Jack S. Thomson

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

Boldness, a measure of an individuals propensity for taking risks, is an important determinant of fitness but is not necessarily a fixed trait. Dependent upon an individuals 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.

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.

Environmental change alters personality in the rainbow trout, Oncorhynchus mykiss

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.

Stress Management and Welfare

1. Introduction 1.1. Defining Welfare 2. Managing Stress in Fish 2.1. Considerations for Care of Wild Fish in Captivity 2.2. The Impact of Psychological Stress 2.3. Controlling and Preparing for Stress 3. The Impact of Stress on Fish Welfare 3.1. Stress in Fisheries 3.2. Stress in Aquaculture 3.3. Stress in Recreational Fishing 3.4. Stress in Ornamental Fish 3.5. Stress in Research Within a Laboratory Context 3.6. Stress and Welfare in Wild Fish 3.7. Surgery and Anesthesia 4. Conclusions and Future Directions Stress poses a significant challenge to the health and welfare of fish in a variety of contexts. Preserving fish well-being has obvious benefits for aquaculture, fisheries management practices, large-scale fisheries, recreational fishing, research, and the ornamental fish industry. Healthy fish provide better economic return, contribute to population size, provide experimentally sound data, are attractive and pleasing to watch, and pose no risk to public health. However, many practices in each of these areas where fish are used cause stress and as such may impair fish welfare. The impact of routine procedures that fish are subject to is discussed to better understand how stress can be managed in captivity. The means of reducing stress and its deleterious effects on fish behavior, development, growth, reproduction, and immune function are considered as practical management tools that could be employed by those using fish if they wish to minimize stress and improve health. The opportunity to have a sense of control over stress or being able to anticipate and prepare for stress improves the ability of fish to cope with any stressors in their environment. Inescapable, unpredictable, or chronic stress leads to loss of control and allostatic overload. This can result in behavioral abnormalities leading to displaced aggression and stereotypical behavior. Thus, allowing fish to have other behavior options such as hiding or redirecting behavior can be provided by environmental enrichment. Conditioning fish to associate cues with the onset of a stress allows them to anticipate and prepare for stress, which can be beneficial. Operant conditioning, where fish can operate self-feeders, allows fish to control their own foraging behavior and also has positive effects on fish welfare. Providing the right kind of environmental and cognitive stimulation along with optimal environmental conditions, appropriate feeding regimes and social contact appear to be key to reducing stress in captive contexts if this is logistically possible. Practices in a variety of fish industries are considered where stress may be elevated with countermeasures suggested. Future studies should investigate implementing these factors to understand their impact in different circumstances and in different species if reducing stress is important. The development of robust stress indicators and automated alert systems based on behavior or environmental parameters to detect fish health will be vital for the assessment and alleviation of stress.

The impact of social context on behaviour and the recovery from welfare challenges in zebrafish, Danio rerio

Understanding how animals experience stress in a laboratory environment is crucial for improving their welfare. Increasing numbers of fish are being used in scientific studies and further research is required to ensure appropriate conditions are used to promote good conduct and correct housing as well as guaranteeing scientifically valid results. As zebrafish are a gregarious species, social enrichment is particularly important, with individuals separated from a group experiencing isolation stress. The present study aimed to determine the effects of social context on recovery from common laboratory procedures. Additionally, we investigated whether the noninvasive measure of water-borne cortisol can be utilized to gauge physiological stress by comparing it to an invasive measure, whole-body cortisol concentration. Zebrafish (AB strain, male) were housed in differing social contexts and were randomly assigned to one of three treatment groups: undisturbed, anaesthetized and handled, or anaesthetized and fin clipped. Behavioural and physiological stress indicators were recorded before and after treatment. The results indicated social context, in the form of group housing, was important in enhancing recovery from welfare challenges in zebrafish, since group-housed fish resumed normal behaviours more quickly than pairs or individuals. Moreover, the strong correlation between water-borne and whole-body cortisol suggests that the noninvasive measure is an appropriate ethical alternative as an indicator of physiological stress. These findings represent an important refinement in reducing the severity of stress through housing zebrafish in their original groups and by adopting a noninvasive measure of cortisol which will act to reduce the numbers of individuals required for time series studies on physiological stress.

HPI reactivity does not reflect changes in personality among trout introduced to bold or shy social groups

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.