The northern clingfish is a species of salt-water fish that truly lives up to its name. The remarkably strong fish has such high suction powers that it can pick up and hold on to stuff that’s almost 300 times its own body weight. It can easily outperform all sorts of man-made suction cups. Scientists are now actively studying the fish so they can mimic its design and create a new class of suction devices.
There are currently around 160 known varieties of clingfish in the world, each with its own unique characteristics. There’s a tiny one that sticks itself to the individual spines of sea urchins, a deep-sea variety with not much of a sucker, and a giant one that’s about the size of your forearm. One of the most well-known varieties is the northern clingfish, thanks to studies conducted by biologist and researcher Adam Summers, from the University of Washington.
Native to the Pacific Coast of North America, the northern clingfish lives in rocky intertidal environments, where strong waves and currents can toss them out at any moment. In order to survive in its natural habitat, the clingfish has evolved an adhesion disc that covers about a quarter of its belly. Using this disc, it can stick on to almost any surfaces.
“Basically, if they get stuck on a surface, you are going to have to literally yank on them to get them off,” said Adam. “And if you throw them in a bucket with water and then dump it out, you’ll have an empty bucket with nothing but the clingfish inside.” According to Adam, the clingfish has a sucker that’s made out of its own pelvic and pectoral fins, converged into the shape of a disc. Around the edge of this disc are tiny hexagons that look flat to the naked eye.
“But when you look at them under a scanning electron microscope, you see the top of each of those hexagons is a field of spaghetti, of long, thin hairs that are the same aspect ratio and length as the hairs on spiders’ toes or beetles’ feet,” said Adam.
Photo: Petra Ditsche, University of Washington
“This is pivotal in keeping a strong hold. They keep the edges of the disc from sliding, so on a rough surface the hairs interlock with the surface, and by interlocking with the surface they’re able to keep the cup from moving.” Once it holds on, the clingfish is also able to maintain a low pressure inside of the suction zone, which is the reason behind its death-grip.
“There’s several purposes for it,” said Adam. “One is they are able to stick to rocks when they’re in the intertidal, when they’re being battered by waves. So it keeps them still in high-energy environments.” Apart from survival, the clingfish also uses its suction powers to hunt for limpets – round molluscs that cling tightly to rocks.
Photo: Ryan Hawk/Science Friday
“When they see one, they get really close without touching it and then they suck down to give themselves a nice solid launch point. And then they open their mouth and thrust forward while remaining sucked down and jam their lower jaw teeth under the limpet and suck it off the rock.” Caribbean clingfish are fascinating in their own special way – they are too tiny to attack limpets, but the bones that support their gill covers have venomous barbs to compensate.
To find out exactly how clingfish rapidly stick to and release from surfaces of varying roughness with such ease, Adam and his colleagues conducted a test. They made molds of all kinds of sandpaper ranging from the finest to the roughest. They put these molds into a tank filled with water, and stuck man-made suction cups and clingfish on to the surfaces. They used dead clingfish, just to make sure that it was purely the suction mechanism at work.
Then, the team attached harnesses to the fish and suction cups, and used a machine to pull them off, measuring the force required. What they discovered was astounding – the clingfish generated adhesive surfaces 80 to 230 times their own body weight. Compared to the suction cups, the fish were able to cling on to all the surfaces, except the completely smooth ones.