As climate change-induced heatwaves become more common, phenotypic plasticity at multiple levels is a key mitigation strategy by which organisms can optimise selective outcomes. In ectotherms, ...changes to both metabolism and behaviour can help alleviate thermal stress. Nonetheless, no study in any ectotherm has yet empirically investigated how changing temperatures affect among-individual differences in the associations between these traits. Using the beadlet anemone (Actinia equina), an intertidal species from a thermally heterogeneous environment, we investigated how individual metabolic rates, linked to morphotypic differences in A. equina, and boldness were related across changing temperatures. A crossed-over design and a temporal control were used to test the same individuals at a non-stressful temperature, 13°C, and under a simulated heatwave at 21°C. At each temperature, short-term repeated measurements of routine metabolic rate (RMR) and a single measurement of a repeatable boldness-related behaviour, immersion response time (IRT), were made. Individual differences, but not morphotypic differences, were highly predictive of metabolic plasticity, and the plasticity of RMR was associated with IRT. At 13°C, shy animals had the highest metabolic rates, while at 21°C, this relationship was reversed. Individuals that were bold at 13°C also exhibited the highest metabolic rates at 21°C. Additional metabolic challenges during heatwaves could be detrimental to fitness in bold individuals. Equally, lower metabolic rates at non-stressful temperatures could be necessary for optimal survival as heatwaves become more common. These results provide novel insight into the relationship between metabolic and behavioural plasticity, and its adaptive implications in a changing climate.
The state of an animal prior to the application of a noxious stimulus can have a profound effect on their nociceptive threshold and subsequent behaviour. In mammals, the presence of acute stress ...preceding a painful event can have an analgesic effect whereas the presence of chronic stress can result in hyperalgesia. While considerable research has been conducted on the ability of stress to modulate mammalian responses to pain, relatively little is known about fish. This is of particular concern given that zebrafish (
) are an extensively used model organism subject to a wide array of invasive procedures where the level of stress prior to experimentation could pose a major confounding factor. This study, therefore, investigated the impact of both acute and chronic stress on the behaviour of zebrafish subjected to a potentially painful laboratory procedure, the fin clip. In stress-free individuals, those subjected to the fin clip spent more time in the bottom of the tank, had reduced swimming speeds and less complex swimming trajectories; however, these behavioural changes were absent in fin-clipped fish that were first subject to either chronic or acute stress, suggesting the possibility of stress-induced analgesia (SIA). To test this, the opioid antagonist naloxone was administered to fish prior to the application of both the stress and fin-clip procedure. After naloxone, acutely stressed fin-clipped zebrafish exhibited the same behaviours as stress-free fin-clipped fish. This indicates the presence of SIA and the importance of opioid signalling in this mechanism. As stress reduced nociceptive responses in zebrafish, this demonstrates the potential for an endogenous analgesic system akin to the mammalian system. Future studies should delineate the neurobiological basis of stress-induced analgesia in fish.
Fish are used in a variety of experimental contexts often in high numbers. To maintain their welfare and ensure valid results during invasive procedures it is vital that we can detect subtle changes ...in behaviour that may allow us to intervene to provide pain-relief. Therefore, an automated method, the Fish Behaviour Index (FBI), was devised and used for testing the impact of laboratory procedures and efficacy of analgesic drugs in the model species, the zebrafish. Cameras with tracking software were used to visually track and quantify female zebrafish behaviour in real time after a number of laboratory procedures including fin clipping, PIT tagging, and nociceptor excitation via injection of acetic acid subcutaneously. The FBI was derived from activity and distance swum measured before and after these procedures compared with control and sham groups. Further, the efficacy of a range of drugs with analgesic properties to identify efficacy of these agents was explored. Lidocaine (5 mg/L), flunixin (8 mg/L) and morphine (48 mg/L) prevented the associated reduction in activity and distance swum after fin clipping. From an ethical perspective, the FBI represents a significant refinement in the use of zebrafish and could be adopted across a wide range of biological disciplines.
•Chromatic analysis was successfully employed to measure zebrafish group behaviour.•Groups which had 1, 3 or 6 zebrafish fin clipped exhibited changes in behaviour.•Lidocaine prevented the ...behavioural responses when 1 or 3 fish were clipped.•Chromatic analysis can differentiate zebrafish group responses during welfare challenges.
Zebrafish (Danio rerio) are an increasingly popular model species within a variety of biomedical and neurobiological contexts. Researchers are required to prevent any negative states, such as pain, when using experimental animals to optimise fish welfare but analysis tools for zebrafish are lacking.
