma Sigma DDT concentration in all fish were found (r(2)=0.17). These results suggest that blood plasma may be a suitable nondestructive method for monitoring adult sturgeon population for persistent OC contaminants.

Influence of environmental salinity on expression of distinct corticosteroid receptor (CR) genes, glucocorticoid receptor (GR)-1 and -2, and mineralcorticoid receptor (MR), was examined in osmoregulatory and hemopoietic organs and leucocytes of steelhead trout (Oncorhynchus mykiss). There was no significant difference in plasma cortisol levels between freshwater (FW)- or seawater (SW)-acclimated trout, whereas Na+, K+-ATPase was activated in gill of SW fish. Plasma lysozyme levels also showed a significant increase after acclimation to SW. In SW-acclimated fish, mRNA levels of GR-1, GR-2, and MR were significantly higher in gill and body kidney than those in FW. Head kidney and spleen showed no significant change in these CR mRNA levels after SW-acclimation. On the other hand, leucocytes isolated from head kidney and peripheral blood showed significant decreases in mRNA levels of CR in SW-acclimated fish. These results showed differential regulation of gene expression of CR between osmoregulatory and immune systems.

Concentrations of polybrominated diphenyl ethers (PBDEs), pesticides, polychlorinated biphenyls (PCBs), and polycyclic aromatic hydrocarbons were measured in 136 fish from 14 remote lakes in 8 western U.S. National Parks/Preserves between 2003 and 2005 and compared to human and wildlife contaminant health thresholds. A sensitive (median detection limit--18 pg/g wet weight), efficient (61% recovery at 8 ng/g), reproducible (4.1% relative standard deviation (RSD)), and accurate (7% deviation from standard reference material (SRM)) analytical method was developed and validated for these analyses. Concentrations of PCBs, hexachlorobenzene, hexachlorocyclohexanes, DDTs, and chlordanes in western U.S. fish were comparable to or lower than mountain fish recently collected from Europe, Canada, and Asia. Dieldrin and PBDE concentrations were higher than recent measurements in mountain fish and Pacific Ocean salmon. Concentrations of most contaminants in western U.S. fish were 1-6 orders of magnitude below calculated recreational fishing contaminant health thresholds. However, lake average contaminant concentrations in fish exceeded subsistence fishing cancer thresholds in 8 of 14 lakes and wildlife contaminant health thresholds for piscivorous birds in 1 of 14 lakes. These results indicate that atmospherically deposited organic contaminants can accumulate in high elevation fish, reaching concentrations relevant to human and wildlife health.

Mercury accumulation in aquatic foodwebs and its effects on aquatic biota are of growing concern both for the health of the fish and the piscivores that prey upon them. This is of particular concern for western U.S. National Parks because it is known that mountainous and Arctic areas are sinks for some contaminants. The Western Airborne Contaminants Assessment Project seeks, in part, to ascertain mercury concentrations and evaluate effects of contaminants on biota in 14 lakes from 8 National Parks or Preserves. In this paper we report that mercury has accumulated to concentrations in troutthat may negatively impact some piscivorous wildlife, indicating potential terrestrial ecosystem effects. Additionally, we show that mercury concentrations increase with age in 4 species of trout, providing evidence of bioaccumulation. Finally, we demonstrate that mercury is associated with tissue damage in the kidney and spleen, as indicated by increases in macrophage aggregates. This finding suggests that mercury, and possibly other contaminants, are Macrophage aggregates suggests that mercury, a negatively affecting the trout that inhabit these remote and protected ecosystems. Our results indicate that mercury is indeed a concern for the U.S. National Parks, from an organismic and potentially an ecosystem perspective.

