Yes some fish can live out of water, but for how long depends on the fish: There are 11 genera of fish that can survive out of water for an extended period, some for minutes at a time, and others – mudskippers, for example – for days. Some even breathe air.

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One species is particularly unusual. The mangrove rivulus usually lives in brackish pools but, when conditions dry up, the fish has an amazing survival response: it hides inside logs.

As their pools diminish, these intrepid fish wriggle into moist cavities in rotten wood. Packed in like sardines, they can live here for up to 66 days without even changing their metabolism. In one incident in the Florida Keys, more than 100 individuals were found crammed together inside a single log. Scientists made the discovery by accident after kicking open a lump of wood.

“To our surprise, all these fish flipped out and tried to escape overland,” said Ben Chapman, an ecologist at Leeds University.

The scientists believe that the logs might also serve as boats when storms sweep them out to sea, transporting their fish passengers. But one mystery is how so many fish can pack together in the logs without coming to blows, since the species is usually very aggressive.

“They really don’t meet standard behavioural criteria for fish,” said Scott Taylor of Florida’s Environmentally Endangered Lands Program.

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Main image: © Cardet co6cs, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons

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