Saprolegnia infection after vaccination in Atlantic salmon is associated with differential expression of stress and immune genes in the host

This study assessed the impact of routine vaccination of Atlantic salmon pre-smolts on gene expression and the possible link to saprolegniosis on Scottish fish farms. Fish were in 4 different groups 1) 'control' - fish without handling or vaccination 2) 'vaccinated' - fish undergoing full vaccination procedure 3) 'non vaccinated' - fish undergoing full vaccination procedure but not vaccinated and 4) 'vaccinated-MH' - fish undergoing vaccination, but procedure involved minimal handling. A strong increase in cortisol and glucose levels was observed after 1 h in all groups relative to the control group. Only in the non-vaccinated group did the level decrease to near control levels by 4 h. Expression levels of six stress marker genes in general for all groups showed down regulation over a 9-day sampling period. In contrast, expression levels for immune response genes in the head kidney showed significant up-regulation for all eight genes tested for both vaccinated groups whereas the non-vaccinated group showed up-regulation for only MHC-II and IL-6b in comparison to the control. Both the vaccination procedure and the administration of the vaccine itself were factors mediating changes in gene expression consistent with fish being susceptible to natural occurring saprolegniosis following vaccination.

Corticosterone mediates telomere length in raptor chicks exposed to chemical mixture

Stressors experience early in life by animals may have carry over impacts on life-traits over the life cycle. Accelerated telomere attrition induced by stress during development and growth could play a role in such delayed effects. Among stressors, exposure to chemicals may modify telomere dynamic but, to date, the trends evidenced between exposure and telomere shortening remains inconsistent. Moreover, the role of corticosterone as a possible mediator of chemical impact on telomere is not yet clearly established. Here, we investigated in wild populations of Red kite whether nestling exposure to metals and pesticides was related to corticosterone concentrations in feathers and telomere length measured in 47 individuals. Lead and mercury concentrations in blood ranged from 2.3 to 59.0 µg L^-1 and to 1.4 to 115.7 µg L^-1, respectively, and were below the toxicity thresholds proposed for wildlife. Rodenticides were detected in 30% of the chicks. Corticosterone increased with mercury and lead in interaction, showing a synergistic effect of these 2 non-essential metals on this stress hormone. Telomere length was not linked to metals and/or rodenticide exposure while it was related negatively to corticosterone. The relationship between telomere and corticosterone was modulated by nestling's age, which suggests that the rate of telomere shortening is higher when corticosterone increases. Our findings propose an effect of low exposure of Red Kite nestlings to mercury and lead mixture to raise baseline corticosterone in feathers. The relationships established suggest the hypothesis that telomere attrition could be an indirect consequence of metal exposure mediated by corticosterone.

Immunoassays are not immune to errors: Examples from two studies of steroid output from freshwater trout farms

A "reproducibility crisis" is widespread across scientific disciplines, where results and conclusions of studies are not supported by subsequent investigation. Here we provide a steroid immunoassay example where human errors generated unreproducible results and conclusions. Our study was triggered by a scientific report citing abnormally high concentrations (means of 4-79 ng L^-1) of three natural sex steroids [11-ketotestosterone (11-KT), testosterone (T) and oestradiol (E2)] in water samples collected from two UK rivers over 4 years (2002-6). Furthermore, the data suggested that trout farms were a major source because reported steroid concentrations were 1.3-6 times higher downstream than upstream. We hypothesised that the reported levels were erroneous due to substances co-extracted from the water causing matrix effects (i.e. "false positives") during measurement by enzyme-linked immunoassay (EIA). Thus, in collaboration with three other groups (including the one that had conducted the 2002-6 study), we carried out field sampling and assaying to examine this hypothesis. Water samples were collected in 2010 from the same sites and prepared for assay using an analogous method [C18 solid phase extraction (SPE) followed by extract clean-up with aminopropyl SPE]. Additional quality control ("spiked" and "blank") samples were processed. Water extracts were assayed for steroids using radioimmunoassay (RIA) as well as EIA. Although there were statistically significant differences between EIA and RIA (and laboratories), there was no indication of matrix effects in the EIAs. Both the EIAs and RIAs (uncorrected for recovery) measured all three natural steroids at <0.6 ng L^-1 in all river water samples, indicating that the trout farms were not a significant source of natural steroids. The differences between the two studies were considerable: E2 and T concentrations were ca. 100-fold lower and 11-KT ca. 1000-fold lower than those reported in the 2002-6 study. In the absence of evidence for any marked changes in husbandry practice (e.g. stock, diet) or environmental conditions (e.g. water flow rate) between the study periods, we concluded that calculation errors were probably made in the first (2002-6) study associated with confusion between extract and water sample concentrations. The second (2010) study also had several identified examples of calculation error (use of an incorrect standard curve; extrapolation below the minimum standard; confusion of assay dilutions during result work-up; failure to correct for loss during extraction) and an example of sample contamination. Similar and further errors have been noted in other studies. It must be recognised that assays do not provide absolute measurements and are prone to a variety of errors, so published steroid levels should be viewed with caution until independently confirmed.

Effects of temperature on amoebic gill disease development: Does it play a role?

A relationship between increasing water temperature and amoebic gill disease (AGD) prevalence in Atlantic salmon (Salmo salar) has been noted at fish farms in numerous countries. In Scotland (UK), temperatures above 12°C are considered to be an important risk factor for AGD outbreaks. Thus, the purpose of this study was to test for the presence of an association between temperature and variation in the severity of AGD in Atlantic salmon at 10 and 15°C. The results showed an association between temperature and variation in AGD severity in salmon from analysis of histopathology and Paramoeba perurans load, reflecting an earlier and stronger infection post-amoebae exposure at the higher temperature. While no significant difference between the two temperature treatment groups was found in plasma cortisol levels, both glucose and lactate levels increased when gill pathology was evident at both temperatures. Expression analysis of immune- and stress-related genes showed more modulation in gills than in head kidney, revealing an organ-specific response and an interplay between temperature and infection. In conclusion, temperature may not only affect the host response, but perhaps also favour higher attachment/growth capacity of the amoebae as seen with the earlier and stronger P. perurans infection at 15°C.

The Influence of Sex, Parasitism, and Ontogeny on the Physiological Response of European Eels (Anguilla anguilla) to an Abiotic Stressor

Migration of adult European eels (Anguilla anguilla) from freshwater feeding grounds to oceanic spawning grounds is an energetically demanding process and is accompanied by dramatic physiological and behavioral changes. Humans have altered the aquatic environment (e.g., dams) and made an inherently challenging migration even more difficult; human activity is regarded as the primary driver of the collapse in eel populations. The neuroendocrine stress response is central in coping with these challenging conditions, yet little is known about how various biotic factors such as sex, parasites, and ontogeny influence (singly and via interactions) the stress response of eels. In this study, mixed-effects and linear models were used to quantify the influence of sex, parasitism (Anguillicola crassus), life stage (yellow and silver eels), and silvering stage on the stress response of eels when exposed to a standardized handling stressor. The physiological response of eels to a standardized abiotic stressor (netting confinement in air) was quantified through measurements of blood glucose and plasma cortisol. The relationships between biotic factors and the activity of gill Na⁺/K⁺-ATPase was also examined. Analyses revealed that in some instances a biotic factor acted alone while in other cases several factors interacted to influence the stress response. Blood glucose concentrations increased after exposure to the standardized stressor and remained elevated after 4 h. Variation in plasma cortisol concentrations after exposure to the stressor were found to be time dependent, which was exacerbated by life stage and parasitism condition. Males and nonparasitized silver eels had the highest Na⁺/K⁺-ATPase activity. Silvering stage was strongly positively correlated with Na⁺/K⁺-ATPase activity in female eels. Collectively, these findings confirm that the factors mediating stress responsiveness in fish are complicated and that aspects of inherent biotic variation cannot be ignored.

Modulation of the stress response in wild fish is associated with variation in dissolved nitrate and nitrite

Disruption of non-reproductive endocrine systems in wildlife by chemicals has received little attention but represents a potentially significant problem. Nitrate is a major anthropogenic contaminant in the freshwater aquatic environment and has been identified as a potential disrupter of endocrine function in aquatic animals. This study was conducted to investigate the relationship between the function of the neuroendocrine stress axis in fish and inorganic N loading along reaches of rivers receiving cumulative point source and diffuse chemical inputs. To accomplish this, the responsiveness of the stress axis, quantified as the rate of release of cortisol to water across the gills during exposure to a standardised stressor, was measured in three-spined sticklebacks (Gasterosteus aculeatus L.) resident at three sites on each of four rivers in north-west England. The magnitude of the stress response in fish captured at the sites furthest downstream on all rivers was more than twice that of fish captured at upstream sites. Site-specific variation in stress axis reactivity was better explained by between-site variation in concentrations of dissolved nitrate, nitrite, and ammonia than by the concentration of wastewater treatment works effluent. An increase in the magnitude of the stress response was seen among sticklebacks at sites where long-term averaged concentrations of NH₃-N, NO₃-N and NO₂-N exceeded 0.6, 4.0 and 0.1 mg/L respectively. These data suggest that either (i) inorganic N is a better surrogate than wastewater effluent concentration for an unknown factor or factors affecting stress axis function in fish, or (ii) dissolved inorganic N directly exerts a disruptive influence on the function of the neuroendocrine stress axis in fish, supporting concerns that nitrate is an endocrine-modulating chemical.

