Fish: Bass' Muscles Suck in Prey, Propel Fish

If you've seen fish feeding in aquariums, opening their mouths to suck in floating food or prey, you will have noticed the powerful vacuuming motion that occurs.

It turns out that largemouth bass, for instance, take their wide mouth movements and slurping power from the very same muscles that provide their swimming power, researchers at Brown University have found.

Instead of using head muscles to open the mouth and provide suction, the fish's elaborate arrangement of mouth bones behaves like the passive spokes of an umbrella, driven by the body's swimming muscles. This makes the bass not only a powerful swimmer but a powerful eater.

Researchers first conjectured in the 1950s that a fish's body might contribute to suction feeding, but the idea had never been tested.

Still, "I think everyone would be surprised by the extent to which the swimming muscles are really the source of power," said study co-author Elizabeth Brainerd, professor of ecology and evolutionary biology, in the release.

Researchers suspect that more than 30,000 species of ray-finned fishes are also gulping with the full force of their body muscles.

In order to make their findings, the three Brown researchers recorded highly precise 3-D X-ray videos of three bass eating goldfish. Using a special instrument, they were able to track and visualize how all the bones in a fish head moved. With that knowledge, they could calculate the mouth's change in volume many times a second, as a fish captured its prey. Those measurements, combined with more conventional data on the water pressure in the mouth, allowed researchers to calculate the power involved over the course of feeding, as reported here.

Ultimately, researchers' analysis showed that up to 95 percent of the power required for the suction came from the swimming muscles. The mouth muscles were too weak to produce anything but small amounts of suction.

The fish researchers marveled at the neuromuscular control that the bass must achieve in order to switch from swimming in pursuit of prey to using the same muscles for producing suction. It can be seen in the video on this page.

"It's like they are doing a stomach crunch to open their mouth," Roberts said, in Eurekalerts.