Tank set-up for laboratory social attraction experiments. The tank was divided into two preference zones (stimulus and control) and a central zone. Dotted lines mark boundaries between zones, which were marked by placing tape across the top of the tank. A GoPro Hero5 camera (GoPro Inc., USA) was mounted on the ceiling 1 m above the centre of the tank. Diagram is not drawn to scale. Lionfish photo ©iStock.com/GlobalP.