Long-term water quality data explain interpopulation variation in responsiveness to stress in sticklebacks at both wastewater effluent-contaminated and uncontaminated sites

The magnitude of the corticosteroid response to a standardized stressor varied in proportion to the concentration of effluent in three-spined sticklebacks (Gasterosteus aculeatus L.) captured downstream of 10 wastewater-treatment plants (WWTPs). However, at 9 sites with no upstream WWTP input interpopulation variation in the reactivity of the stress axis occurred across a similar range to that seen for fish at impacted sites, suggesting that the factor(s) responsible for modulating stress responsiveness in sticklebacks is not unique to sites receiving WWTP effluent. Physicochemical data from a long-term monitoring program were employed to investigate whether variation in water quality contributed to between-site variation in stress axis reactivity. Between-site variation in 14 water quality determinands explained between 30% and 60% of the variation in stress reactivity and fish size for sticklebacks at both WWTP-contaminated and uncontaminated sites. At uncontaminated sites the mean mass and length of sticklebacks increased with total oxidized nitrogen (N) concentration (as an indicator of anthropogenic input), whereas at WWTP-contaminated sites fish size decreased with increasing effluent concentration, suggesting that factors adversely affecting growth were present predominantly at WWTP-contaminated sites. In contrast, at both contaminated and uncontaminated sites the magnitude of the corticosteroid response to a standardized stressor increased with anthropogenic input (effluent concentration or total oxidized N, respectively), indicating that a factor or factors modulating the reactivity of the stress axis may be present at both WWTP-contaminated and uncontaminated sites. Environ Toxicol Chem 2016;35:3014-3022. © 2016 SETAC.

A comparison of two methods for the assessment of stress axis activity in wild fish in relation to wastewater effluent exposure

Riverine fish are particularly vulnerable to chemical exposure - rivers receive chemicals of anthropogenic origin from a variety of sources, one of the most significant being the chemically complex effluents discharged by wastewater treatment works (WWTWs). The extent to which non-reproductive components of the endocrine system in fish may be vulnerable to interference by contaminants associated with WWTW effluent is not well understood, but a significant body of evidence does suggest that contaminants present in the aquatic environment may interfere with the normal function of the neuroendocrine stress axis in fish. Field investigations of stress axis function in free-living populations of fish by measurement of hormone concentrations in blood can be confounded by the remoteness of sampling locations and the size of target species. Two methods for assessing stress axis reactivity in situations where blood samples are unavailable were compared in three-spined sticklebacks in relation to their exposure to WWTWs effluent. Sticklebacks were sampled in two successive years at fifteen sites in north-west England impacted by WWTW effluent and the response of each fish to the combined stressor of capture and a brief period of confinement was evaluated using both whole-body immunoreactive cortisol concentrations (WBIC) and the rate of release of cortisol to water (CRTW). A positive relationship between the magnitude of stress-induced CRTW in sticklebacks of both sexes and WWTW effluent concentration at site of capture was observed in both years. However, the relationship between stress-induced WBIC and WWTW effluent concentration was not consistent. These results suggest that components of WWTW effluent can modulate the magnitude of the neuroendocrine stress response in sticklebacks, and by inference in other fish species, but they raise questions about the measurement and interpretation of stress axis responses in fish via endpoints other than blood hormone concentrations. Possible factors underlying the disparity between the CRTW and WBIC results are discussed.

Disruption of the stress response in wastewater treatment works effluent-exposed three-spined sticklebacks persists after translocation to an unpolluted environment

The hypothalamic-pituitary-adrenal/interrenal (HPA/I) axis plays a key role in responding to biotic and abiotic challenges in all vertebrates. Recent studies have shown that the apical response of the HPI axis to stressors in three-spined sticklebacks varies in proportion to the concentration of wastewater treatment works (WWTW) effluent to which the fish are exposed. This study was conducted to determine whether between-site variation in stress responsiveness among WWTW effluent-exposed sticklebacks is persistent or reversible. Sticklebacks from eight sites in north-west England affected by WWTW effluent and exhibiting between-population variation in HPI axis reactivity, were moved to a clean-water aquarium environment. After five months in the contaminant-free environment the responsiveness of these fish to a standardised stressor was determined, by measuring the rate of stress-induced cortisol release across the gills, and compared with the responses of fish newly sampled from the eight original capture sites. Inter-site differences in the reactivity of the HPI axis, proportional to the effluent concentration at each site, persisted among the translocated female sticklebacks for at least 5 months. In male fish however, the direct relationship between stress responsiveness and site-specific effluent was not evident 5 months post-translocation. These results support previous observations that the HPA/I axis, a non-reproductive endocrine system, is vulnerable to modulation by anthropogenic factors in fish and show for the first time that, in female fish at least, this modulation is not transient. The mechanisms underlying these observations, and the implications for the fitness and resilience of affected populations, requires investigation.

Feather corticosterone content in predatory birds in relation to body condition and hepatic metal concentration

This study investigated the feasibility of measuring corticosterone in feathers from cryo-archived raptor specimens, in order to provide a retrospective assessment of the activity of the stress axis in relation to contaminant burden. Feather samples were taken from sparrowhawk Accipiter nisus, kestrel Falco tinnunculus, buzzard Buteo buteo, barn owl Tyto alba, and tawny owl Strix aluco and the variation in feather CORT concentrations with respect to species, age, sex, feather position, and body condition was assessed. In sparrowhawks only, variation in feather CORT content was compared with hepatic metal concentrations. For individuals, CORT concentration (pgmm(-1)) in adjacent primary flight feathers (P5 and P6), and left and right wing primaries (P5), was statistically indistinguishable. The lowest concentrations of CORT were found in sparrowhawk feathers and CORT concentrations did not vary systematically with age or sex for any species. Significant relationships between feather CORT content and condition were observed in only tawny owl and kestrel. In sparrowhawks, feather CORT concentration was found to be positively related to the hepatic concentrations of five metals (Cd, Mn, Co, Cu, Mo) and the metalloid As. There was also a negative relationship between measures of condition and total hepatic metal concentration in males. The results suggest that some factors affecting CORT uptake by feathers remain to be resolved but feather CORT content from archived specimens has the potential to provide a simple effects biomarker for exposure to environmental contaminants.

Quantitative trait loci for magnitude of the plasma cortisol response to confinement in rainbow trout

Better understanding of the mechanisms underlying interindividual variation in stress responses and their links with production traits is a key issue for sustainable animal breeding. In this study, we searched for quantitative trait loci (QTL) controlling the magnitude of the plasma cortisol stress response and compared them to body size traits in five F2 full-sib families issued from two rainbow trout lines divergently selected for high or low post-confinement plasma cortisol level. Approximately 1000 F2 individuals were individually tagged and exposed to two successive acute confinement challenges (1 month interval). Post-stress plasma cortisol concentrations were determined for each fish. A medium density genome scan was carried out (268 markers, overall marker spacing less than 10 cM). QTL detection was performed using qtlmap software, based on an interval mapping method (http://www.inra.fr/qtlmap). Overall, QTL of medium individual effects on cortisol responsiveness (<10% of phenotypic variance) were detected on 18 chromosomes, strongly supporting the hypothesis that control of the trait is polygenic. Although a core array of QTL controlled cortisol concentrations at both challenges, several QTL seemed challenge specific, suggesting that responses to the first and to a subsequent exposure to the confinement stressor are distinct traits sharing only part of their genetic control. Chromosomal location of the steroidogenic acute regulatory protein (STAR) makes it a good potential candidate gene for one of the QTL. Finally, comparison of body size traits QTL (weight, length and body conformation) with cortisol-associated QTL did not support evidence for negative genetic relationships between the two types of traits.

Anti-androgens act jointly in suppressing spiggin concentrations in androgen-primed female three-spined sticklebacks - prediction of combined effects by concentration addition

Increasing attention is being directed at the role played by anti-androgenic chemicals in endocrine disruption of wildlife within the aquatic environment. The co-occurrence of multiple contaminants with anti-androgenic activity highlights a need for the predictive assessment of combined effects, but information about anti-androgen mixture effects on wildlife is lacking. This study evaluated the suitability of the androgenised female stickleback screen (AFSS), in which inhibition of androgen-induced spiggin production provides a quantitative assessment of anti-androgenic activity, for predicting the effect of a four component mixture of anti-androgens. The anti-androgenic activity of four known anti-androgens (vinclozolin, fenitrothion, flutamide, linuron) was evaluated from individual concentration-response data and used to design a mixture containing each chemical at equipotent concentrations. Across a 100-fold concentration range, a concentration addition approach was used to predict the response of fish to the mixture. Two studies were conducted independently at each of two laboratories. By using a novel method to adjust for differences between nominal and measured concentrations, good agreement was obtained between the actual outcome of the mixture exposure and the predicted outcome. This demonstrated for the first time that androgen receptor antagonists act in concert in an additive fashion in fish and that existing mixture methodology is effective in predicting the outcome, based on concentration-response data for individual chemicals. The sensitivity range of the AFSS assay lies within the range of anti-androgenicity reported in rivers across many locations internationally. The approach taken in our study lays the foundations for understanding how androgen receptor antagonists work together in fish and is essential in informing risk assessment methods for complex anti-androgenic mixtures in the aquatic environment.

