Seahorses have a super strong gulp thanks to two spring-like tendons

Seahorses have an unusually powerful way of gulping down prey, and now we know how they do it. They feed in a swift sucking motion powered by two spring-like tendons that simultaneously trigger an upward head sweep and a gulp of water. This allows the otherwise slow, small fish to capture prey in one lightning-fast movement.

The fastest animal movements in the world, from the snapping mandibles of a trap-jaw ant to the powerful punch of a mantis shrimp, are powered by spring mechanisms. Like drawing a crossbow, the animal’s muscles pull tendons into a latched position before releasing the tension in an explosive motion.

Researchers already knew that seahorses had an elastic tendon on the back of their head that pushes their snout upward while feeding, but Roi Holzman at Tel Aviv University in Israel and his colleagues found that this wouldn’t be enough to account for the shear sucking power the small fish can generate.

In a comparison between three seahorse species and 10 other fish that don’t have spring-feeding mechanisms, they found the seahorses could gulp water around eight times faster than would be expected for their mouth size.

To try to identify how this was possible, the researchers illuminated a seahorse as it fed, allowing them to better see through its semi-translucent skin. They then spotted a second tendon, this one below the chin, that could provide the extra oomph.

“We were able to actually see that the tendon contracts, which means that it can store elastic energy,” says Holzman. “This is cool because up until now, we didn’t really know of any elastic energy storage mechanism that serves two purposes,” he says, describing the simultaneous head thrust and water gulp.

“It nicely confirms the hypothesis that not only the rapid movement of the snout, but also the sucking up of food is done by these fishes at very high power,” says Sam Van Wassenbergh at the University of Antwerp in Belgium.

Next, Holzman plans to investigate if seahorse species have different elastic-powered feeding mechanisms depending on their size and prey. “I’m sure that they have some other crazy innovations that we haven’t found,” he says.