Rare Hermaphroditic Fish Survives in Mangrove Swamps

An extraordinary adaptation has been documented within mangrove forests and salt marshes of the western Atlantic. The Neotropical killifish Kryptolebias (formerly Rivulus) marmoratus is widely distributed, but locally rare, within coastal south and central Florida.

Habitat alteration has affected the species throughout the state, especially on the east coast (Indian River) where the destruction of mangroves and impounding of high marsh for mosquito control has altered and fragmented suitable habitat. Within tropical salt-marsh and
mangrove forests, Kryptolebias marmoratus seems best adapted to certain micro-habitats, specifically those precluding the survival and establishment of competing fishes. On the east coast of Florida, this micro-habitat preference is the land crab (Cardisoma guanhumi) burrow.

In south Florida and the west coast, Kryptolebias marmoratus is most often captured in stagnant pools in mangrove forests. Most populations of Kryptolebias marmoratus in Florida consist of arrays of homozygous clones since the fish self-fertilizes, the only vertebrate known to do so. Theoretically, isolated populations consisting of only a single clone could persist indefinitely. In contrast, in Belize, ~20% of the population are functional males, and in the presence of males, hermaphrodites start functioning as females and lay unfertilized eggs, which the males then fertilize externally. A 're-evolution of sex' in Belize! Why there? We don't know….many enigmas remain. While general questions remain about the adaptive significance of clonal diversity, the mere presence of this novel fish in salt marsh/mangrove habitats may indicate that other aspects of biodiversity are in good "order."

Based on research conducted by D. Scott Taylor, Ph.D. (Brief Bio)
Brevard County Environmentally Endangered Lands Program
E-Mail - D. Scott Taylor

    Additional information can also be found in the following publications:

  • Fish Lives in Logs, Breathing Air, for Months at a Time,
    National Geographic News , November 6, 2007.
  • Biology and ecology of Rivulus marmoratus: new insights and a review. Florida Scientist 63(4):242-255. 2000. D. Scott Taylor.
  • Estuarine reconnection of an impounded mangrove salt marsh in the Indian River Lagoon, Florida: short-term changes in fish fauna, Mangroves and Salt Marshes, March 1998, pp. 29-36, D. Scott Taylor, Gregg R. Poulakis, Sven R. Kupschus, Craig H. Faunce.
  • Rivulus Marmoratus : Ecology of Distributional Patterns in Florida and the Central Indian River Lagoon, Bulletin of Marine Science, 57(1):202-207. 1995. D. Scott Taylor, Wm. P. Davis and Bruce J. Turner.
  • Swamp Sleuth : a biologist reveals how one rare hermaphroditic fish survives a long dry spring, Sea Frontiers, 1995. D. Scott Taylor.
  • Room Without a View : until a curious biologist dipped into its home, a tiny fish led its quirky life in well-hidden secrecy, Natural History, Sept. 1989. D. Scott Taylor.



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