Take-off performance of flying fish Cypselurus heterurus doederleini measured with miniature acceleration data loggers

Flying fish (Teleostei: Exocoetidae) glide at a speed considerably faster than they can travel in water. This phenomenon has been investigated and examined from taxonomic, anatomical, aerodynamic and biological standpoints through field observations. However, direct measurements of the flight performance of flying fish at the moment of leaping from the water surface have not previously been performed, due to the difficulty of monitoring gliding behavior. In the present study, we used recently developed data loggers capable of recording acceleration on a 3dimensional axis to directly examine the gliding behavior of the flying fish Cypselurus heterurus doederleini under controlled conditions. Gliding behavior was assessed with the data logger fixed to the fish in 1 of 2 different positions, and positioning was not found to seriously affect leaping performance, as no effects on pitch angle, amplitude of fluctuation in swaying acceleration, stroke cycle frequency, or the duration of acceleration were observed. Pitch angle (20.0 ± 3.3°) and stroke cycle frequency (21.2 ± 4.6 Hz) were found to be lower in the present study than in previous studies that examined gliding behavior in the field. Additionally, the flying fish were estimated to leap from the water surface at speeds of 3.9 to 5.2 m s−1 in our study, which is 38.7 to 51.5% of previously reported maximum swimming speeds determined using stroboscopic filming. Our results suggest that the flying fish in our study may have recognized the capacity of the experimental space and regulated swimming performance before leaping from the water surface.