Like A Fish Out Of Water
By Riaz Bhunnoo
I’m not a marine biologist, but I would guess that fish need to be in water to survive, or at least in the vicinity of moisture. It is strange then that scientists recently described a fish that can live completely out of water for months - in none other than a tree.The mangrove killifish (Kryptolebias marmoratus) usually lives in pools of water around mangrove tree roots in swamps. These pools of water are prone to drying up, which in itself is not bad news for the mangrove killifish as it can survive for months on moist areas of land. They do this by altering their gills to retain water and nutrients and excreting nitrogen waste through their skin.
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| This isn't actually a mangrove killifish but it's a close relative |
What astounded scientists, however, was what they found whilst they were wading through the muddy swamps of Belize - hundreds of fish, lined up end to end, inside rotten trunks and branches. The trunks and branches had small channels carved out by insects that were just the right size to accommodate the 5cm fish. It is thought that they spend months out of the water in this way to get their fix of air.
You might wonder how this fish would reproduce when it is stranded so high and dry. Well, in another strange adaptation, it is the only known backbone-containing hermaphrodite that can self fertilise. It can develop both male and female sexual organs and fertilise eggs whilst they are still in the body. The resulting tiny embryos are then released when it is back in the water.
Although the channels inside the logs make the perfect hiding place, the fish are generally packed in like a tin of, ahem, sardines. These aggressive territorial fish therefore have to put up with each other for several cosy months whilst they are stuck in the same rut.
Get more from Riaz or just indulge in something else a bit fishy:
- Wibble wobble - Twelve headed jellyfish
- Hubble bubble - Baby trout from salmon
- Eeny Weeny - Little squirt's big potential
- Icky Dicky - Candirú: the willy fish
Title image: N
Killifish: Howard Jelks/W
Killifish: Howard Jelks/W
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