At the Everglades Science Center (ESC), staff members have been examining resource availability for nesting birds in Florida Bay for 30 years by sampling prey base fishes in the coastal mangrove zone of the bay.

During these three decades, they have collected 93 species and over 800,000 fish. This year, the team had the opportunity to add a new species to our list, the Mangrove Rivulus (Kryptolebias marmoratus). Never before captured in the traps, this unassuming fish is one of nature’s oddities, with extreme and specialized adaptations to living in the Everglades ecosystem.

The Mangrove Rivulus is one of two self-fertilizing hermaphroditic vertebrates, meaning they do not require a mate to reproduce.   In fact, in Florida, this species has been observed to be 99% homozygous clones. 

However, the most bizarre adaptation this species exhibits remains its ability to live out of the water for up to two months by temporarily modifying their gills to retain water and using their skin for respiration. This specialized adaptation allows the rivulus to slither into the safety of crevices within mangrove prop roots or into crab burrows during seasonal dry-downs while other fish species are being concentrated into smaller and smaller areas of water and becoming easy prey for birds and other predators.

Additionally, the rivulus has been observed literally jumping on land for short periods to catch termites. Eggs of this species are also amazingly drought tolerant.  Development of the eggs will halt if they dry out, and then resume developing once conditions become more favorable.  

As a red mangrove specialist, the rivulus is considered a species of concern by the National Marine Fisheries Service and a rare find for scientists at the ESC.