To better appreciate the mechanisms underlying the physiology of the stress response, an oligonucleotide microarray and real-time RT-PCR (QRT-PCR) were used to study gene expression in the livers of rainbow trout (Oncorhynchus mykiss). For increased confidence in the discovery of candidate genes responding to stress, we conducted two separate experiments using fish from different year classes. In both experiments, fish exposed to a 3 h stressor were compared to control (unstressed) fish. In the second experiment some additional fish were exposed to only 0.5 h of stress and others were sampled 21 h after experiencing a 3 h stressor. This 21 h post-stress treatment was a means to study gene expression during recovery from stress. The genes we report as differentially expressed are those that responded similarly in both experiments, suggesting that they are robust indicators of stress. Those genes are a major histocompatibility complex class 1 molecule (MHC1), JunB, glucose 6-phosphatase (G6Pase), and nuclear protein 1 (Nupr1). Interestingly, Nupr1 gene expression was still elevated 21 h after stress, which indicates that recovery was incomplete at that time.

Compared to teleosts, little is known about the stress response in chondrosteans, and the glucocorticoid(s) most responsive to stress have never been definitively determined in sturgeon. In terms of cortisol production, pallid sturgeon (Scaphirhynchus albus) have a low physiological response to stress compared to other sturgeons (Acipenser s.p.). Because of this, our null hypothesis was that cortisol is not the predominant glucocorticoid secreted in response to stress in pallid sturgeon. Our objective was to identify the putative glucocorticoids present in the plasma of pallid sturgeon during the stress response. Pallid sturgeon were subjected to a severe confinement stress (12 h) with an additional handling stressor for the first 6 h. Control fish were not subjected to confinement but were handled only to collect blood. Blood plasma was collected at time 0, 6, and 12 h. Gas chromatography/mass spectrometry was used to screen the plasma for the spectrum of glucocorticoids and determine the putative steroid secreted during the stress response. Cortisol was the primary glucocorticoid detected in stressed pallid sturgeon. In addition, the cortisol metabolites cortisone, alloTHE (5alpha-pregnane-3alpha,17alpha,21-triol-11,20-dione), allo-alpha-cortolone (3alpha,17alpha,20alpha,21-tetrahydro-5alpha-pregnan-11-one), and allo-beta-cortolone (3alpha,17alpha,20beta,21-tetrahydro-5alpha-pregnan-11-one) were detected. Plasma cortisol increased from a resting concentration of 0.67 ng/ml to 10.66 ng/ml at 6h followed by a decrease to 6.78 ng/ml by 12 h. Plasma glucose increased significantly by time 6 and 12 h in both stressed and unstressed groups and remained elevated at time 12h, while resting lactate concentrations were low to non-detectable and did not increase significantly with the stressor over time. Cortisol was the primary glucocorticoid synthesized and secreted in response to a stressor in pallid sturgeon. Though the proportional increase in plasma cortisol in stressed pallid sturgeon was lower than many other species of sturgeon, the concentration was high enough to elicit a secondary stress response as seen by changes in plasma glucose.

The present study investigated: 1) the behavioral effects of chronic administration of a serotonin uptake inhibitor (fluoxetine) in juvenile Chinook salmon, Oncorhynchus tshawytscha and, 2) whether chronic administration of fluoxetine alters the behavioral effects of corticotropin-releasing hormone (CRH). Chronic (20 day) treatment with fluoxetine decreased locomotor activity when compared to fish given long-term injections of saline. An intracerebroventricular (i.c.v.) injection of CRH had no effect on locomotor activity following a 20 day intraperitoneal treatment with either saline or fluoxetine. Chronic treatment with fluoxetine also increased the amount of time fish spent near the center of the tank. A similar increase was seen in fish given a chronic intraperitoneal (i.p.) series of saline followed by an acute i.c.v. injection of CRH. However, the effect was not additive when fish were given chronic i.p. injections of fluoxetine followed by an acute i.c.v. injection of CRH. These results provide evidence to support the hypothesis that the serotonergic system is involved in mediating locomotor activity and habitat choice in teleosts.