The chromatic fish analyser (CFA) is a computer-based monitoring system that has the potential to identify changes in fish behaviour via spatial chromatic analysis of video images. The CFA was used to monitor the behaviour of groups of six fish, where none, one, three or six fish were given a fin clip. Additionally a drug with pain-relieving properties, lidocaine, was administered to determine if this ameliorated any alterations in behaviour. The CFA measured hue horizontally and vertically reflecting the position of the fish in their tank. Saturation (indicates clustering distribution) and lightness were measured to reflect overall zebrafish activity.
Changes in vertical hue demonstrated that all fin clipped animals were closer to the bottom of the tank relative to pre-treatment; this was not observed in control groups, and was alleviated in those treated with lidocaine. Saturation (clustering) and lightness alterations indicated fin clipped groups reduced activity after receiving the fin clip. Lidocaine was effective in preventing the behavioural changes when 1 or 3 fish were clipped.
The CFA proved powerful enough to identify significant changes in behaviour taken directly from video images. With further development this monitoring tool represents a step forward in detecting behavioural changes in groups of zebrafish indicating welfare.
•We investigated how habitat enrichment may promote welfare of captive rainbow trout.•Environmental enrichment promotes recovery following stressful treatments.•Habitat enrichment may not affect the ...magnitude of inter-individual variation.•Painful stimulus appeared to override benefits provided by enrichment.•Enrichment should be implemented in experimental studies using rainbow trout.
The EU Directive on animal experimentation suggests that all protected animals should have enrichment to improve welfare yet relatively little research has been conducted on the impact of enrichment in fish. Studies employing enrichment in zebrafish have been contradictory and all fish species should be provided with species-specific enrichments relevant to their ecology. Salmonids are important experimental models in studies within aquaculture, toxicology and natural ecosystems. This study therefore sought to establish whether an enriched environment in an experimental aquarium may promote improved welfare in rainbow trout (Oncorhynchus mykiss) by enhancing their recovery from invasive procedures. Trout were held individually in either barren (no tank ornamentation) or enriched (gravel, plants and an area of cover) conditions. Recovery rates after a noxious stimulus and a standard stressor were investigated by monitoring behaviour, opercular beat rate and plasma cortisol concentrations. Fish were randomly assigned to one of four treatment groups: Control (undisturbed), Sham (handled but not manipulated), Stress (air emersion) and Pain (subcutaneous injection of acetic acid). The results suggest that for rainbow trout environmental enrichment appears to promote recovery and ameliorate adverse effects following a stressor. However, recovery rate did not differ between environments in the pain treatment groups. Thus environmental enrichment may not be an important factor when the fish is responding to a painful stimulus. These results have important implications for the husbandry and welfare of captive rainbow trout and possibly other salmonids and suggest that enriched environments may be preferable to barren environments in experimental studies.
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 GABAA - 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.
► Boldness influences propensity for behavioural responses to predator threat. ► Bold but not shy trout modified risk-taking behaviour and activity levels. ► Threat induces increased expression of stress- and behaviour-related genes. ► No significant physiological stress response observed in these trout.
Between‐individual variation in behavioural phenotype, termed personality, is an important determinant of how populations cope with acute environmental fluctuation related to climate change.
...Personality in the beadlet sea anemone Actinia equina is linked to genetically distinct morphotypes, which are associated with different heights on the shore. In the intertidal zone, high‐shore environments experience more environmental fluctuation due to longer periods of exposure, and animals adapted to live in these environments are predicted to deal more effectively with environmental perturbation than their low‐shore counterparts.
We collected beadlet anemones of two different morphotypes from three different shore heights. We investigated variation in two behaviours at three different temperatures and in a temporal control treatment where the temperature was not changed: startle response time, the time it took an anemone to re‐extend its tentacles after a threatening stimulus, and immersion response time, the time to re‐extend tentacles after simulated tidal immersion. These behaviours reflect risk‐taking and allow individuals to be categorized as bold, shy or intermediate based upon response times.
Both behaviours showed significant changes as the temperature increased. For immersion response, the morphotype associated with the low‐shore‐lengthened response times at high temperatures. For startle response, all animals lengthened their response times at high temperatures but animals collected from the low‐shore lengthened theirs to the greatest degree. At the individual level, although control individuals exhibited temporal changes in their response times, a clear effect of temperature was present in both behaviours. Shy and bold individuals became more intermediate at higher temperatures in immersion response (this effect was present to a lesser degree in control individuals), while intermediate individuals raised their response times at higher temperatures for startle response.
Given that prolonged tentacle retraction reduces foraging opportunities and can negatively impact respiratory efficiency, our data suggest that some individuals within a single population of A. equina, particularly those associated with the lower shore, may exhibit less effective behavioural responses to temperature shifts than others. These findings demonstrate that acute temperature changes influence risk‐taking, and could have profound short and long‐term implications for survival in the face of climate change.
