Environmental and behavioural stressors : effects on physiological function in salmonid fish

Social interactions and aggression among salmonid fish are known to induce stress responses, particularly in subordinate fish, and the physiological effects of these stress responses have implications for fish in both aquaculture and natural environments. The physiological responses exhibited by subordinate fish (i.e. those fish that are low ranking in a social hierarchy) vary depending on the nature and extent of the social interaction and can also be influenced by environmental factors. Artificial environments - typically aquaria - generally elicit a larger stress response in the subordinate fish due to the fish being held in close confinement. The present study has clearly demonstrated that the physiological responses to social interaction and the formation of dominance hierarchies in rainbow trout and brown trough are affected by the environment of the fish e.g. whether the environment is artificial or natural, and stable or subject to fluctuations. In an artificial environment, the present study has confirmed that the effects of the social stress encountered by subordinate fish include decreases in growth rate and condition and increases in plasma cortisol but has also demonstrated decreases in the ability to secrete further cortisol and increases in the standard metabolic rate of subordinates. In a semi-natural environment these physiological consequences of subordinance were seen to be reduced; indeed with the presence of environmental perturbations no physiological differences were noted between dominant and subordinate fish. Finally the present study also investigated the role of cortisol in chloride cell proliferation and the determination of social status and concluded that cortisol appears to play a mineralocorticoid role in the proliferation of chloride cells and may also influence the outcome of social interactions

Non-consumptive effects of native and invasive predators on juvenile Caribbean parrotfish

Non-consumptive effects of predators can have important impacts on aquatic food webs, but there are few data on how predators change the behaviour of Caribbean reef fishes. Such changes may include behavioural responses to the invasive predatory lionfish (Pterois volitans/P. miles). This study used an aquarium experiment to examine the behaviour of herbivorous parrotfish (Scarus iseri) in the absence of other fish (control), with a non-piscivore present, and with a predatory threat from a native grouper or lionfish. Treatments were repeated with and without additional parrotfish shelters to examine the potential effects of degraded reefs (loss of refuges). Using video, parrotfish behaviours (sheltering, swimming in open areas, foraging, aggressive conspecific interactions, bite rates, and shoaling behaviour) were recorded for groups of four parrotfish. Compared to the control, the average number of parrotfish hiding was reduced by 65 % and foraging shoals were 10 % larger when threatened by grouper, likely as a specific response to an ambush predator. When exposed to lionfish, parrotfish reduced their bite rates by 50 %, possibly to be more vigilant of this predator’s unique stalking behaviour. The absence of additional shelter had limited effects although parrotfish formed 10 % larger shoals when swimming in open water, potentially as a defensive behaviour because of a perceived lack of refuges. The reduction in parrotfish bite rates caused by lionfish may have important demographic consequences. Furthermore, parrotfishes are important grazers of macroalgae, and these behavioural changes may exacerbate the direct effects of lionfish predation and potentially affect reef benthic dynamics

Do workplace fish tanks influence employee wellbeing and cognitive performance? An embedded mixed-methods study

Evidence from “pet-friendly” workplaces highlights potential benefits associated with taking companion animals to work, including reduced stress among employees. Ornamental fishes carry a much lower risk than other companion animals and may be a suitable alternative in situations where other animals would introduce too great a risk (e.g., allergy, accidental injury). The aim of this study was to investigate whether watching an aquarium during the working day influenced employee wellbeing through the reduction of stress and improvements in stress-related outcomes. An embedded mixed-methods study was conducted, comprising two within-subjects trials (Trials A and B) and a qualitative follow-up. Participants were university employees and research students who participated during their working day. In Trial A (n = 30), the immediate effects of watching live fishes on mood, physiological stress, and cognitive performance were compared with the effects of watching a fish video or resting quietly. Although some outcomes improved from pre- to post-activity, there was no evidence that watching fishes (live or video) had greater effects than resting quietly. In Trial B (n = 27), the effects of repeatedly engaging in the same three activities over several weeks were examined. Watching fish videos was associated with improvements in “high pleasure-low arousal” and overall job-related affective wellbeing, but no further effects of condition were found. Qualitative follow-up data collected from a subset of participants from the experimental trials (n = 13) indicated that all three activities may be beneficial as leaving their desks provided detachment from work for a short period. Qualitative data suggested that live fishes were perceived as more engaging, but this did not translate to quantitative findings. Locating fish aquaria within offices (rather than a separate workplace location) may promote wellbeing by encouraging “microbreaks”; further research is needed to investigate this hypothesis

Unpredictability of maternal environment shapes offspring behaviour without affecting stress-induced cortisol in an annual vertebrate

Exposure of females to stressful conditions during pregnancy or oogenesis has a profound effect on the phenotype of their offspring. For example, offspring behavioural phenotype may show altered patterns in terms of the consistency of behavioural patterns and their average level of performance. Maternal stress can also affect the development of the stress axis in offspring leading to alterations in their physiological stress response. However, the majority of evidence comes from studies utilising acute stressors or exogenous glucocorticoids, and little is known about the effect of chronic maternal stress, particularly in the context of stress lasting throughout entire reproductive lifespan. To bridge this knowledge gap, we exposed female sticklebacks to stressful and unpredictable environmental conditions throughout the breeding season. We quantified the activity, sheltering and anxiety-like behaviour of offspring from three successive clutches of these females, and calculated Intra-class Correlation Coefficients for these behaviours in siblings and half-siblings. We also exposed offspring to an acute stressor and measured their peak cortisol levels. An unpredictable maternal environment had no modifying effect on inter-clutch acute stress responsivity, but resulted in diversification of offspring behaviour, indicated by an increased between-individual variability within families. This may represent a bet-hedging strategy, whereby females produce offspring differing in behavioural phenotype, to increase the chance that some of these offspring will be better at coping with the anticipated conditions

Chronic exposure to stressors has a persistent effect on feeding behaviour but not cortisol levels in sticklebacks

Animals are often exposed to changes in their environment that may be perceived as stressful, leading to an acute stress response, but to which they can eventually habituate. However, if habituation is prevented, for example due to the stressors being diverse and unpredictable in the timing and sequence of their appearance, a state of chronic stress may ensue. Organisms exposed to chronic stressors may show altered patterns of glucocorticoid hormone synthesis as well as changes in behaviour (e.g. activity and feeding), but the exact phenotypic effects of chronically stressful environments remain poorly understood. In this study, we exposed adult three-spined sticklebacks, Gasterosteus aculeatus, to an unpredictable chronic stress protocol over a period of 67 days and measured their response in terms of water-borne cortisol levels and behavioural patterns. We quantified activity and feeding behaviour in two contexts: (1) when the stressors were applied and (2) during the resting period between stressors. We did not observe a significant cortisol elevation following a period of chronic exposure nor any change in cortisol levels in response to an acute stressor. The exposure of fish to chronic stressors led to a decline in latency to feed during the resting periods, indicative of an anticipation of future stressors. We observed an increase in activity levels of the stress-exposed fish, but only during the presentation of the stressors. Organismal response to protracted exposure to stressors is energetically expensive; thus, our results may indicate a trade-off between energy-demanding activities in fish subjected to a chronically unpredictable environment