Mangrove Rivulus...

Ever hear the term “A fish out of water”?

Meet the amazing

Kryptolebias marmoratus,
better known as ‘rivulus’

Although uncommon within coastal south and central Florida, the Neotropical killifish Kryptolebias marmoratus is widely distributed. The majority of these tiny fish are gray-brown hermaphrodites, while the rare male has a bright red-orange tint. What's a hermaphrodite? In the case of a mangrove rivulus, the ovulated eggs are self-fertilized resulting in homozygous clones. This convenient feature allows the rivulus to perpetuate when males are scarce. Find out more about this odd fish...

Fish in a tree...

Ever hear the term “A fish out of water”?

It usually implies big problems, but not in the case of an odd fish that lives in the mangroves of the western Atlantic: Kryptolebias marmoratus, or better known as ‘rivulus’. A dedicated group of scientists from diverse locations has spent the last couple of decades studying this interesting creature, braving the mud and mosquitoes in mangroves from Central America to Florida.

Rivulus is probably best known as a self-fertilizing hermaphrodite. But this little (max size: 2.5”) fish is also becoming ‘famous’ for being semi-terrestrial:

Rivulus live in the nasty water of crab burrows and fetid mangrove pools, and when conditions get too bad, they leave the water and hide in damp locations, like piles of leaves or under errant co-conut husks.

In fact, in the lab, D. Scott Taylor found that they could live 66 days out of the water in damp mud: “This is probably the coolest fish around”, Taylor says. “Not only do they have a very bizarre sex life, but they really don’t meet standard behavioral criteria for fishes.”

The definition of ‘fish’ was really stretched when the scientists found that rivulus will also move into decaying logs when their pools start to dry. In both Belize and Florida, the scientists examined dead mangrove logs at the edges of drying pools. The logs had been ‘galleried’ by beetle larvae and termites, leaving a honeycomb of narrow cavities inside. It seems that our intrepid fish will wiggle inside the moist chambers of the logs as the pools start to dry, waiting out the dry-spell, packed together like peas in a pod.

And a bunch of them do this: inside one log (5 ft long X 4” dia) in the Florida Keys, over 100 were found. When the log was carefully broken apart, they came flipping out like so many grasshoppers! Not very characteristic for a fish, would you say?

“This is a classic example of how nuances of natural history can be easily overlooked. In-depth study is required at every level of any organism to dissect out the details”, Taylor said.

Indeed: this may be the first known case of fish living in trees!

Mangrove Rivulus...

A Very Short Silent Movie (51KB)

Flipping Llike Grasshoppers...
Rivulus may be first known case of fish living in trees!

1.5m X 9cm diameter log found in a drying pool in the Florida Keys...upon carefully breaking it open, the many rivulus found inside began flipping out as soon as exposed. About 100 fish were collected from this log.

Video by Ben Chapman

Rivulus Condos...

Ongoing research and breeding program at the Environmentally Endangered Lands Program facility in Melbourne, Florida.

For further information contact D. Scott Taylor at 321-255-4466 or by

Mangrove Rivulus

Get to know this amazing little fish! As research continues, new articles will be added to this library.

Hermaphrodite

Publications

Rare Orange-tinted Male

Other Resource Links

For further information contact D. Scott Taylor
321-255-4466 or