How different is a 3D-printed replica from a conspecific in the eyes of a zebrafish?

Robotics is emerging as a promising tool for aiding research on animal behavior. The possibility of generating customizable, controllable, and standardized robotic stimuli has been demonstrated through a number of behavioral assays, involving vertebrates and invertebrates. However, the specific appraisal of the nature of robotic stimuli is currently lacking. Here, we attempt to evaluate this aspect in zebrafish, through a within-subject design in which experimental subjects are faced with three experimental conditions. In the first test, we investigated sociability by measuring zebrafish response to a conspecific separated by a one-way glass. In the second test, we studied zebrafish behavior in response to a 3D-printed zebrafish replica actuated along realistic trajectories through a novel four-degree-of-freedom robotic platform. Last, we investigated fear responses in a shelter-seeking test. In agreement with our expectations, zebrafish exhibited an equivalent preference for live and robotic stimuli, and the degree of preference for the robotic replica correlated negatively with the individual propensity to seek shelter. The equivalent preference for the replica and conspecific suggests that the appraisal of the target stimuli is analogous. The preliminary evidence of a correlation between behavioral responses across tests points to the readability of robotics-based approaches to investigate interindividual differences.