The effects of cannabidiol (CBD) in transport water on the behaviour of ornamental fishes

The ornamental fish supply chain has multiple transportation phases which can induce stress in fishes. Previous studies have considered methods of improving welfare during transport, by adding water conditioners based on natural compounds known to have anxiolytic effects. Cannabidiol (CBD) has recently emerged as a compound of interest with beneficial immunomodulatory, anti-inflammatory, and anxiolytic effects in mammals. In the first part of the present study, we identified whether addition of CBD to the transport water of ornamental fishes (at nominal concentrations of 3.9, 7.8 or 15.6 mg/l) had an effect on group behaviour post-transport. Variatus platys were transported for 30 min in bags containing one of five treatment groups (control, solvent control, 3.9, 7.8 or 15.6 mg/l CBD). They were then videoed as a group (15 min) immediately after introduction post-transport into an empty tank, with further videoing performed 30 min and 2 h after release. Behaviours analysed included biting, chasing, erratic movements and time spent immobile. The lowest concentration found to affect a range of behaviours was 7.8 mg/l (the middle concentration). Based on these findings, this concentration was used in a follow-on study to identify whether the use of CBD during transport affected individual behaviour and physiology post-transport. Fish were transported in the same way, and then fish were placed individually into open field arenas immediately after transport and videoed for 15 min. Behaviours analysed in the open field arenas included distance travelled, mean speed, time spent immobile, and time spent in the central zone. Water cortisol and skin mucus quantity were also analysed. CBD significantly affected behaviour post-transport, with those fish exposed to CBD exhibiting significantly reduced stress-related behaviours than those in the control and solvent control groups at both the group and individual level. No effects on mucus or water cortisol were seen. These findings highlight the potential for using CBD within commercial water conditioners to reduce the effects of transport stress for ornamental fishes.