Results may be important for design of robotic, self-propelled aquatic vehicles.
The mechanics of how fish use their complex muscle systems is a tantalizing puzzle in animal physiology. These muscles are the fundamental sources that fish use to power steady swimming and bursts of speed to elude predators and to capture prey. Scientists have long predicted that tuna, with their highly streamlined body and elevated internal temperatures, are equipped with a "high performance" muscle system. Tuna, researchers suspected, power their swimming by projecting muscle force from the mid-body, where the muscle is concentrated, back to the tail, which essentially acts as a natural, thrust-producing hydrofoil.
Now, through a study sponsored by the National Science Foundation and conducted at Scripps Institution of Oceanography at the University of California, San Diego, and the National Marine Fisheries Laboratory in Honolulu, researchers have for the first time documented this muscle action in motion. Stephen Katz, Douglas Syme, and Robert Shadwick report their results in the April 12 edition of the journal Nature.
"The anatomy has been known for a long time, especially the idea that the connective tissue architecture in tunas allows muscles to focus their action further down the body," said Shadwick, a professor in Scrippss Marine Biology Research Division. "Weve taken measurements directly from swimming fish to show it working this way."
In other fishes, such as trout and mackerel, swimming muscles are distributed more uniformly along the body. When their muscles shorten and produce power, the burst is seen as a wave of contraction that causes the entire body to undulate.
Tuna, however, contain swimming muscles located primarily in the central part of the body. Tendons that angle to the backbone link the muscle with the tail.