When a fish has an itch, sharks provide a handy (if risky) scratching post

Embargoed until: Publicly released: 2022-10-20 05:00

Australia; International; WA

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Aussie and US scientists investigated the preferences of fish when it comes to picking an oceanic scratching post to help them remove pesky parasites, and found sharks are the most popular choice. The team provides records of 'scraping behaviour' in several fish species, including tunas, blue sharks, and mako sharks, which they say is likely used for parasite removal. Itchy fish preferred to scratch their heads, eyes, gills and sides, where parasites are commonly found. Preferences varied, but overall, sharks were the most popular scratching posts (not so 'smooth as hell' after all), although smaller fish were less likely to use a shark than larger fish, suggesting bite-size fish may be aware they could become a snack mid-scratch. The parasite removal caused by scratching likely provides a health boost for fish, the researchers say. The decline in sharks in our oceans could have knock-on effects for the fish species that use them for a good scratch, they conclude.