Swimming performance of the bluefin tuna: Research with an integrated biomechanics-and biotelemetry-based approach

The purpose of this study is to elucidate The morphology, activityand swimming mechanism of the bluefin tuna by using an integrated biomechanical-andbiotelemetry-based approach. The fluid dynamic properties of bluefin tuna were estimated by计算fluid dynamics (CID) analysis. The coefficients of drag on bluefin tuna decrease asthe fish grows. the drag during swimming depends on the amplitude of caudal-fin oscillation but noton its frequency. The theoretical results of CID revealed that The fish swims with its head tiltedupward during slow cruising in order to maintain mechanical balance with equilibrium state of themoment around its center of gravity. A coupling glide with A large head-tilt angle and upwardswimming with a small angle enable the fish to energetically and efficiently cover long distances.这些theoretical results were确认field data obtained using a data logger that can recordthe depth, head-tilt angle，and tail-beating activity of a tuna during swimming. It is believed that the pectoral fin of thebluefin tuna, owing to its negative buoyancy，produces a lift force that supports the submerged weight of the fish.我们太perfore CIDanalysis to confirm the function of the pectoral fin. For this purpose，我们开发了一个novel data logger that records the movement of the pectoral fin toward or away fromthe body by using a magnetic sensor. the recorded data revealed that the fish often extends its finduring slow swimming in order to produce the required lift force to estimate the efficiency at其中metabolic energy is converted to external work during swimming我们performed experiments using a water tunnel. The cost of transport for a young bluefin tunais approximately 1500j . kg <-1> km <-1>. However, on the basis of the CFD analysis，we estimated the external work for swimming to be 2-4% of the COT；this suggests that the bluefin tuna can use most of its metabolic energy to maintain its bodytemperature。

The purpose of this study is to elucidate the morphology, activity, and swimming mechanism of the bluefin tuna by using an integrated biomechanical-and biotelemetry-based approach. The fluid dynamic properties of bluefin tuna were estimated by computational fluid dynamics (CID) analysis. The coefficients of drag on bluefin tuna decrease as the fish grows. The drag during swimming depends on the amplitude of caudal-fin oscillation but not on its frequency. The theoretical results of CID revealed that the fish swims with its head tilted upward during slow cruising in order to maintain mechanical balance with equilibrium state of the moment around its center of gravity. A coupling glide with a large head-tilt angle and upward swimming with a small angle enable the fish to energetically and efficiently cover long distances. These theoretical results were confirmed by field data obtained using a data logger that can record the depth, head-tilt angle, and tail-beating activity of a tuna during swimming. It is believed that the pectoral fin of the bluefin tuna, owing to its negative buoyancy, produces a lift force that supports the submerged weight of the fish. We therefore performed CID analysis to confirm the function of the pectoral fin. For this purpose, we developed a novel data logger that records the movement of the pectoral fin toward or away from the body by using a magnetic sensor. The recorded data revealed that the fish often extends its fin during slow swimming in order to produce the required lift force. To estimate the efficiency at which metabolic energy is converted to external work during swimming, we performed experiments using a water tunnel. The cost of transport (COT) for a young bluefin tuna is approximately 15000 J・kg^<-1>・km^<-1>. However, on the basis of the CFD analysis, we estimated the external work for swimming to be 2-4% of the COT; this suggests that the bluefin tuna can use most of its metabolic energy to maintain its body temperature.