Functional morphology of the flounder allows stable and efficient gliding: an integrated analysis of swimming behaviour

Although technologies such as archival tags have been developed to monitor the behaviour of free-swimming fish, more advanced techniques are required in order to understand the basis of their behaviour. To assess the glide behaviour of the negatively buoyant Japanese flounder Paralichthys olivaceus, we adopted a new approach to examine the importance of the physical aspects of its swimming performance by integrating in situ bio-logging data from free-swimming fish with corresponding computational fluid dynamics (CFD) analyses. Field data from the data loggers revealed that flounder commenced powerless glides after swimming upwards. A theoretical simulation of this glide using CFD analysis revealed that the body angle producing the maximum lift/drag ratio was in agreement with the field data and that, during a glide, the moment equilibrium body angle of the flounder resulted in the longest glide distance. This suggests that the morphology of the flounder confers stability on its glide, making this mode of movement more energetically efficient.