The stress response of three-spined sticklebacks is modified in proportion to effluent exposure downstream of wastewater treatment works

This study was conducted to investigate whether exposure to wastewater treatment works (WWTW) effluent affects the adaptive stress axis of fish resident within the receiving water. Three-spined sticklebacks (Gasterosteus aculeatus) were sampled from sites downstream of ten WWTWs in north-west England, selected to represent a range of human population equivalents between 1000 and 125,000. Following capture, indices of stress (whole-body cortisol and glucose concentrations) were measured both prior to, and following, the imposition of a standardised stressor to establish both baseline and stress-induced concentrations of cortisol and glucose. There was considerable between-site variation in size, and to a lesser extent condition, of the fish. Pre- and post-stress cortisol and glucose concentrations also varied significantly between-sites. A large proportion of the variation in both the somatic data and the stress response was explained by variation in the proportion of effluent contributing to total river flow at the study sites. Mass (r(2)=0.35, P<0.001) and length (r(2)=0.37, P<0.001) of the fish, and cortisol (r(2)=0.26, P<0.001) and glucose (r(2)=0.12, P<0.01) concentrations in unstressed sticklebacks, were positively related to the concentration of effluent across the sample sites. However, in stressed fish, cortisol (r(2)=0.32, P<0.001) and glucose (r(2)=0.14, P<0.001) concentrations exhibited a negative trend in relation to the effluent concentrations across sites. Individual variation in fish size did not account for the variation in either cortisol or glucose levels. These data provide the first indication that modulation of the stress axis in fish by anthropogenic factors might be widespread and of greater significance than hitherto assumed.

Field surveys reveal the presence of anti-androgens in an effluent-receiving river using stickleback-specific biomarkers

This study was designed to assess whether the removal of endocrine disrupting chemicals (EDCs) and other substances from a Waste Water Treatment Works (WWTW) effluent (receiving water: R. Ray, Swindon, UK) by granular activated carbon (GAC) affected biomarkers of exposure to EDCs [vitellogenin (VTG) and spiggin] in male and female three-spined sticklebacks in the receiving water. A nearby river (R. Ock), with a negligible effluent loading, was used as a control. On each river fish were sampled from four sites on five occasions both before and after remediation of the WWTW effluent. The results show for the first time in a UK field study a clear seasonality of blood VTG concentrations in wild male fish, following closely the VTG profile in female fish from both rivers. VTG levels in male fish from the R. Ray were significantly reduced after the GAC installation. However, VTG levels in males from the control sites also varied significantly across the same period, reducing the significance of this finding. A laboratory exposure to oestradiol (using site-specific lower and upper levels of oestrogenic activity) failed to elevate VTG concentrations in male sticklebacks suggesting that concentrations in the effluent, even prior to remediation, may not have exceeded a critical sensitivity threshold. Most importantly, a significant increase in female kidney spiggin content (a highly specific biomarker of xeno-androgen exposure) occurred in fish in the R. Ray after the GAC installation to levels comparable with those in fish from the control river. The significance of this finding is strengthened by the fact that during the pre-remediation period in the R. Ray, female spiggin levels increased with increasing distance from the WWTW. Our results provide the first in vivo evidence of the presence of anti-androgens in a UK WWTW effluent. To our knowledge this is the first UK-based comprehensive field study on the effects of a WWTW upgrade on biomarkers of EDC exposure using a sentinel fish species and our findings confirm the value of the stickleback as a model species for studying EDCs both in the laboratory and in the wild.

Plasticity of boldness in rainbow trout, Oncorhynchus mykiss: do hunger and predation influence risk-taking behaviour?

Boldness, a measure of an individual's propensity for taking risks, is an important determinant of fitness but is not necessarily a fixed trait. Dependent upon an individual's state, and given certain contexts or challenges, individuals may be able to alter their inclination to be bold or shy in response. Furthermore, the degree to which individuals can modulate their behaviour has been linked with physiological responses to stress. Here we attempted to determine whether bold and shy rainbow trout, Oncorhynchus mykiss, can exhibit behavioural plasticity in response to changes in state (nutritional availability) and context (predation threat). Individual trout were initially assessed for boldness using a standard novel object paradigm; subsequently, each day for one week fish experienced either predictable, unpredictable, or no simulated predator threat in combination with a high (2% body weight) or low (0.15%) food ration, before being reassessed for boldness. Bold trout were generally more plastic, altering levels of neophobia and activity relevant to the challenge, whereas shy trout were more fixed and remained shy. Increased predation risk generally resulted in an increase in the expression of three candidate genes linked to boldness, appetite regulation and physiological stress responses - ependymin, corticotrophin releasing factor and GABA(A) - but did not produce a significant increase in plasma cortisol. The results suggest a divergence in the ability of bold and shy trout to alter their behavioural profiles in response to internal and exogenous factors, and have important implications for our understanding of the maintenance of different behavioural phenotypes in natural populations.

Analysis of stress-induced hepatic gene expression in rainbow trout (Oncorhynchus mykiss) selected for high- and low-responsiveness to stress

The production and welfare of intensively reared fish would be improved by reducing stress responsiveness. One approach to achieving this goal is selective breeding utilising stress-responsive genes as direct genetic markers of the desirable trait. As a first step in this process, microarray analysis has been carried out on liver tissues of rainbow trout selectively bred for high (HR) or low (LR) responsiveness to a stressor. Microarray hybridizations provided gene expression profiles for pooled samples of fish confined for 6 h, 24 h and 168 h and for individual fish (168 h only). 161 genes were shown to be differentially regulated in HR and LR fish during confinement exposure and eight of these gene expression profiles were validated by quantitative PCR. Genes of particular interest included intelectin-2 precursor which showed greater than 100-fold higher expression in HR fish compared to LR fish irrespective of whether the fish were confined or not; interferon inducible transmembrane protein 3 which was differentially stress-induced between the two lines; and hepatic pro-opiomelanocortin B (POMC B) which was upregulated during stress in HR fish but downregulated in LR fish. All these offer potential as direct markers of low stress responsiveness in a marker-assisted selection scheme.

The effects of acute and chronic hypoxia on cortisol, glucose and lactate concentrations in different populations of three-spined stickleback

The response of individuals from three different populations of three-spined sticklebacks to acute and chronic periods of hypoxia (4.4 kPa DO, 2.2 mg l⁻¹) was tested using measures of whole-body cortisol, glucose and lactate. Although there was no evidence of a neuroendocrine stress response to acute hypoxia, fish from the population least likely to experience hypoxia in their native habitat had the largest response to low oxygen, with significant evidence of anaerobic glycolysis after 2 h of hypoxia. However, there was no measurable effect of a more prolonged period (7 days) of hypoxia on any of the fish in this study, suggesting that they acclimated to this low level of oxygen over time. Between-population differences in the analytes tested were observed in the control fish of the acute hypoxia trial, which had been in the laboratory for 16 days. These differences were not apparent among the control fish in the chronic exposure groups that had been held in the laboratory for 23 days, suggesting that these site-specific trends in physiological status were acclimatory. Overall, the results of this study suggest that local environmental conditions may shape sticklebacks' general physiological profile as well as influencing their response to hypoxia.

Indices of stress in three-spined sticklebacks Gasterosteus aculeatus in relation to extreme weather events and exposure to wastewater effluent

Whole-body concentrations of cortisol and glucose were measured in three-spined sticklebacks Gasterosteus aculeatus from two rivers (Rivers Ray and Ock) in southern England during a 30 month period in order to assess effects on the stress axis of (1) remediation of a wastewater treatment works (WWTW) effluent (River Ray) and (2) episodic changes in flow rate arising from periods of high rainfall (Rivers Ray and Ock). The postcapture concentrations of cortisol and glucose in fish from both rivers did not exhibit a seasonal periodicity but did show significant between-sample, between-site and between-river variation, superimposed upon a consistent downward trend for each analyte during the monitoring period. Corticosteroid and glucose concentrations following capture were inversely linked with a progressive increase in condition of the fish during this period. Site-dependent trends possibly related to exposure to the WWTW effluent were detected for both analytes in fish from the River Ray. For fish in the River Ray, a significant proportion of variation in both corticosteroid and glucose concentrations, additional to the downward trend with time, was accounted for by temporal proximity of the sample to exceptional flow events arising from episodes of high rainfall and high turbidity. This relationship was not statistically significant for fish from the River Ock. These data suggest that the responsiveness of the stress axis in free-living G. aculeatus may be altered by exposure to WWTW effluent and by exposure to physical changes in the aquatic environment such as those arising from extreme weather events. The magnitude of these effects may be increased by exposure to both stressors concurrently.