The authors' research demonstrates that some beadlet anemones may be less able to cope with extreme heat waves caused by climate change. Thus, population‐level conservation strategies may risk leaving the most vulnerable individuals behind, causing a loss of genetic diversity and increasing a population's susceptibility to further environmental change.
•We examined the effect of commonly used anaesthetics on behaviour and physiology of rainbow trout.•Rainbow trout demonstrated low behavioural stress during immersion in 2-phenoxyethanol.•Plasma ...cortisol concentrations were lowest in 2-phenoxyethanol treatment group.•MS-222 administration had the most adverse stress response.•2-phenoxyethanol may be a preferred alternative anaesthetic for use in rainbow trout.
Anaesthetic drugs are commonly administered to fish in aquaculture, research and veterinary contexts. Anaesthesia causes temporary absence of consciousness and may reduce the stress and/or pain associated with handling and certain invasive procedures. The rainbow trout (Oncorhynchus mykiss) is a widely-used model species with relevance to both aquaculture and natural ecosystems. This study sought to establish the relative acute impact of commonly used anaesthetics on rainbow trout when used for anaesthesia or euthanasia by exploring their effects on aversion behaviour and stress physiology. Five widely used anaesthetics were investigated at two concentrations reflective of common laboratory practises: MS-222, benzocaine, 2-phenoxyethanol, etomidate and eugenol. The anaesthetics were administered via immersion and fish were: 1) euthanised with anaesthetic; or 2) allowed to recover from deep plane anaesthesia; or 3) subjected to a conditioned place avoidance paradigm. Behaviour, opercular beat rate and plasma cortisol concentrations and cortisol release rates to water were quantified to investigate the effects of the five drugs. Based upon longer induction to deep plane anaesthesia, and increased plasma cortisol levels post-anaesthesia the widely-used and recommended anaesthetic MS-222 may be relatively stressful for rainbow trout. Whereas 2-phenoxyethanol, due to a combination of quicker induction, reduced aversive behavioural response during anaesthesia and lower post-anaesthesia plasma cortisol levels may be a more advisable alternative. It is crucial for the welfare of fish that the use of anaesthetics is as humane as possible and thus these findings have important implications for the welfare and husbandry of captive rainbow trout.
Boldness is a personality trait that defines how individuals respond to risky situations and has clear fitness consequences. Since the adaptive value of boldness is context dependent, the benefit of ...a distinct personality is less clear when the environment is unpredictable. An ability to modulate behaviour can be beneficial, although as behavioural plasticity itself may be costly this depends on the levels of environmental stability. Both boldness and its plasticity are linked with physiological stress coping mechanisms, whereby animals with reduced glucocorticoid responses to stress are bolder and less flexible in behaviour. We investigated the behavioural changes made by bold and shy rainbow trout, and the magnitude of those changes, in response to predation risk and exposure to two environmental challenges. Behavioural and physiological responses under biotic (either no, predictable or unpredictable predation risk) and abiotic (temperature increase or hypoxia) factors were measured. Boldness was determined using a standard novel object paradigm. In general, after exposure to the treatments, fish exhibited less extreme bold or shy behaviour; the greatest change was observed in fish exposed to hypoxia, or those exposed to high risk particularly in shy fish held at a lower temperature. Higher risk also resulted in increased stress, suggesting that extreme bold or shy behaviour might have been maladaptive under a potential predator threat. These results represent novel evidence that boldness is flexible depending upon particular environmental challenges, with important implications for populations facing environmental extremes caused by anthropogenic activity and climate change.
•Boldness influences individual responses to particular environmental stressors.•Contrary to coping style theory, bold and shy fish were both behaviourally labile.•Risk with increased temperature resulted in a change to intermediate behaviour.•Exposure to hypoxia also results in a shift towards intermediate boldness.•Increased risk caused temperature-dependent activation of the HPI stress response.
Physiological stress responses often correlate with personalities (e.g., boldness). However, this relationship can become decoupled, although the mechanisms underlying changes in this relationship ...are poorly understood. Here we quantify (1) how an individual's boldness (response to novel objects) in rainbow trout, Oncorhynchus mykiss, changes in response to interactions with a population of either bold or shy conspecifics and we (2) measured associated post-stress cortisol levels. Initially-bold trout became shyer regardless of group composition, whereas shy trout remained shy demonstrating that bold individuals are more plastic. Stress-induced plasma cortisol reflected the original personality of fish but not the personality induced by the treatment, irrespective of population personality. Change in boldness of bold trout may indicate preference towards initially subordinate behaviour when joining a new population. However, here we provide further evidence that behavioural and physiological parameters of coping styles may become uncoupled whereby behavioural changes are not correlated with stress responsiveness.
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