Group housed zebrafish displayed less stress and anxiety when undergoing research procedures than their singly-housed counterparts, finds a new study published in Animal Behaviour.

Zebrafish are considered to be a less sentient animal than other common research models, such as rats or mice. Because of this, the number of research projects using these tiny fish has skyrocketed in recent years.

"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," corresponding author, Dr. Lewis White, told ALN.

Conducted at the University of Liverpool and the University of Chester, the study compared how male zebrafish recovered from two common research procedures (anesthesia and fin clipping) when they were housed singly, in pairs, or in a group of six.

"We measured behavioral stress by examining number of erratic movements and time spent in the bottom third of the tank. Behaving erratically is a sign of stress as is avoiding open spaces, both of these behaviors have been validated as stress markers in zebrafish and a variety of other species. We also examined whole body cortisol levels and tank water cortisol levels, cortisol is also known as the stress hormone and its levels increase after exposure to a stressful stimulus," White added.

The individually-housed zebrafish displayed the most stress and behavioral alterations after either anesthesia or fin clipping, while those who lived in group tanks resumed normal behavior more quickly.

"Social housed zebrafish show lower levels of stress compared to those housed individually or in pairs. Returning a fish to a familiar group after they are exposed to a stressful stimulus, such as a laboratory procedure, reduces the magnitude of the stress response and allows stress levels to return to "normal" levels faster," White said.

The research was funded by a NC3Rs project grant.

"This study examined effects of group size on individual zebrafish, much more can be done to improve the welfare of these fish and more research must be carried out if our use of them is going to increase," White concluded.