Effects of sewage effluent remediation on body size, somatic RNA: DNA ratio, and markers of chemical exposure in three-spined sticklebacks

Body mass, fork length, RNA:DNA ratio, specific growth rate, and hepatic EROD activity and CYP1A expression, were measured in three-spined sticklebacks in the River Ray (south west England) at sites downstream of an urban waste water treatment works (WWTW) prior to, and following, remediation of the effluent with granular activated carbon (GAC) tertiary treatment. During the same two-year period fish were also sampled from a neighbouring reference river (R. Ock). The WWTW effluent elevated water temperatures and nutrient content in the R. Ray and rendered a direct comparison of fish populations in the two rivers untenable. Instead, the stability of population parameters within each river during matched pre- and post-remediation periods was compared. Stickleback populations in both rivers were annual but fish in the R. Ray spawned earlier and were larger than those in the R. Ock. In the R. Ray fish gained mass throughout the winter months whereas in the R. Ock growth was much reduced during this period. In fish from the R. Ray the somatic RNA:DNA ratio remained elevated during May-November after remediation, rather than declining as in the same period pre-remediation and as was the case for fish in the R. Ock during both periods. The specific growth rate of the first post-remediation generation of sticklebacks in the R. Ray was higher than that of the previous pre-remediation generation. Following remediation there was no decline in hepatic EROD activity or in the abundance of hepatic CYP1A transcripts in fish in the R. Ray suggesting that the primary route of exposure to contaminants for these fish was not via the water column, and that the change in performance of the fish post-remediation was not impeded by continued exposure to contaminants. Both EROD activity and CYP1A expression increased in fish in the R. Ock during the later stages of the study suggesting that the fish in this river were exposed to an unidentified contaminant episode. This may have been linked with the poorer performance of fish in the R. Ock during the post-remediation period. The improved performance of fish in the R. Ray suggest that there may be factors in good quality secondary treated sewage effluent which can adversely influence the performance of fish populations, directly or indirectly, and which can be removed by tertiary treatment.

Physiological and genetic correlates of boldness: characterising the mechanisms of behavioural variation in rainbow trout, Oncorhynchus mykiss

Bold, risk-taking animals have previously been putatively linked with a proactive stress coping style whereas it is suggested shyer, risk-averse animals exhibit a reactive coping style. The aim of this study was to investigate whether differences in the expression of bold-type behaviour were evident within and between two lines of rainbow trout, Oncorhynchus mykiss, selectively bred for a low (LR) or high (HR) endocrine response to stress, and to link boldness and stress responsiveness with the expression of related candidate genes. Boldness was determined in individual fish over two trials by measuring the latency to approach a novel object. Differences in plasma cortisol concentrations and the expression of eight novel candidate genes previously identified as being linked with divergent behaviours or stress were determined. Bold and shy individuals, approaching the object within 180 s or not approaching within 300 s respectively, were evident within each line, and this was linked with activity levels in the HR line. Post-stress plasma cortisol concentrations were significantly greater in the HR line compared with the LR line, and six of the eight tested genes were upregulated in the brains of LR fish compared with HR fish. However, no direct relationship between boldness and either stress responsiveness or gene expression was found, although clear differences in stress physiology and, for the first time, gene expression could be identified between the lines. This lack of correlation between physiological and molecular responses and behavioural variation within both lines highlights the complexity of the behavioural-physiological complex.

A multivariate comparison of the stress response in three salmonid and three cyprinid species: evidence for inter-family differences

The response of six species of freshwater fishes, from the families Cyprinidae (common carp Cyprinus carpio, roach Rutilus rutilus and chub Leuciscus cephalus) and Salmonidae (rainbow trout Oncorhynchus mykiss, brown trout Salmo trutta and Arctic charr Salvelinus alpinus), to a standardized stressor was evaluated. A 6 h period of confinement resulted in changes to plasma cortisol, glucose, amino acid and lactate levels compared with unconfined controls. There were significant differences in the response profiles both within and between families. The cyprinid species exhibited higher and more sustained stress-induced increases in plasma cortisol and glucose than the salmonid species. In cyprinids, plasma lactate and plasma amino acid concentration showed less disturbance following stress than in salmonids. The results of the study, together with an evaluation of previously published data for eight salmonid species and six cyprinid species, support the hypothesis that differences in core elements of the stress response exist between species of fishes, and that this variation may have a systematic basis.

Melanin-based skin spots reflect stress responsiveness in salmonid fish

Within animal populations, genetic, epigenetic and environmental factors interact to shape individual neuroendocrine and behavioural profiles, conferring variable vulnerability to stress and disease. It remains debated how alternative behavioural syndromes and stress coping styles evolve and are maintained by natural selection. Here we show that individual variation in stress responsiveness is reflected in the visual appearance of two species of teleost fish; rainbow trout (Oncorhynchus mykiss) and Atlantic salmon (Salmo salar). Salmon and trout skin vary from nearly immaculate to densely spotted, with black spots formed by eumelanin-producing chromatophores. In rainbow trout, selection for divergent hypothalamus-pituitary-interrenal responsiveness has led to a change in dermal pigmentation patterns, with low cortisol-responsive fish being consistently more spotted. In an aquaculture population of Atlantic salmon individuals with more spots showed a reduced physiological and behavioural response to stress. Taken together, these data demonstrate a heritable behavioural-physiological and morphological trait correlation that may be specific to alternative coping styles. This observation may illuminate the evolution of contrasting coping styles and behavioural syndromes, as occurrence of phenotypes in different environments and their response to selective pressures can be precisely and easily recorded.

Acute phase gene expression in rainbow trout (Oncorhynchus mykiss) after exposure to a confinement stressor: A comparison of pooled and individual data

This study set out to investigate whether differential expression of genes for acute phase proteins in rainbow trout (Oncorhynchus mykiss) could be induced by confinement stress, a non-invasive method of activating the neuroendocrine stress response. In addition, a second objective was to assess the variation in gene expression between individual fish within the population of stressed fish in an attempt to identify APP genes having uniform and consistent changes in expression during stress. The liver was chosen for this investigation as it is the primary site of acute phase protein synthesis. Relative expression of the eight genes including transferrin, fibrinogen-like protein 2 (flp2), alpha-1-anti-proteinase-like protein (alpha1-antiprot), leukocyte cell-derived chemotaxin 2 (LECT2), pentraxin, serum amyloid A (SAA), haptoglobin (Hp), and differentially regulated trout protein 1 (DRTP1) was analysed by quantitative real-time PCR (qPCR) over 5 experimental time points spanning the course of a week. The results showed that the expression of three genes, SAA, haptoglobin and DRTP1, were most altered as a result of exposure to confinement stress. A correlation was identified between the expression of haptoglobin and DRTP1. Gene expression analyses in individual fish found that the transcript levels of haptoglobin and DRTP1 genes varied much less between individuals than was the case for SAA. The increase of haptoglobin and DRTP1 gene expression and its uniformity in response to stress make these genes potential biomarkers for stress in trout.

Detection of the anti-androgenic effect of endocrine disrupting environmental contaminants using in vivo and in vitro assays in the three-spined stickleback

We have previously developed a novel in vitro assay that utilises cultures of primed female stickleback kidney cells for the screening of potential androgenic and anti-androgenic environmental contaminants. Stickleback kidney cells are natural targets for steroid hormones and are able to produce a protein, spiggin, in response to androgenic stimulation. We undertook a combined in vivo/in vitro study where we used the magnitude of spiggin production as an endpoint to test the anti-androgenic properties of the pharmaceutical androgen antagonist flutamide and three environmental contaminants: the organophosphate insecticide fenitrothion, the urea-based herbicide linuron and the fungicide vinclozolin. In vitro, kidney cells were exposed to a range of concentrations [from 10(-14) M (2.5 pg/L) up to 10(-6) M (280 microg/L)] of the test compounds alone for determining agonist activities, or together with 10(-8) M (3 microg/L) dihydrotestosterone (DHT) for determining antagonist activities. An in vivo flow-through aquarium-based study was carried out in parallel. Female sticklebacks were exposed to a range of concentrations of the same chemicals alone or in combination with DHT (5 microg/L) for 21 days. All of the compounds significantly inhibited DHT-induced spiggin production in a concentration-dependent manner in both the in vitro (FN > or = FL > or = LN > VZ) and in vivo (FN > FL > or = VZ > LN) assays. Fenitrothion and flutamide inhibited spiggin production in vitro at a concentration as low as 10(-12) M (P < 0.05), while linuron and vinclozolin inhibited DHT-induced spiggin production at concentrations of 10(-10) M (P < 0.05) and 10(-6) M (P < 0.001) respectively. Similarly, fenitrothion and flutamide were the most potent chemicals in vivo and significantly reduced DHT-induced spiggin production at a concentration of 10 microg/L and 25 microg/L respectively (P < 0.01). Both linuron and vinclozolin induced a significant decrease in DHT-induced spiggin production at a concentration of 100 microg/L when tested in vivo. In addition, kidney cell primary culture was used to test the (anti-)androgenic effects of the major environmental contaminants: oestradiol (E2), nonylphenol (NP) and bisphenol A (BPA) for the first time in teleosts. We observed that these compounds were able to significantly inhibit spiggin production at high doses (E2: 270 microg/L; NP: 2.2 microg/L; BPA: 2.3 microg/L). When tested in the absence of DHT, none of the compounds showed a significant agonistic activity in either in vivo or in vitro assays. Overall, our data further demonstrate that kidney cell primary culture is a reliable and a sensitive screening tool for the detection of (anti-)androgenic compounds. In addition, our study represents the first attempt to develop a combined in vivo/in vitro screening strategy for assessing the effects of (anti-)androgenic endocrine disrupters.

