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Optimized Fish Head Movements Up Swimming Efficiency
For some time, fish head movements have been seen by scientists as resulting from other undulations that fish bodies go through. And the prevailing thought was that there were no intentional actions being used by fish swimming through the water.
But new findings made by scientists at the University of Florida, working with others from Harvard University, show that fish are actually quite purposed in how they use their heads. In addition, there are actually a few substantial benefits that they gain from controlling their head movements as they travel around.
Fish appear to control the movements of their heads in an effort to save energy and reduce the costs that respiration has on their bodies. These intentional head movements, researchers found, were linked to the pressure and flow of water around fish.
Scientists used a high-speed camera to record the swimming motions of rainbow trout in a flow tank. They also constructed a 3D-printed fish so that they could control its head movements in their tests.
Researchers were able to show that undulation can optimize a fish’s propulsion, sense of flow and respiration all at the same time. These benefits occur without any tradeoffs, scientists found, as long as movements of the head are coupled correctly with body motions.
To back up those results, researchers tracked the timing between side-to-side movements and yaw (rotation) movements as compared to swimming speed. As the speed picked up, so too did that timing. They were then able to pinpoint that muscle groups around fishes’ heads were working the most to achieve the high swimming speeds.
Higher speeds and better timing equal improved swimming efficiency, scientists say, while still maintaining respiration and sensing functions. The motions that fish use to undulate also appear to enhance lateral line sensory function by minimizing the stimulation created by too much movement, according to a model the researchers developed.
For respiration benefits, the same model showed that fish time their breaths to exploit gaps in pressure points around their heads. This also minimizes the energy that would otherwise be needed to pump dense water through their gills.
When the pressure difference between the outside and inside of the fish’s mouths reached 0.2 mmHg, scientists say their test fish simply opened it up and let water come through passively. In this ingenious way, it appears that fish can use the swimming pressures they generate to make pumping unnecessary for gill function.
Results of the study may be useful in discerning how other undulating animals, or even some machines, use movements to save energy. Full findings, including methods and additional conclusions, are published in the journal Nature Communications.
Top image: A 3D-printed fish model helped University of Florida scientists identify the advantages in swimming efficiency fish gain from controlling their head movements. (Credit: Jimmy Liao / University of Florida)