Downs Abigail M, Kolpas Allison, Block Barbara A, Fish Frank E
Department of Biology, West Chester University, West Chester, PA 19383, USA.
Department of Mathematics, West Chester University, West Chester, PA 19383, USA.
J Exp Biol. 2023 Feb 15;226(4). doi: 10.1242/jeb.244144. Epub 2023 Feb 24.
Tuna are known for exceptional swimming speeds, which are possible because of their thunniform lift-based propulsion, large muscle mass and rigid fusiform body. A rigid body should restrict maneuverability with regard to turn radius and turn rate. To test if turning maneuvers by the Pacific bluefin tuna (Thunnus orientalis) are constrained by rigidity, captive animals were videorecorded overhead as the animals routinely swam around a large circular tank or during feeding bouts. Turning performance was classified into three different types: (1) glide turns, where the tuna uses the caudal fin as a rudder; (2) powered turns, where the animal uses continuous near symmetrical strokes of the caudal fin through the turn; and (3) ratchet turns, where the overall global turn is completed by a series of small local turns by asymmetrical stokes of the caudal fin. Individual points of the rostrum, peduncle and tip of the caudal fin were tracked and analyzed. Frame-by-frame analysis showed that the ratchet turn had the fastest turn rate for all points with a maximum of 302 deg s-1. During the ratchet turn, the rostrum exhibited a minimum global 0.38 body length turn radius. The local turn radii were only 18.6% of the global ratchet turn. The minimum turn radii ranged from 0.4 to 1.7 body lengths. Compared with the performance of other swimmers, the increased flexion of the peduncle and tail and the mechanics of turning behaviors used by tuna overcomes any constraints to turning performance from the rigidity of the anterior body morphology.
金枪鱼以其卓越的游泳速度而闻名，这得益于它们基于尾鳍升力的推进方式、庞大的肌肉质量和刚性的梭形身体。刚体在转弯半径和转弯速率方面应会限制机动性。为了测试太平洋蓝鳍金枪鱼（Thunnus orientalis）的转弯动作是否受到刚性的限制，研究人员在圈养的金枪鱼日常围绕大型圆形水箱游动或进食期间，从上方对其进行了视频记录。转弯性能被分为三种不同类型：（1）滑行转弯，即金枪鱼将尾鳍用作方向舵；（2）动力转弯，即动物在转弯过程中使用尾鳍连续近乎对称的摆动；（3）棘轮转弯，即整个全局转弯是通过尾鳍不对称摆动的一系列小局部转弯完成的。对吻部、尾柄和尾鳍尖端的各个点进行了跟踪和分析。逐帧分析表明，棘轮转弯对所有点来说转弯速率最快，最高可达302度/秒。在棘轮转弯过程中，吻部的全局转弯半径最小，为0.38倍体长。局部转弯半径仅为全局棘轮转弯的18.6%。最小转弯半径范围为0.4至1.7倍体长。与其他游泳者的表现相比，金枪鱼尾柄和尾巴增加的弯曲度以及转弯行为的力学原理克服了前体形态刚性对转弯性能的任何限制。
