Do coral reef fish learn to avoid unpalatable prey using visual cues?

Colour and pattern provide important visual cues that affect animal behaviour. Learned avoidance of unpalatable prey by coral reef fish in response to visual cues has been studied before, but visual cues have not been separated from distastefulness to make certain that fish were learning solely in response to visual signals. Here, we used artificial foods to test the ability of wild-caught bluehead wrasse, Thalassoma bifasciatum, a common Caribbean reef fish, to learn to avoid unpalatable prey in laboratory experiments. First, we tested whether the relative position of foods of the same or different colours affected avoidance of unpalatable prey. Next, we tested whether blueheads could learn to avoid different colours of unpalatable prey. These experiments also tested whether blueheads could learn to avoid unpalatable prey against a pre-experimental colour bias. Finally, we determined whether blueheads learn to avoid unpalatable prey more effectively using colour or pattern signals. Fish learned to avoid unpalatable prey using colour independent of prey position, and they learned to avoid some colours (red, blue and orange), but not others (yellow, purple and green), based on visual cues alone. Fish avoided yellow, purple and green coloured prey, regardless of whether they were palatable or unpalatable. Fish only avoided white prey when unpalatable. Fish rapidly learned to overcome a strong pre-experimental bias against red prey. There was no difference in the ability of fish to learn to avoid prey using colour or pattern. We conclude that blueheads learn to avoid unpalatable prey using visual signals alone, that they have different responses to different colours and that they adapt quickly to novel prey appearance. Our results do not support the concept that specific prey colours, such as red or orange, strictly signal a chemical defence, but that blueheads continually assess and adapt to prey palatability using visual cues.