Seahorses' body shape explained

By Victoria Gill
Science and nature reporter, BBC News

A seahorse's shape enables it to suck in more distant prey

The strange and beautiful seahorse has fascinated people for centuries.

And scientists now say they understand why this unusual fish evolved its equine-like head and S-shape.

A study published in the journal Nature Communications has shown that, compared to straight-bodied pipefish from which they evolved, seahorses are able to strike at more distant prey.

The team concludes that the seahorses' delicate curves evolved to help it hunt and feed.

They attach to seagrass and wait for food to pass by within striking distance Sam Van Wassenbergh University of Antwerp More on seahorses and pipefish from BBC Wildlife Finder

Both seahorse and pipefish feed on tiny marine creatures, striking at them and sucking them into their snouts.

But unlike most pipefish, which swim towards their prey, seahorses sit and wait for their little victims to pass by.

Using high-speed footage and mathematical models, Sam Van Wassenbergh from the University of Antwerp in Belgium showed that the curve in a seahorse's "neck" allows it to strike at more distant prey.

"They rotate their heads upward to bring their mouth close to the prey [passing above]," explained Dr Wassenbergh.

The creatures' curved bodies mean that when they do this, their mouths also moved forward, helping to bring passing small crustaceans within sucking distance of their snouts.

"My theory is that you have this ancestral pipefish-like fish and they evolved a more cryptic lifestyle," said Dr Wassenbergh.

Seahorses evolved from straight-bodied pipefish (left)

This shift in the behaviour to become a more "sit and wait feeder" meant that they needed to capture prey that was further away, he explains.

So these new fish then became S-shaped seahorses, which could use their bodies to strike out.

"They grasp with their tail, to attach to seagrass and wait for food to pass by within striking distance," he says.