Juvenile steelhead (Oncorhynchus mykiss) acclimated to freshwater (FW) were subjected for 3 h to confinement stress in FW, and subsequently saltwater (SW, 25 ppt) was introduced to all tanks. Fish were sampled immediately after the stress treatment, and 1, 7, and 14 days after introduction of SW. Electrolytes, cortisol, glucose, and lactate showed the typical stress response expected after stress treatment in FW. Fish regained osmotic balance within 24 h. Glucose concentrations were increasing throughout the experiment and lactate levels stayed elevated during the time spent in SW. Insulin-like growth factor-1 (IGF-1) did not show an immediate response to stress but after transfer to SW we detected significantly higher concentrations for control fish at days 1 and 14. The differences in IGF-1 levels between stressed and control fish are not reflected in SW adaptability but positive correlations between IGF-1 and electrolyte levels in control fish may indicate its role for osmoregulation. Confinement stress did not impair feed intake subsequently in SW, but our results suggest that feed intake was suppressed by the change of the media from FW to SW.

This study determined the partitioning of total mercury in liver, gonad, and cheek muscle of white sturgeon (Acipenser transmonatus) in the lower Columbia River. The relationship between tissue mercury concentrations and various physiologic parameters was assessed. White sturgeon were captured in commercial fisheries in the estuary and Bonneville, The Dalles, and John Day Reservoirs. Condition factor (CF), relative weight (Wr), and gonadosomatic index (GSI) were determined for each fish (n = 57). Gonadal tissue was examined histologically to determine sex and stage of maturity. Liver (n = 49), gonad (n = 49), and cheek muscle (n = 57) were analyzed for total mercury using cold-vapor atomic fluorescence spectrophotometry. Tissue protein concentrations were measured by ultraviolet-visible spectroscopy. Plasma was analyzed for testosterone (T), 11-ketotestosterone (KT), and 17ss-estradiol (E2) using radioimmunoassay. Mean tissue mercury concentrations were higher in muscle compared with liver and gonad at all sampling locations, except Bonneville Reservoir where mean liver mercury content was the highest tissue concentration observed in the study. Significant negative correlations between plasma androgens (T and KT) and muscle mercury content and plasma E2 and liver mercury content were found. A significant positive linear relationship between white sturgeon age and liver mercury concentrations was evident. Significant negative correlations between CF and relative weight and gonad and liver mercury content were found. In addition, immature male sturgeon with increased gonad mercury content had decreased GSIs. These results suggest that mercury, in the form of methylmercury, may have an effect on the reproductive potential of white sturgeon.

p,p'-DDE, the main metabolite of DDT, is still detected in aquatic environments throughout the world. Here, the effects and mechanisms by which p,p'-DDE exposure might affect the immune system of chinook salmon (Oncorhynchus tshawytscha) was studied. Isolated salmon splenic and pronephric leukocytes were incubated with different concentrations of p,p'-DDE, and cell viability, induction of apoptosis, and mitogenic responses were measured by flow cytometry and Alamar Blue assay. p,p'-DDE significantly reduced cell viability and proliferation and increased apoptosis. The effect of p,p'-DDE on pronephric leukocytes was more severe than on splenic leukocytes, likely because pronephric leukocytes had a higher proportion of granulocytes, cells that appear more sensitive to p,p'-DDE. The effect of p,p'-DDE on leukocytes appeared to vary between developmental stages or seasonal differences. The mitogenic response of leukocytes of chinook salmon exposed to p,p'-DDE in vivo exhibited a biphasic dose-response relationship. Only leukocytes isolated from salmon treated with 59 ppm p,p'-DDE had a significantly lower percentage of Ig+ blasting cells than controls, although the response was biphasic. These results support the theory that exposure to chemical contaminants could lead to an increase in disease susceptibility and mortality of fish due to immune suppression.

