Swimming from coast to coast: a novel fixed-gear swimming gait in fish.

Bluegill sunfish use intermittent propulsion during volitional swimming. The function of this propulsive mode during routine swimming has not been well quantified. At low speeds, propulsive cycle frequencies and amplitudes were constant, and average speed and power output were controlled by modulating coasting duration. This fixed-gear gait may accommodate muscle level constraints on power production. At higher speeds bluegills switched to a mixed power-modulation strategy, increasing speed and power through increased propulsive cycle frequency and reduced coasting time.