The behavioral responses of developing larvae of the zebra fish (Brachydanio rerio) to vibratory stimulation are described. Larvae begin to respond after 4-5 days from the time of fertilization (the approximate time of hatching). Once this response appears, the characteristic movement, the latency of the response, and the sensitivity of the larva to sound do not change for a period of several days. A number of related behavioral changes are observed at the same time the response to sound appears.
The larval startle response is a characteristic pronounced tail flip. It is very similar to the adult startle response which is believed to be mediated via Mauthner's neuron. The data suggest that the usual response may be due to a wave of muscular contractions along one side of the larva, as would be expected to result from an action potential in a Mauthner cell. More complex responses were also observed and are described.