Do suspended sediments modulate the effects of octylphenol on rainbow trout?

A system was devised which allows particles to remain in suspension in a conventional 60 L aquarium without undue disturbance to resident fish. Using this system, juvenile rainbow trout were exposed for one week to 4-tert-octylphenol (OP, 10-1000 microg/L) with or without the presence of suspended sediments (10-20mg/L of natural suspended sediments from the River Calder, UK). About 8% of the added OP partitioned to the solid phase. Vitellogenin levels were determined in the plasma of the exposed rainbow trout and showed a dose-dependent increase with regards to OP exposure concentration. Considerable variation in the vitellogenin response was observed between separate runs with the same OP concentration. There was no statistically significant (at P < 0.05) difference in plasma VTG levels between the OP treatments with or without suspended sediments. This suggests that the dissolved concentration is the key factor and natural suspended sediment neither protects against, nor exacerbates, the endocrine disrupting effect of OP on fish.

Intercalibration exercise using a stickleback endocrine disrupter screening assay

The Organisation for Economic Cooperation and Development (OECD) is currently validating a short-term fish screening protocol for endocrine disrupters (estrogens, androgens, and their antagonists and aromatase inhibitors), using three core species: fathead minnow, Japanese medaka, and zebrafish. The main endpoints proposed for the first phase of validation of the screen are vitellogenin (VTG) concentration, gross morphology (secondary sexual characteristics and gonado-somatic index), and gonadal histopathology. A similar protocol is concurrently being developed in the United Kingdom using the three-spined stickleback, with identical endpoints to those for the core species and, in addition, a unique androgen-specific endpoint in the form of spiggin (glue protein) induction. To assess the suitability of this species for inclusion in the OECD protocol alongside the core species, an intercalibration was conducted using 17beta-estradiol (a natural estrogen) and trenbolone (a synthetic androgen), thus mimicking a previous intercalibration with the core species. All three participating laboratories detected statistically significant increases in VTG in males after 14 d exposure to nominal concentrations of 100 ng/L 17beta-estradiol and statistically significant increases in spiggin in females after 14 d exposure to nominal concentrations of 5,000 ng/L trenbolone. The stickleback screen is reliable, possessing both relevant and reproducible endpoints for the detection of potent estrogens and androgens. Further work is underway to assess the relevance and suitability of the screen for weakly acting estrogens, anti-androgens, and aromatase inhibitors.

Chronic social stress in rainbow trout: does it promote physiological habituation?

The effect of chronic social stress on growth, energetic substrates and hormones was tested in rainbow trout, Oncorhynchus mykiss. After a 14-day isolation period, the fish were paired for 8 days. In order to expose fish to chronic intermittent social contact during pairing, they were maintained in direct contact with each other during the first day. After that, a black plastic screen partition was introduced in each tank, preventing direct contact between animals. Every day the partition was removed for 30 min, allowing physical interaction between fish. At the end of pairing period, they were isolated again for 13 days. Fish were weighed and blood was sampled frequently during the experiment. Plasma levels of cortisol, growth hormone, glucose, total protein and free amino acids were quantified. Both dominants and subordinates had specific growth rate decreased during the pairing period, but only subordinates increased when the stressor was abolished (dominants: 0.32+/-0.21 and 0.24+/-0.41, subordinates: -0.77+/-0.29 and 0.37+/-0.31, respectively). Dominants showed a higher cortisol level one week after pairing condition had been abolished than subordinates (dominants: 56.76+/-13.26, subordinates: 31.89+/-13.36). We conclude that chronic condition of intermittent social stress represents a stressful condition for animals of both hierarchical ranks and a treatment of one daily short direct contact between conspecifics does not promote habituation in fish, as mentioned for other stressors.

Impaired Reproduction in Three-Spined Sticklebacks Exposed to Ethinyl Estradiol as Juveniles1

To investigate the population-level effects of exposure to environmental endocrine disrupters, a mesocosm-scale study was carried out in which the reproductive performance of groups of free-spawning three-spined sticklebacks, Gasterosteus aculeatus, exposed as juveniles to a model estrogen, was assessed. Juvenile sticklebacks were exposed to ethinyl estradiol (EE(2)) at measured concentrations of (mean +/- SEM) 1.75 +/- 0.37 ng L(-1) and 27.7 +/- 1.08 ng L(-1) for 4 wk posthatch and then reared thereafter in pristine lake water until they reached adulthood. Exposure to the higher EE(2) concentration resulted in the occurrence of ovotestis among males, whereas no gonadal abnormalities were evident among males exposed to the lower concentration of EE(2). In addition, when spawning was allowed in the mesocosm environment, fewer nests were built per male, and fewer eggs were deposited per nest, in the group exposed to 27.7 ng L(-1). Males from this group also exhibited a less intense nuptial coloration than control males. In the group exposed to 1.75 ng L(-1) EE(2) posthatch, significantly fewer nests were built than in the control group. These results demonstrate that the timing of exposure to estrogenic contaminants, in developmental terms, is critically important. Short-term exposure to estrogens as juveniles can clearly influence reproductive performance as adults, despite all growth and development subsequent to the exposure period taking place in an estrogen-free environment. In addition, these results suggest that reproductive dysfunction can occur even in fish with no gross abnormalities in gonadal structure. This suggests that the absence of gonadal intersex is not a reliable indicator of the reproductive potential, or estrogen-exposure history, of fish populations or the only important factor involved in compromising the reproduction of estrogen-exposed fish.

A cDNA microarray assessment of gene expression in the liver of rainbow trout (Oncorhynchus mykiss) in response to a handling and confinement stressor

A purpose-designed microarray platform (Stressgenes, Phase 1) was utilised to investigate the changes in gene expression within the liver of rainbow trout during exposure to a prolonged period of confinement. Tissue and blood samples were collected from trout at intervals up to 648 h after transfer to a standardised confinement stressor, together with matched samples from undisturbed control fish. Plasma ACTH, cortisol, glucose and lactate were analysed to confirm that the neuroendocrine response to confinement was consistent with previous findings and to provide a phenotypic context to assist interpretation of gene expression data. Liver samples for suppression subtractive hybridisation (SSH) library construction were selected from within the experimental groups comprising "early" stress (2-48 h) and "late" stress (96-504 h). In order to reduce redundancy within the four SSH libraries and yield a higher number of unique clones an additional subtraction was carried out. After printing of the arrays a series of 55 hybridisations were executed to cover 6 time points. At 2 h, 6 h, 24 h, 168 h and 504 h 5 individual confined fish and 5 individual control fish were used with control fish only at 0 h. A preliminary list of 314 clones considered differentially regulated over the complete time course was generated by a combination of data analysis approaches and the most significant gene expression changes were found to occur during the 24 h to 168 h time period with a general approach to control levels by 504 h. Few changes in expression were apparent over the first 6 h. The list of genes whose expression was significantly altered comprised predominantly genes belonging to the biological process category (response to stimulus) and one cellular component category (extracellular region) and were dominated by so-called acute phase proteins. Analysis of the gene expression profile in liver tissue during confinement revealed a number of significant clusters. The major patterns comprised genes that were up-regulated at 24 h and beyond, the primary examples being haptoglobin, beta-fibrinogen and EST10729. Two representative genes from each of the six k-means clusters were validated by qPCR. Correlations between microarray and qPCR expression patterns were significant for most of the genes tested. qPCR analysis revealed that haptoglobin expression was up-regulated approximately 8-fold at 24 h and over 13-fold by 168 h.

Variable neuroendocrine responses to ecologically-relevant challenges in sticklebacks

Variable neuroendocrine responses to ecologically-relevant challenges in sticklebacks. PHYSIOL BEHAV 00(0) 000-000, 2006. Here, we compare the behavioral, endocrine and neuroendocrine responses of individual sticklebacks exposed to either an unfamiliar conspecific or to a predator. We found that the two stressors elicited a similar hypothalamic-pituitary-interrenal response as assessed by whole-body concentrations of cortisol, but produced quite different patterns of change in brain monoamine and monoamine metabolite content as assessed by concentrations of serotonin (5-HT), dopamine (DA), norepinephrine (NE) and the monoamine metabolites 5-hydroxyindole acetic acid (5-HIAA), homovanillic acid (HVA) and 3-4-dihydroxyphenylacetic acid (DOPAC). For example, relative to baseline levels, NE levels were elevated in individuals exposed to a predator but were lower in individuals confronted by a challenging conspecific. Levels of monoamine neurotransmitters in specific regions of the brain showed extremely close links with behavioral characteristics. Frequency of attacking a conspecific and inspecting a predator were both positively correlated with concentrations of NE. However, whereas serotonin was negatively correlated with frequency of attacking a conspecific, it was positively associated with predator inspection. The data indicate that the qualitative and quantitative nature of the neuroendocrine stress response of sticklebacks varies according to the nature of the stressor, and that interindividual variation in behavioural responses to challenge are reflected by neuroendocrine differences.

