Meeting Abstract
Tuna have laterally projecting wings of soft tissue at the narrowing of their body just anterior to their tail in the region of the caudal peduncle. These features are known as keels and have evolved independently multiple times in fast swimming bony fishes and in lamnid sharks. We use micro CT, histology, and simple robotic models to understand the morphology and function of these keels in tunas of the genus Thunnus. In these fishes, keels are extremely flexible and are composed largely of collagen with a cartilage rod running anterior to posterior. Previous research has suggested that lateral keels might decrease lateral forces experienced near the tail and reduce caudal torque of these high-performance fish by streamlining the caudal peduncle in the lateral direction. We test this hypothesis for the first time using simple physical models of tuna-like tails with and without lateral keels. We actuate these model tails in a flow tank using biologically relevant parameters based on kinematic data collected from captive tuna, and we compare performance of models with and without keels. Multi-axis force-torque sensors allow us to compare forces in the drag, thrust, and lateral directions to help elucidate any performance benefits of lateral keels. In addition, we can record and compare mechanical power consumption and self-propelled speed of keeled and keel-less models at a range of motion parameters and speeds. Experimental cases where keeled models outperform keel-less models can be further studied by imaging flow using particle image velocimetry.
