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.