Powell, C., von Keyserlingk, M. A. G., Franks, B. 2021. Tank cleaning temporarily increases stress and decreases affiliative behavior in zebrafish. Applied Animal Behaviour Science 242, 105414.

Small, tropical fish are popular companion animals and constitute a major proportion of the vertebrates used in scientific research, but little is known about how they are affected by routine husbandry practices. Manual tank cleanings are a common and potentially stressful maintenance procedure that involves siphoning out a substantial volume of tank water, ‘vacuuming’ the substrate to remove waste, and pumping fresh water back into the tank. To examine how manual tank cleanings may affect stress and affiliative behavior in zebrafish (Danio rerio), we video recorded the behavior of zebrafish (five 110 L tanks, 10 fish/tank) at two time-points: (i) immediately after tank cleaning and (ii) approximately one hour later. For comparison, we also recorded behavior during time-matched periods the day before cleaning (baseline) and the day after cleaning (longer-term effects). All fish had been exposed to this weekly procedure for over a year prior to data collection. Results show that immediately after tank cleaning, fish spent more time lower in the water column (an indicator of negative affect in zebrafish; p < 0.02), and were less cohesive (p < 0.0001), less coordinated (p < 0.0001) and tended to be more aggressive (p < 0.08) than they were during time-matched baseline periods. An hour after tank cleaning, all behaviors returned to baseline (p’s > 0.2). On the day after cleaning, behaviors during both periods (immediately after and one-hour later) were indistinguishable from baseline (aggression: p > 0.05; all others: p’s > 0.1). These results suggest that fish, like other animals, are adversely affected by some husbandry procedures, but that the effects may be short-lived. Future research could explore ways of mitigating tank cleaning stress by, for example, giving fish more predictability and control over their exposure to the husbandry event.