Hydromechanical study of swim-and-glide behaviour on free-ranging flatfish

具有负浮力的海鱼的间歇性游泳行为，如游泳-滑行行为，被假设为节省了在两个点之间移动所需的能量。然而，还没有研究试图在野外证明这一假设。这在一定程度上是由于在公海观察和监测自由放养的鱼类很困难。以往的常规标记实验表明，尽管比目鱼的游动能力和形态特征较差，但有时会远距离迁徙，但在距离放生地点1000公里处重新捕获。为了测量自由放养比目鱼在迁徙过程中的能量成本，了解比目鱼在其迁徙路线上的活动和时间分配是很重要的。利用日本比目鱼的水深和加速度数据记录仪，同时连续记录了自由放养比目鱼的游泳速度、水深、尾拍活动和游泳角。我们估计并比较了在连续游泳和游泳滑行过程中的迁移能量成本。我们首次成功地使用记录仪记录的尾波剖面直接测量了比目鱼的游泳滑行行为。比较连续游和游滑行两种方式的迁徙成本，在距离相近的情况下，采用游滑行的迁徙方式可以减少22.3%的尾羽数量。因此，这种节能策略可以让负浮力的比目鱼远距离迁徙。

Intermittent swimming behaviour of marine fish with negative buoyancy, such as swim-glide behaviour, has been hypothesized to result in a saving of energy required for locomotion between two points. However, there have been no studies that tried to prove this hypothesis in the wild. This has been due in part to the difficulty of observing and monitoring free-ranging fish in the open sea. Previous conventional tagging experiments have indicated that Japanese flounder, Paralichthys olivaceus, sometimes migrated in the far distance, recaptured 1,000 km from the point of release, despite their lower swimming ability and morphological feature without swim bladder.In order to measure energetic cost of free-ranging flatfish during migration, it is important to know the activity and time budgets of flatfish on its migration route. Using a depth and acceleration data-logger on Japanese flounders, we obtained continuous record of swimming speed, depth, tailbeat activity and swimming angle of free-ranging flounders, simultaneously. We estimated and compared the migrating energy costs during continuous swim and swim-glide.We were successful in direct measurement of swim-glide behaviour from flatfish using tailbeat profiles recorded by the logger for the first time. Compared the migration cost between continuous swim and swim-glide, covering similar distance, migration by adopting swim-glide technique resulted in a 22.3% reduction in number of tailbeats. Thus, this energy-saving strategy allows flatfish with negative buoyancy to migrate the long-distance.