Evolutionary background for stress-coping styles: relationships between physiological, behavioral, and cognitive traits in non-mammalian vertebrates

Reactions to stress vary between individuals, and physiological and behavioral responses tend to be associated in distinct suites of correlated traits, often termed stress-coping styles. In mammals, individuals exhibiting divergent stress-coping styles also appear to exhibit intrinsic differences in cognitive processing. A connection between physiology, behavior, and cognition was also recently demonstrated in strains of rainbow trout (Oncorhynchus mykiss) selected for consistently high or low cortisol responses to stress. The low-responsive (LR) strain display longer retention of a conditioned response, and tend to show proactive behaviors such as enhanced aggression, social dominance, and rapid resumption of feed intake after stress. Differences in brain monoamine neurochemistry have also been reported in these lines. In comparative studies, experiments with the lizard Anolis carolinensis reveal connections between monoaminergic activity in limbic structures, proactive behavior in novel environments, and the establishment of social status via agonistic behavior. Together these observations suggest that within-species diversity of physiological, behavioral and cognitive correlates of stress responsiveness is maintained by natural selection throughout the vertebrate sub-phylum.

The effect of elevated blood cortisol levels on the extinction of a conditioned stress response in rainbow trout

Following previously published observations that a conditioned response (CR) was lost more quickly by rainbow trout (Oncorhynchus mykiss) exhibiting a high responsiveness to stressors than by low responding individuals this study was designed to investigate the effects of exogenous cortisol on the retention of a CR in unselected rainbow trout. Fish held in isolation were conditioned over a 10-day period by pairing an innocuous signal (conditioned stimulus, CS: a water jet played on the surface of the tank water) with a mild stressor (unconditioned stimulus, US: 30 min of confinement). This resulted in a brief elevation of plasma cortisol levels (the CR) when the fish was exposed to the CS only. The effect of exogenous cortisol on the retention of the CR was evaluated by comparing the performance of fish that received cortisol-containing slow-release intraperitoneal implants, with fish receiving vehicle-only implants. Retention of the CR was assessed at intervals up to 35 days after conditioning ceased. The CR was considered to be evident when 30 min following presentation of the CS, mean plasma cortisol levels were significantly higher in conditioned than untrained fish. On day 1 both cortisol-implanted and vehicle-implanted conditioned fish exhibited a CR. However, from day 5 onwards the CR was observed only in the vehicle-implanted and conditioned group. This finding indicates that administration of cortisol accelerated the extinction of the CR in the cortisol-implanted fish, suggesting that elevated plasma cortisol levels can impair memory processes in rainbow trout.

Contamination of headwater streams in the United Kingdom by oestrogenic hormones from livestock farms

Most studies of hormonal activity in rivers have focused on inputs from sewage treatment works (STW), and their consequences for endocrine disruption in fish. It is possible that livestock is contributing to this hormonal activity in rivers. This study represents a search for evidence of steroid hormone contamination in streams associated with livestock farms. The majority of the 10 sites selected were streams running through dairy farms, although some examples of beef, sheep and pigs were included. Passive water samplers (Polar Organic Chemical Integrative Samplers-POCIS) were deployed up- (control) and down-stream of the farms for 3 to 10 weeks (mean=39 days) during the period November 2004 to January 2005. At one site, water samples were also taken automatically during rainfall events. All samples were solvent-extracted. Total oestrogenic activity in concentrates of the extracts was analysed using the Yeast Estrogen Screen (YES) calibrated against 17beta-oestradiol (E2), while oestrone (E1), E2 and 17alpha-ethinylestradiol (EE2) were analysed by liquid chromatography-mass spectrometry (LC-MS/MS). Stream water from the entirety of only one rainfall event was sampled directly, but this revealed background activity (E2 equivalents) of 0-0.3 ng/l, rising to a transient peak of 9.4 ng/l. Average oestrogenic activity at this site as estimated from the POCIS samplers was 1.8-2.7 ng E2 equiv./l. Estimated average oestrogenic activity across all sites (with one exception) lay in the range 0-26.5 ng E2 equiv./l (mean=2.0 ng/l; S.D.=5.1), based on the POCIS samples. The outlier was 292 ng/l, and this could not be specifically linked with livestock rearing. 92% of monitoring stations (at least one on each farm) contained some oestrogenic activity, and activity was higher at downstream sites in 50% of cases. Although no EE2 was detected analytically in any stream, E1 and E2 were almost ubiquitous, with E2 equivalents ranging from 0.04 to 3.6 ng/l across all sites. Furthermore, steroid concentrations downstream of livestock were higher than upstream in 60% of cases, more markedly so than for the YES data. In several cases, activity upstream was greater than downstream, and this tended to be associated with higher activity than could be accounted for by the hormone analyses. Both the YES and chemical analytical data suggest that fish in headwater streams on or near some livestock farms may be at risk of endocrine disruption.

Serotonergic characteristics of rainbow trout divergent in stress responsiveness

Juvenile rainbow trout divergent in their cortisol response to confinement stress (HR: high responsive or LR: low responsive fish) were exposed to either 1 or 3 h of confinement stress. Untreated fish served as control. After the exposure blood and brain samples were collected. From the blood samples, the levels of cortisol and catecholamines were determined, while the brain serotonergic and monoamineoxidase (MAO) activity was determined in four different brain areas (brain stem, hypothalamus, telencephalon and optic tectum). Our results show that the LR fish responds to handling stress with a higher increase in plasma epinephrine compared to HR fish. Our results also show that confinement stress leads to a larger increase in the serotonergic activity in the brain stem and telencephalon in LR fish compared to HR fish. These results support the hypothesis that stress coping strategies similar to those described in mammals also exists in fish. Further, our results have shown that the MAO activity increases in optic tectum and hypothalamus of rainbow trout during confinement stress, while it remains unchanged or decreases in brain stem and telencephalon. Moreover, the MAO activity does not differ between the two selection lines. This indicates that MAO participates actively in the stress response without contributing to the differences in stress coping strategies.

Divergence in behavioural responses to stress in two strains of rainbow trout (Oncorhynchus mykiss) with contrasting stress responsiveness

The aim of this study was to establish whether two lines of rainbow trout divergent for their plasma cortisol response to a standardized stressor would show consistent differences in their behavioural response to a range of challenging situations. Our results show that the high- and low-responding (HR and LR) lines of rainbow trout did not differ in the aggression shown towards an intruder or in their response to the introduction of a novel object to their home environment. However, there was a difference in behaviour between the two selection lines when they were exposed to two unfamiliar environments. These results suggest that the behaviour of the HR and LR fish differs when they are challenged in unfamiliar environments, while their behaviour does not differ when they are challenged in their home environment. These observations are in agreement with studies on mammals that show that individuals with reactive coping styles perform similarly to proactive animals when they are challenged in a familiar environment, while they show different behaviour when they are challenged in unfamiliar environments. Thus, these results provide further evidence that the HR and LR selection lines of rainbow trout exemplify the two different coping styles described in mammals.

Overwinter fasting and re-feeding in rainbow trout: plasma growth hormone and cortisol levels in relation to energy mobilisation

This study investigated the roles of cortisol and growth hormone (GH) during a period of fasting in overwintering salmonid fish. Indices of carbohydrate (plasma glucose, liver glycogen), lipid (plasma free fatty acids (FFAs)) and protein metabolism (plasma protein, total plasma amino acids) were determined, together with plasma GH, cortisol and somatolactin (SL) levels at intervals in three groups of rainbow trout (continuously fed; fasted for 9 weeks then fed; fasted for 17 weeks). In fasted fish, a decline in body weight and condition factor was accompanied by reduced plasma glucose and hepatic glycogen and increased plasma FFA. No consistent elevation of plasma GH occurred until after 8 weeks of fasting when plasma GH levels increased ninefold. No changes were observed in plasma total protein and AA until between weeks 13 and 17 when both were reduced significantly. When previously fasted fish resumed feeding, plasma glucose and FFA, and hepatic glycogen levels rapidly returned to control values and weight gain resumed. No significant changes in plasma cortisol levels, related to feeding regime, were evident at any point during the study and there was no evidence that SL played an active role in the response to fasting. The results suggest that overwinter fasting may not represent a significant nutritional stressor to rainbow trout and that energy mobilisation during fasting may be achieved without the involvement of GH, cortisol or SL.

