Acoustic telemetry measurement of the use of space by a fish in a large tank

Tank experiments are useful for investigating the responses of fish to external stimuli such as light. We developed a device for monitoring the movement of fish in a large tank (600 m(3)) by using an acoustic transmitter and four hydrophones. On the basis of the differences in sound arrival, which are calculated based on the time at which transmitted signals are detected at each hydrophone, intersections of hyperbolic functions were determined as the position of the fish. An efficiency test of this acoustic telemetry system showed that the device could detect transmitter positions on a two-dimensional coordinate system with accuracy and precision (means) of 0.23 m and 0.02 m, respectively. Observations of the behaviour of Japanese jack mackerel near a fishing light revealed changes in their swimming speed (p < 0.05) and their use of space (p < 0.05). Sonar images from recorded video showed the position of the fish school under various conditions when the transmitter position was estimated using acoustic telemetry to locate the school, assuming that the tagged fish moved along with the school. The results suggest that behavioural measurements obtained using an acoustic telemetry system are effective for understanding the time series of horizontal positions of a tagged fish in a large experimental tank.