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

具有负浮力的海洋鱼类的间歇游泳行为，如游动-滑行行为，被假设为节省两点之间运动所需的能量。然而，目前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观察和监测公海自由放养鱼类的困难。以往的常规标记实验表明，尽管日本比目鱼（parichthys olivaceus）的游泳能力较低，且形态特征为无鱼鳔，但它们有时会在距离放生点1000公里的地方进行长距离洄游。为了测量自由放养比目鱼在迁徙过程中的能量消耗，了解比目鱼在迁徙路线上的活动和时间预算是很重要的。利用日本比目鱼的深度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动速度、深度、尾部活动和游动角度。我们估计并比较了连续游泳和游泳滑行时的迁移能量消耗。我们首次利用记录仪记录的尾拍曲线成功地直接测量了比目鱼的游动-滑行行为。比较连续游泳和游-滑的迁移成本，在覆盖相同距离的情况下，采用游-滑技术迁移可使尾拍次数减少22.3%。因此，这种节能策略允许具有负浮力的比目鱼长距离迁移。

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.