Shape learning and discrimination in reef fish.

Coral reef fish live in a complex world of colour and patterns. If they are to survive they need to be able to correctly identify the things they see (e.g. predators, prey) and act accordingly (e.g. flee, feed). This paper investigates whether discrimination is limited to ecologically relevant stimuli or is in fact more adaptable. Our work focuses on the reef damselfish Pomacentrus amboinensis. Within a day or two of capture the fish demonstrated an ability to associate an arbitrary stimulus with a food reward and to discriminate the reward stimulus from a distractor matched along various physical dimensions. In our initial experiments the reward was directly associated with the target. In the final experiment, however, the reward was separated from the target in both space and time, thereby eliminating a weakness applicable to the majority of food reward experiments involving fish; namely, the presence of olfactory cues emanating from the feeding tubes. All fish were not only able to solve this task but also showed anticipatory behaviour (also referred to as goal tracking). We conclude that freshly caught reef fish not only are able to quickly learn and discriminate between novel stimuli on the basis of shape but are also able to interpret stimuli as a predictor for the availability of food at a different time and place (anticipatory behaviour).