Sharks Sense Prey Using Proton-Conducting Jelly

The sensing organs are found across much of the shark's head, and used to track prey. Matt9122/Shutterstock

The secret to sharks' ability to track and hunt down their prey could all hinge upon a strange type of jelly found in the pores that dot their heads and bodies. Only now, over 300 years after it was discovered, have scientists been able to offer an insight into how this jelly works to conduct the weak electric field of prey that allows the sharks to track them. The work has been described in a new paper published in Science Advances.

All sharks, rays, and skates have a special sensing organ known as the “ampullae of Lorenzini.” These are pores, which can be seen with the naked eye, that form tunnels filled with a clear, viscous jelly and which eventually connect with electrosensitive cells at their base. First described by the Italian physician Stefano Lorenzini in 1678, it took another 300 years before people worked out that they are used by the animals to detect the incredibly weak electric fields produced by the fish and other animals the sharks prey upon.

The jelly is a clear, viscous material found in each pore, seen here on a skate. Erik Josberger

The function of the jelly within the ampullae has not been entirely known, until now. This new study has looked into the properties of this jelly, and discovered that it displays the highest proton conductivity ever reported for a naturally occurring material. “The observation of high proton conductivity in the jelly is very exciting,” explains Marco Rolandi, who co-authored the paper. “We hope that our findings may contribute to future studies of the electrosensing function of the ampullae of Lorenzini and of the organ overall, which is itself rather exceptional.”

The ampullae of Lorenzini, clearly visible on the snout of a tiger shark. Albert kok/Wikimedia Commons

Even though the jelly allows the creatures to sense changes in electrical fields as small as five nanovaults per centimeter, the mechanism behind this has remained elusive. They now think that the high proton conductivity, or ability to conduct positive hydrogen ions, may be down to the keratan sulfate in the jelly. Found in other biological materials, such as the cornea and cartilage, keratan sulfates are large, highly hydrated molecules, which allows for proton conduction to occur along the chains of these bonds.

When compared with artificially produced materials, the researchers found that its conductivity was only 40 times lower than the most state of the art proton-conducting polymer so far developed, known as Nafion. “The first time I measured the proton conductivity of the jelly, I was really surprised,” said Erik Josberger, an electrical engineering doctoral student, and first author of the study. “I didn’t expect a natural material to approach the proton conductivity of an engineered material like Nafion.”

It is thought that this discovery, while helping us to understand the intricacies of how the animals live, could also help in the development of new polymers with high proton conductivity. 

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