Extrapituitary expression of the growth hormone (GH) gene has been reported for the immune system of various vertebrates. In the rainbow trout (Oncorhynchus mykiss), GH mRNA could be detected in several lymphoid organs and leucocytes by reverse transcriptase-polymerase chain reaction (RT-PCR). To understand the control of GH expression in the fish immune system, mRNA levels for two distinct GH genes (GH1 and GH2) in trout leucocytes isolated from peripheral blood were quantified using a real-time PCR method. Both GH mRNAs could be detected in trout leucocytes, although their levels were extremely low compared to those in pituitary cells. The levels of GH2 mRNA in leucocytes were several times higher than those of GH1, while no difference was observed between GH1 and GH2 mRNA levels in the pituitary. Administration of dibutyryl cyclic AMP and cortisol produced a significant elevation of GH mRNA levels in trout leucocytes, although the levels were unchanged by T3. GH1 and GH2 mRNA levels showed similarities in responses to those factors. The effect of cortisol on GH mRNA appears biphasic; a dose-depending elevation of GH gene expression was observed in leucocytes treated with cortisol at below 200 nM, however, cortisol had no effect at 2000 nM. Cortisol-treated leucocytes showed no significant change in the mRNA level of beta-actin or proliferative activity during the experiments. Our results thus show that, at the low levels, GH gene expression in trout leucocytes is regulated by cortisol, which has been known as a regulatory factor of GH gene expression in pituitary cells, and suggest a physiological significance of paracrine GH produced in the fish immune system.

We evaluated the effect of corticotropin-releasing hormone (CRH) on spatial distribution and downstream movement in an artificial stream in juvenile Chinook salmon (Oncorhynchus tshawytscha) during the period when the fish were able to tolerate seawater. An intracerebroventricular (ICV) injection of CRH (500 ng) to hatchery fish significantly increased the proportion of fish that were distributed downstream of a mid-stream release site. A second group of hatchery fish were given ICV injections of saline (control) or CRH (500 ng) and released near the top of the stream. The time taken to enter a trap at the lower end of the stream was recorded. In all cases the groups given CRH had a higher proportion of fish that did not enter the trap within 60 min of release. However, in those fish that did enter the trap, treatment with CRH increased the speed of downstream movement to this point relative to control fish. Wild sub-yearling Chinook salmon were captured during their downstream migration to the estuary and given ICV injections of saline or CRH (500 ng) either 2, 3, or 7 days after transport from the river. As with hatchery fish, a significantly higher proportion of wild fish that were administered CRH did not enter the trap at the lower end of the stream. The mean time of passage for control fish decreased on each successive day (day 2 > day 3 > day 7). In contrast, the mean passage time of the wild fish that were given CRH was relatively constant through time, and was only significantly faster than control fish on day 2. The current study provides evidence that CRH alters the downstream movement of juvenile Chinook in a simulated stream environment, and produces behavioral effects similar to those of juvenile salmonids that are stressed during their downstream migration.

The in vitro effects of prolactin (PRL) and growth hormone (GH) on the proliferation and survival of leucocytes isolated from the blood of the rainbow trout (Oncorhynchus mykiss) were examined, with special reference to the immunosuppression by cortisol. Both PRL and GH induced a mitogenic effect in trout leucocytes. Contrary, the frequencies of annexin V-positive apoptotic cells and propidium iodide-positive dead cells were decreased by the administration of PRL, but were uninfluenced by GH. Administration of cortisol suppressed the mitotic activity and induced cell death of leucocytes. PRL inhibited the decrease in mitosis and the increase in cell death due to cortisol. GH significantly assisted recovery of cortisol-suppressed mitosis but did not influence the survival of leucocytes. These results suggest that PRL and GH are involved in the maintenance of specific immune functions in fish through a prevention of immunosuppression by cortisol.

The authors examined the control of locomotor activity in juvenile salmon (Oncorhynchus tshawytscha) by manipulating 3 neurotransmitter systems--gamma-amino-n-butyric acid (GABA), dopamine, and serotonin--as well as the neuropeptide corticotropin releasing hormone (CRH). Intracerebroventricular (ICV) injections of CRH and the GABAA agonist muscimol stimulated locomotor activity. The effect of muscimol was attenuated by administration of a dopamine receptor antagonist, haloperidol. Conversely, the administration of a dopamine uptake inhibitor (4',4"-difluoro-3-alpha-[diphenylmethoxy] tropane hydrochloride [DUI]) potentiated the effect of muscimol. They found no evidence that CRH-induced hyperactivity is mediated by dopaminergic systems following concurrent injections of haloperidol or DUI with CRH. Administration of muscimol either had no effect or attenuated the locomotor response to concurrent injections of CRH and fluoxetine, whereas the GABAA antagonist bicuculline methiodide potentiated the effect of CRH and fluoxetine.