Illu-Shoal Choice: An Exploration of Different Means for Enrichment of Captive Zebrafish

SIMPLE SUMMARY: The well-being of captive fish is often undervalued, and additional studies and new tools for enrichment need to be produced. Using 2D shapes of zebrafish filled with three different visual illusions in place of natural striped coloration, we tried to create a realistic dummy conspecific that is able to trigger social response, focusing on perceptual features such as overall shape, depth cues, and dynamic perceptions. When compared with a control stimulus that did not resemble a social companion, zebrafish showed no spontaneous attraction towards the images, either caused by a lack of perception of the illusion or by the fact that the illusory movement did not match the biological movement of real zebrafish. In future studies, we hope that we will manage to achieve this result using various illusory patterns. Creating realistic dummies of zebrafish could improve their well-being by acting as a source of social contact while excluding possible aggressive and stressful interactions. Moreover, it could be used as a reinforcement tool in training procedures. ABSTRACT: Fish of any variety are nowadays being kept captive for several purposes, from recreational to alimentary to research. It is possible that we humans often underestimate or misunderstand the basic, natural needs of the species we use for our purposes. Sociality is likely to play an extensive and fundamental role in the quality of life of animals such as zebrafish. This study aimed to develop a dummy conspecific that included depth and motion illusions in order to assess whether these stimuli could represent a valid alternative to a conspecific in triggering shoaling behaviour in a well-known model in genetics and neuroscience, the zebrafish (Dario rerio). We thus replaced the natural livery of a zebrafish shape with three visual illusions: the Ouchi–Spillmann illusion, which generates an effect of local tilting motion; and another two which should create pictorial cues of tridimensionality. Via a binary shoal choice test, we assessed the time spent close to each of the three artificial dummies compared to neutral control stimuli such as grey ellipses. We found no preference for the illusory patterns, suggesting that the illusion was not perceived or, alternatively, that the perception of the illusion was not enough to elicit recognition of the dummy as conspecific and subsequent social behaviours.