Validation of a novel immersive Virtual Reality setup with responses of wild-caught freely-moving coral reef fish

Virtual Reality (VR) enables standardised stimuli to invoke behavioural responses in animals, however, in fish studies VR has been limited to either basic virtual stimulation projected below the bowl for freely-swimming individuals or a simple virtual arena rendered over a large field-of-view for head-restrained individuals. We developed a novel immersive VR setup with real-time rendering of animated 3D scenarios, validated in a proof of concept study on the behaviour of coral reef post-larval fish. Fish use a variety of cues to select a habitat during the recruitment stage, and to recognize conspecifics and predators, but which visual cues are used remains unknown. We measured behavioural responses of groups of five convict surgeonfish (Acanthurus triostegus) to simulations of habitats, static or moving shoals of conspecifics, predators, and non-aggressive heterospecifics. Post-larval fish were consistently attracted to virtual corals and conspecifics presented statically, but repulsed by their predators (bluefin jacks, Caranx melampygus). When simulated shoals passed nearby repeatedly, they were again attracted by conspecifics showing a tendency to follow the shoal, whereas they moved repeatedly to the back of the passing predator shoal. They also discriminated between species of similar sizes: they were attracted more to conspecifics than butterflyfish (Forcipiger longirostris), and repulsed more by predators than parrotfish (Scarus psittacus). The quality of visual simulations was high enough to identify between visual cues - size, body shape, colour pattern - used by post-larval fish in species recognition. Despite a tracking technology limited to fish 2D positions in the aquarium, preventing the real-time updating of the rendered viewpoint, we could show that VR and modern tracking technologies offer new possibilities to investigate fish behaviour through the quantitative analysis of their physical reactions to highly-controlled scenarios.