Extinction of a conditioned response in rainbow trout selected for high or low responsiveness to stress

Two lines of rainbow trout (Oncorhynchus mykiss) that exhibit divergent endocrine responsiveness to stressors also display disparate behavioral traits. To investigate whether the high-responding (HR) and low-responding (LR) fish also differ in cognitive function, the rate of extinction of a conditioned response was compared between the two lines. Groups of HR and LR fish were exposed to a paired conditioned stimulus (CS; water off) and unconditioned stimulus (US; confinement stressor). After exposure to 18 CS-US pairings, at least 70% of individuals of both lines acquired a conditioned response (CR) manifested as an elevation of blood cortisol levels on presentation of the CS only. Post-conditioning, the fish were tested by presentation of the CS at weekly intervals, for 4 weeks, with no further reinforcement, and the extinction of the CR in the two lines was compared. The decline in mean plasma cortisol levels after exposure to the CS over successive tests suggested that the CR was retained for a shorter period among the HR (<14 days) than LR fish (<21 days). The frequency of individuals within each line whose plasma cortisol levels indicated a stress response when exposed to the CS was significantly greater among the LR than HR fish at 14 and 21 days with no HR fish falling into this category at 21 days. At 28 days post-conditioning, there were no HR fish and only three LR fish were categorized as "stressed". These results suggest that there are differences in cognitive function between the two lines. Possible mechanisms underlying these differences are discussed.

Seasonality of the red blood cell stress response in rainbow trout (Oncorhynchus mykiss)

The beta-adrenergic stress response in red blood cells (RBCs) of rainbow trout shows seasonal changes in expression. We have explored the mechanisms underpinning this response by following, over a period of 27 months, changes in beta-adrenergic receptor (beta-AR) binding characteristics, beta-adrenergically stimulated RBC Na(+)/H(+) exchanger (betaNHE) activity, together with beta-AR and betaNHE mRNA levels and plasma steroid hormone and lactate levels. These parameters were measured at approximately monthly intervals in a single population of fish held under semi-natural conditions. Membrane-bound, high-affinity beta-ARs were present in RBCs at all sampling times, varying from 668+/-112 receptors cell(-1) to 2654+/-882 receptors cell(-1) (mean +/- S.E.M.; N=8). betaNHE activity, however, was reduced by 57% and 34% in December 1999 and February 2001, respectively, compared with an otherwise sustained influx that averaged 110.4+/-2.3 mmol l(-1) RBCs h(-1) (N=119). Only one reduction coincided with a spawning period but both were preceded by transient increases in circulating testosterone. betaNHE activity measured under standard conditions was not correlated with the number or affinity of beta-ARs nor with water temperature, but both beta-AR numbers and betaNHE activity were positively related to their respective mRNA levels (P=0.005 and 0.038, respectively). Pharmaceutical intervention in the transduction cascade linking the beta-AR and betaNHE failed to indicate any failure of the transduction elements in RBCs displaying low betaNHE activity. Similarly, we failed to demonstrate any link between seasonal cortisol fluctuations and seasonally reduced betaNHE activity. However, the betaNHE activity of age-separated RBC fractions showed that younger RBCs had a significantly higher betaNHE response than older RBCs, consistent with the seasonal reductions in betaNHE being linked to turnover of RBCs and erythropoiesis. Testosterone is known to induce erythropoiesis and we conclude that seasonal reductions in betaNHE are not caused by changes in beta-AR numbers but may be linked to testosterone-induced erythropoiesis.

Behavioral and neuroendocrine correlates of displaced aggression in trout

In humans and other primates, violent actions performed by victims of aggression are often directed toward an individual or object that is not the source of provocation. This psychological phenomenon is often called displaced aggression. We demonstrate that displaced aggression is either rooted in evolutionarily conserved behavioral and neuroendocrine mechanisms, or represent a convergent pattern that has arisen independently in fish and mammals. Rainbow trout that briefly encountered large, aggressive fish reacted with increased aggression toward smaller individuals. There was a strong negative correlation between received aggression and behavioral change: Individuals subjected to intense aggression were subdued, while moderate assaults induced strong agitation. Patterns of forebrain serotonin turnover and plasma cortisol suggest that the presence of socially subordinate fish had an inhibitory effect on neuroendocrine stress responses. Thus, subordinate individuals may serve as stress-reducing means of aggressive outlet, and displaced aggression toward such individuals appears to be a behavioral stress coping strategy in fishes.

Time-course of the effect of dietary L-tryptophan on plasma cortisol levels in rainbow trout Oncorhynchus mykiss

Isolated juvenile rainbow trout were fed a feed supplemented with L-tryptophan (TRP) for 3, 7 or 28 days, after which they were either sampled directly (undisturbed) or subjected to a standardised stressor prior to sampling. Controls (stressed and undisturbed) received the same feed but without any supplementary TRP. Stress resulted in a significant elevation of plasma [cortisol] in fish fed control feed and in fish fed TRP-supplemented feed for 3 and 28 days. However, fish fed TRP-supplemented feed for 7 days did not show any significant elevation of plasma [cortisol] in response to stress. Plasma levels of adrenocorticotropin followed the same general pattern as cortisol. Plasma and brain [TRP] were elevated in fish fed TRP-supplemented feed. The amino acid TRP is the precursor of the monoamine neurotransmitter serotonin (5-hydroxytryptamine, 5-HT) and the brain 5-HT system is known to be involved in the control of the hypothalamic-pituitary-interrenal (HPI) axis. Fish fed TRP-supplemented feed showed elevated levels of 5-hydroxyindoleacetic acid (5-HIAA, a major 5-HT metabolite) in the hypothalamus and optic tectum. However, TRP treatment did not appear to result in any effects on brain dopaminergic activity and the effects on brain norepinephric activity do not support a role of norepinephrine in mediating the effects of TRP on HPI axis reactivity in rainbow trout.

Divergence of endocrine and metabolic responses to stress in two rainbow trout lines selected for differing cortisol responsiveness to stress

Rainbow trout (Oncorhynchus mykiss) of two lines selected for low (LR) and high (HR) cortisol stress-responsiveness were subjected to confinement for a period of 336 h. Endocrine (plasma cortisol, hepatic cortisol binding) and metabolic (plasma glucose, lactate, amino acids; hepatic glycogen and alanine aminotransferase levels) indices of stress were measured at intervals in confined and unconfined fish of both lines. During confinement plasma cortisol concentration reached maximum values earlier in HR fish (2h) than in LR fish (6h) returning to control values within 336 h in both lines. Paradoxically, although both HR and LR lines displayed a characteristic metabolic stress response, these changes were more pronounced in LR fish. Plasma glucose and lactate levels increased during confinement in both lines but to a significantly greater extent in LR fish. Confinement significantly elevated plasma amino acids to a greater extent in LR fish than in HR fish. Liver glycogen concentration was depleted most rapidly in LR fish but was significantly higher in confined fish of both lines than controls at the end of the experiment. No significant changes were observed in hepatic alanine aminotransferase activity during confinement. Confined fish of both lines displayed a decrease in hepatic cortisol receptor abundance within 24h and this was more sustained in HR fish. The more pronounced disturbance of a broad range of indicators of stress in confined LR fish, compared to HR fish, throws doubt on the magnitude of the cortisol response being the primary driver of these differences.

Recombinant interleukin-1 beta activates the hypothalamic-pituitary-interrenal axis in rainbow trout, Oncorhynchus mykiss

The present study provides the first direct evidence that implicates fish cytokines as the effector molecules by which the immune system signals the neuroendocrine system and activates the hypothalamic-pituitary-interrenal stress axis. I.p. injections of trout recombinant interleukin-1 beta (rIL-1 beta) or E. coli lipopolysaccharide (LPS), at concentrations known to induce immune/inflammatory responses in vivo (0.1-0.6 nmol/kg and 1.3 mg/kg respectively), significantly elevated plasma cortisol levels in a dose- and/or time-dependent manner. However, in contrast to general stress responses in fish, under the conditions employed in this study, no specific treatment effects on plasma glucose levels could be demonstrated. The trout IL-1 beta peptides (P1 and P3), which are homologous to receptor-binding sequences of human IL-1 beta, failed to influence the prevailing cortisol concentration even though an equivalent dose has been found to have immunostimulatory properties in vivo. Blockade of endogenous ACTH release by administration of the synthetic glucocorticoid dexamethasone prevented the rIL-1 beta/LPS-mediated elevation of plasma cortisol, suggesting that IL-1 beta and LPS modulate cortisol secretion via effects at the level of the hypothalamic-pituitary axis. These data indicate that, with respect to IL-1 beta, cytokine signalling between the immune and neuroendocrine systems in mammals appears to be conserved in lower vertebrates.

Differences in behaviour between rainbow trout selected for high- and low-stress responsiveness

Two F1 lines of rainbow trout Oncorhynchus mykiss, divergent for plasma cortisol responsiveness, were generated by individual selection for post-stress cortisol values within the F0 generation. Adult females of the F1 generation were transferred to rearing in social isolation in observation tanks. After 6 days, locomotor activity in high-responding (HR) and low-responding (LR) individuals was quantified as time spent moving during a 20 min observation period. Behavioural observations were repeated the next day with a smaller conspecific intruder present in each observation tank. Differential hypothalamus–pituitary–interrenal axis activity in the two lines was subsequently confirmed by a standardised confinement stress test, which resulted in significantly higher plasma cortisol concentrations in HR than LR fish. HR fish displayed higher levels of locomotor activity than LR fish in the presence of an intruder, but not when in isolation. Aggressive behaviour towards the intruder was not seen, suggesting either a state-dependent lack of territorial aggression, or chronic stress in the experimental fish. A significantly higher incidence of feed intake was seen in LR trout when held in observation tanks (40 % versus 0 % of the fish took food when in isolation), suggesting that these fish acclimated more successfully to the experimental conditions than HR fish did. These results suggest that selection for stress responsiveness in salmonid fish leads to behavioural alterations, which are of potential importance to the performance of these fish in aquaculture rearing operations.

