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Why is the mangrove killifish unique?

By Chelsie Vandaveer

October 9, 2002

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The mangrove killifish (Rivulus marmoratus Poey) is a peculiar little vertebrate growing to only five centimeters (2 inches). A native of the New World tropics ranging from Brazil through the Caribbean to central Florida, this killifish adapted to surviving in whatever water was available. It is found in ephemeral habitats from saline mangrove swamps to brackish stagnant pools. Often this killifish sets up residence in the burrow of a blue land crab (Cardisoma guanhumi Latreille).

Mudskipper and a Mangrove Crab Hungrily
Eye the Same Dead Fish
Michael Nichols
Buy Photographic Print at AllPosters.com

Blue land crab burrows extend down to the water table. (See Renfield's Garden, October 2, 2002) Neither crab nor killifish are dependent upon each other, but the relationship appears mutually beneficial. When mudflats dry at the end of the rainy season, a crab burrow offers a pool of water for fish that would otherwise be stranded. The killifish in turn feeds on detritus carried by the crab into its 'pool room' which helps maintain the water quality.

With the return of rains or high tides, the mangrove killifish will flip its way across muddy soils to a new pool. According to Bruce J. Turner (The Biology of Rivulus marmoratus, 2002) this killifish "Has been found in flooded tire tracks, also under and inside emergent rotting mangrove logs, in abandoned termite galleries...attached to mangrove leaves in [the] canopy...and flipping along...in a field more than 100 m from water." It will even "survive packed in moist leaves for at least 60 days."

The mangrove killifish does not even need a mate to reproduce. There are male and female mangrove killifish, but most found in Florida are hermaphrodites having ovotestes which produce both eggs and sperm. It is the only vertebrate known to fertilize its own eggs.

The Smithsonian Marine Station at Fort Pierce has an excellent article on the mangrove killifish including photographs of a hermaphrodite and a male. To learn more about this fascinating creature, click on the link:

http://www.sms.si.edu/IRLSpec/Rivulu_marmor.htm

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