Sharks can help large ocean fish scratch itch: Australian study

SYDNEY, Oct. 20 (Xinhua) — According to a study published Wednesday in the journal PLOS One, sharks are the preferred scraping surface for large pelagic fish, positively impacting teleost fitness by reducing parasite load.

By analyzing video recordings of more than 100,000 individuals across the Pacific, Indian and Atlantic Oceans, Christopher DH Thompson and Jessica Meeuwig of the University of Western Australia found that large open-ocean fish, such as tuna, prefer to scrape on sharks. then sharks. on other fish species.

Tuna were quite orderly, lining up behind the shark and taking turns stroking the tail. Rainbow runners were unruly, forming a school around the back half of the shark and taking turns darting out to bump into its body the researchers said. , in detailing different scraping behavior between different fish species.

They found that pelagic fish, which are hosts to a wide variety of parasites but with few options for removal, tended to scratch their heads, eyes, gill covers and side surfaces — areas most affected by parasite damage.

According to the study, parasites can negatively affect the fitness of their hosts by draining resources and diverting energy from growth, reproduction and other bodily functions. Because shark skin is made up of small tooth-like structures called dermal denticles, it serves as an ideal scratching surface to remove parasites and dead skin, which can help improve the condition and survival of other fish.

In an article released Thursday by the Conversation, Thompson and Meeuwig expressed concern about the rapid decline in shark populations, noting that some species have shrunk by as much as 92 percent off the coast of Queensland in Australia.

“The continued decline in shark populations could have knock-on effects from the loss of relationships like the ones we describe,” the marine experts warned.

“Marine protected areas have been shown to preserve the behavior of sharks and fish. Introducing more of these areas can help restore and maintain this behaviour,” she added.

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