Which Fish Can Live Out of Water?
Some species have evolved the ability to breathe air—and literally cross the road.
"Fish out of water" usually means someone who’s totally out of place.
Some fish didn’t get the memo.
For Saturday’s Weird Animal Question of the Week, Ving Salcedo asked what type of fish can live without water for a small period of time. It turns out quite a few have a fin in both worlds.
Out of the Pool to Get Cool
Several fish are amphibious, meaning they can typically survive out of water, Andy Turko, of the University of Guelph in Ontario, Canada, says via email.
Turko co-authored a recent study on the mangrove rivulus, a fish that leaps on land when its tropical waters get too warm. (Related: "To Cool Off, This Fish Leaves the Water.")
Fish use gills to take in oxygen from the water. But many fish, like the mangrove rivulus, have adaptations that let them breathe air.
For instance, mangrove rivulus “have specialized skin that takes on many of the roles of gills,” such as maintaining salt levels, Turko says.
The super skin also has blood vessels that sit within a micron of the skin's surface, allowing more oxygen to absorb into the blood. (See pictures: "Nine Fish With 'Hands' Found to Be New Species.")
The walking catfish, a Southeast Asian native that's invaded South Florida, has an extra organ that supports its gills and helps it take in oxygen from the air.
These Fins are Made for Walking
Oh, and yes, we said walking. (See "Pictures: 'Walking' Fish a Model of Evolution in Action.")
“After a big rainstorm, it’s not terribly unusual to actually see this catfish wiggle across the road," says George Burgess, an ichthyologist at the Florida Museum of Natural History.
The fish flexes its body back and forth to move, and its spiny pectoral fin provides additional leverage.
Eels climb over dams and other obstacles while traveling upstream, breathing oxygen through their skin.
Killifish “flip-flop their way from place to place” on land, and though these movements look random, “they know what they’re doing,” Burgess says. (See "Walking Began Underwater, Strolling-Fish Discovery Suggests.")
A type of killifish called a mummichog navigates visually, jumping up and orienting its body toward the water, according to a recent study.
But West African lungfish blow these other fish out of the water: They have gills and a primitive lung. During dry periods, the animals wrap themselves in a mucus cocoon, burrow into the mud, and lie dormant—sometimes for years.
When rains return and the fish pops back out of the earth, it looks a lot like a "mud pistachio," Burgess says.
Why Do Fish Cross the Road?
Fish leave the water for several reasons, such as escaping predators or low-oxygen environments. Both the snakehead and walking catfish move to “greener pastures” in search of mates, food, or if their current water source is drying up Burgess says. ("Watch: Cave-Climbing Fish Found—Is It Evolution in Action?")
A species called the four-eyed fish climbs onto Brazilian mudflats to feed on insects, Turko notes, and grunion famously come ashore to spawn on California beaches.
So next time you feel like a fish out of water, don’t panic. You might be better off than you think.
Weird Animal Question of the Week answers your questions every Saturday. If you have a question about the weird and wild animal world, tweet me, leave me a note or photo in the comments below, or find me on Facebook.
