Predators can induce swarming behaviour and locomotory responses in Daphnia

1. Exposure to chemical cues released by fish induced a tendency to form and maintain aggregations in two Daphnia clones originating from habitats inhabited by fish (and invertebrate predators), while Daphnia from a clone originating from a fishless habitat did not aggregate in response to fish cues. 2. Daphnia from one of the two clones responsive to fish cues, also aggregated in response to chemical cues released by invertebrate predators or to a substance released from homogenized Daphnia. 3. Chemical cues released by predators and the substance released from homogenized conspecifics induced a significant decrease in Daphnia's swimming speed and an increased readiness to perform a somersaulting escape behaviour, especially in response to light cues.