Stress responsiveness affects dominant-subordinate relationships in rainbow trout

The magnitude by which plasma cortisol levels increase following exposure to a stressor is a heritable trait in rainbow trout. The relative growth in coculture of F1 lines selected for high responsiveness (HR) and low responsiveness (LR) to a confinement stressor suggested that behavioral characteristics related to food acquisition, aggression, or competitive ability might differ between the two lines. This hypothesis was tested using the F2 generation of the selected lines. The F2 lines clearly exhibited the characteristics of the F1 parents, displaying significantly divergent plasma cortisol responses to a 1-h confinement stressor and a high heritability for the trait. Behavioral differences between the lines were assessed by observing the outcome of staged fights for dominance in size-matched pairs of HR and LR fish. The identification of dominant and subordinate fish within each pair on the basis of their behavior was supported by the levels of blood cortisol in the fish attributed to each group (dominant << subordinate). Fish from the LR line were identified as dominant in significantly more trials than were HR individuals. The results suggest that behavioral attributes that affect the outcome of rank-order fights are closely linked to the magnitude of the plasma cortisol response to stress in rainbow trout. Whether the link is causal or circumstantial is not yet evident.

Nonylphenol affects gonadotropin levels in the pituitary gland and plasma of female rainbow trout

Female rainbow trout (Oncorhynchus mykiss) were exposed to 4-nonylphenol (NP) at (mean measured) concentrations of 0.7, 8.3, and 85.6 micrograms/L for 18 weeks, during early ovarian development. Fish were sampled sublethally every six weeks, and terminal samples were taken at 18 weeks. NP induced an estrogenic effect (the synthesis of vitellogenin) at concentrations of 8.3 and 85.6 micrograms/L. An effect on gonadotropin synthesis and secretion was also observed. Plasma follicle stimulating hormone (FSH) levels and FSH gene expression in the pituitary were the most sensitive endpoints assessed, being reduced at the lowest dose employed (0.7 microgram NP/L). Pituitary gland luteinizing hormone (LH) content was significantly lower in fish exposed to 85.6 micrograms NP/L, and LH gene expression was suppressed in fish exposed to 8.3 and 85.6 micrograms NP/L. In contrast, plasma LH concentration increased in these fish, but by a very minor absolute amount, and returned to control levels by the final sampling time. Gonadal development ceased in the fish exposed to 85.6 micrograms NP/L, and steroidogenesis in these fish was also markedly inhibited. Although the mechanisms underlying these responses are unknown, this study demonstrates that NP has adverse effects on pituitary function that can result in inhibition of ovarian development.

ACTH does not mediate divergent stress responsiveness in rainbow trout

Two lines of rainbow trout selected for high (HR) and low (LR) responsiveness to a standardised confinement stressor displayed a sustained divergence in plasma cortisol levels during a 3-h period of confinement (max.: HR: 167+/-13 ng ml(-1); LR: 103+/-8 ng ml(-1); P<0.001). However, no significant difference in plasma ACTH levels was evident (max: HR: 153+/-9 pg ml(-1); LR: 142+/-7 pg ml(-1)). Dexamethasone (DEX) was administered to HR and LR fish to block endogenous adrenocorticotropin (ACTH) release. Administration of a weight-adjusted dose of ACTH to the DEX-blocked fish elevated plasma cortisol levels to a significantly greater extent in HR (233+/-24 ng ml(-1)) than LR (122+/-14 ng ml(-1)) fish (P<0.001). Plasma cortisol levels in DEX-blocked HR and LR fish after sham injection were low but also significantly different (HR: 6.7+/-1 ng ml(-1); LR: 2.2+/-0.2 ng ml(-1); P<0.001). These results indicate that modulation of cortisol responsiveness to stressors in HR and LR fish resides, at least in part, downstream of the hypothalamic-pituitary axis.

Brain monoaminergic activity in rainbow trout selected for high and low stress responsiveness

This paper investigates whether two lines of rainbow trout displaying genetically determined variation in stress responsiveness and behavior also show differences in brain monoaminergic activity. In several brain regions, strains of rainbow trout selected for consistently high or low post-stress cortisol levels displayed differences in tissue concentrations of monoamines and/or monoamine metabolites, or in metabolite/monoamine ratios. High-responsive trout reacted to stress by an increase in the concentrations of both serotonin (brain stem), dopamine (brain stem), and norepinephrine (optic tectum, telencephalon), whereas low-responsive fish did not. Brain stem and optic tectum concentrations of monoamine metabolites were also elevated after stress in high responders, but not in low-responsive fish. The simultaneous increase in the concentration of monoamines and their metabolites suggests that both synthesis and metabolism of these transmitters were elevated after stress in high-responsive trout. A divergent pattern was seen in the hypothalamus, where low-responsive fish displayed elevated levels of 5-hydroxyindoleacetic acid (a serotonin metabolite) and 3-methoxy-4-hydroxyphenylglycol (a norepinephrine metabolite). In the telencephalon, both populations had elevated concentrations of these metabolites after stress. These results clearly suggest that selection for stress responsiveness in rainbow trout is also associated with changes in the function of brain monoaminergic systems. The possible functional significance of these observations is discussed with respect to the physiological and behavioral profile of these strains of fish. Literature is reviewed showing that several factors affecting brain monoaminergic activity might be altered by selection for stress responsiveness, or alternatively be under direct influence of circulating glucocorticoids.

High blood cortisol levels and low cortisol receptor affinity: is the chub, Leuciscus cephalus, a cortisol-resistant teleost?

In contrast to the relatively minor intra- and interspecies differences in blood cortisol levels reported for salmonid species, there is a more pronounced distinction between cortisol levels among the Salmonidae and the Cyprinidae, with both basal and stress-induced cortisol levels markedly higher in the latter. This study shows that in the chub, Leuciscus cephalus, a widely distributed European cyprinid, mean blood cortisol levels during stress (1500 ng mL(-1)) exceeded those reported for most other species of fish and, even in unstressed chub, cortisol levels (50-100 ng mL(-1)) were within the range known to cause immunosuppression, growth retardation, and reproductive dysfunction in salmonid fish. The chub appears to be atypical only with respect to plasma cortisol levels; the levels of plasma glucose and plasma lactate in unstressed and stressed chub are similar to those reported for other species. Plasma levels of 11-ketotestosterone in males and 17beta-estradiol in females are lower than those reported for salmonids but similar to those reported for other cyprinid species and display clear stress-induced reduction. Comparative analysis of the binding characteristics of the trout and chub gill cortisol receptor revealed that the total number of binding sites in gill tissue for each species was similar (B(max); approximately 50-100 fmol mg(-1) protein). However, the affinity of the binding site for cortisol displayed an eightfold difference between the species (rainbow trout: K(d) approximately 6 nM; chub: K(d) approximately 50 nM). Therefore, the potentially adverse effects of high circulating levels of cortisol found both at rest and under conditions of stress in chub may be offset by the lower affinity of the cortisol receptor, rather than the abundance of target-tissue receptor sites. This strategy is similar to that reported for some glucocorticoid-resistant rodents and New World primates.

Modification of the plasma cortisol response to stress in rainbow trout by selective breeding

Male and female rainbow trout were segregated into high- and low-responding individuals (HR, LR) on the basis of their plasma cortisol response to a 3-h period of confinement imposed at monthly intervals for 5 months. Consistent divergence was obtained in the responsiveness of the two groups, although the difference between LR and HR groups was greater in female fish (56 c.f. 116 ng ml(-1)) than in males (45 c.f. 69 ng ml(-1)). Progeny groups (full-sib families) were obtained from the pairing of HR males and females and LR males and females. A third progeny group (US) was obtained by random pairing of parents which were not selected as HR or LR. Poststress plasma cortisol levels in the progeny were first tested at 6 months after hatch and were significantly correlated with the response of the corresponding parental groups, HR > US > LR (178, 126, 81 ng ml(-1), respectively). The difference in responsiveness between LR and HR groups was demonstrated in all four subsequent tests over a 12-month period. There were no significant differences in baseline plasma cortisol levels in LR and HR groups prior to confinement. During a 4-h period of confinement, the differences in plasma cortisol levels between LR and HR fish were sustained throughout, indicating that the trait upon which the fish were selected was related to absolute maximum levels of circulating cortisol and not to the rate of change of cortisol levels during exposure to a stressor. A moderately high heritability (h(2)) for confinement-induced plasma cortisol of 0.41 was obtained by a parent-progeny regression. Manipulation of stress responsiveness in fish by selective breeding offers scope for optimizing performance under intensive rearing conditions but also provides a useful research tool for investigating the operation of the endocrine stress response.