Differential reinforcement of an approach response in zebrafish (Danio rerio).

Five zebrafish were trained to approach a target using a fully automated training procedure. During a training session, if the distance between the fish and the target was closer than an arbitrarily set distance, the approach response was reinforced by food. The fish continued to respond under this reinforcement contingency and the distance criterion could be shortened up to eighty times within a 1h session. The initial distance limit was then shortened for the next test training session. Once the initial distance criterion was reduced to a final minimum distance, the distance criterion was fixed at this value for the next nine successive sessions. In a second experiment using different fish, we manipulated approach distances in three conditions. The first condition was identical to the changing criterion training as in Experiment 1. In the second condition, only response distances under a distance criterion were reinforced. And in the last condition, only response distances over the distance criterion were reinforced. Results show that zebrafish can control the distance between themselves and a target. In other words, zebrafish are sensitive to the spatial consequences of their behavior. The present results show that a differential reinforcement paradigm can be successfully applied to zebrafish which therefore enhances their value as a vertebrate model for studies of complex behavior including visuomotor learning.