Effect of group size on avoidance learning in zebra fish,Brachydanio rerio (Pisces: Cyprinidae)

The purpose of this study was to investigate the effect of density of fish on the rate of avoidance learning in a schooling fish. Naive adult zebra fish (Brachydanio rerio) were trained in a two-way aquatic shuttlebox, in isolation, in groups of two, or in groups of five. The number of trials to reach progressively more exacting levels of performance (1, 2, 3, … ,9 consecutive correct avoidance responses on 2 successive days), was used to quantify the rate of learning for individuals in the three groups. Using this measure, individuals in groups of five reached any given level of performance in fewer trials than individuals tested alone, which in turn reached the progressive criteria in fewer trials than individuals tested in pairs. In addition, the mean latency of response to the conditioned stimulus for individuals in groups of five was significantly lower than for individuals tested alone or in groups of two by Day 3 of the experiment. The rate of learning in zebra fish schools at these densities may be due to either a balance between imitation learning and conflict-inhibition among the fish or the elicitation of different behavioral responses by shock, depending upon environmental stimuli.