Using ultrasound technology, Shadwick and his colleagues attached tiny transducers directly to tuna muscles to record the muscle electrical activity and contraction as tuna swam in a large water tunnel. A device called a sonomicrometer measured the muscle shortening by timing the ultrasound signal between pairs of transducers. That's the essence of how this fish is different from others. Hydrodynamically, that's a more effective way to swim. If all the middle segments throughout the body were undulating, it would create much more drag.
Tunas have a more streamlined body and the motion at the tail acts almost like a propeller.
Shadwick says the results of the study hold implications for research in comparative physiology and the evolutionary biology of fishes. The results also could be important for the design of robotic, self-propelled autonomous underwater vehicles that mimic biological design. The results have prompted Shadwick to move to other species. With new support from the National Science Foundation, he and Scripps researcher Jeffrey Graham have launched a new study to search for the same results in lamnid sharks.