According to an article in WAtoday, itchy fish can go to extreme lengths in the search for the perfect scratching post.

A research paper published in the journal PLOS ONE, suggests innovative ocean-going fish frequently rub themselves against predatory sharks in an effort to remove dead skin and parasites.

While it may sound risky, marine ecologist Dr Chris Thompson, who’s documented the behaviour off Western Australia, Ascension Island in the South Atlantic and off Mexico’s Pacific, claims the sharks seem unphased.

“If you think about it, if you’re offshore, there’s not really anything to scrape against,” said Thompson.

“In inshore environments, sometimes fish will scrape against the sand, or against rocks, there’s one paper that documents them scraping against turtles. And there are cleaner wrasses in reef environments that take dead skin and parasites off fish.

“But offshore, if you don’t have any hands, and you don’t have anyone else to scratch your back, I guess those nice, sandpapery sharks become a bit more attractive.”

Their determination of fish to bump their heads, eyes, gills and sides against the sharks strongly indicates the behaviour is about dislodging parasites, because that’s where fish typically carry them.

The behaviour can be witnessed throughout a variety of species - each displaying distinctly different techniques to get what they want and avoid the toothy end of the shark.

“The tuna were actually really orderly. They’d always come up from behind the shark, fairly quickly, and stop and hold position just behind the tail,” said Thompson. “They seemed to be waiting until the tail was in the perfect position, then they’d speed up again and rub the side of their head or undersurface against the tail and shoot out to the side, away from the shark.”

What’s more, it seems the brave tuna were happy to wait within proximity to the shark for their turn. “If there were multiple tuna they’d go back to the end of the queue, and start lining up again,” he said.

But, not all species shared this methodical approach, with rainbow runners proving particularly shambolic. “They were quite unruly,” he said. “They’d just kind of form a school around the back half of the shark and they’d dart out and hit different parts.”

Still, despite these occasionally chaotic scenes, Dr Thompson has yet to see a single fish fatality as a result of this behaviour. He suggests this could be because the sharks are accustomed to fish schooling close-by, or because the footage was taken using baited cameras, so the sharks attention may have been focused elsewhere.

Since Thompson wrote the paper, researchers have started sharing stories about fish displaying similar behaviours around the world.