A tiny western Atlantic fish does something never before seen: It makes like a bird, living in mangrove wood for months at a time. A team of U.S. and English scientists accidentally discovered the unique behavior, which they call "logpacking," during recent excursions to Belize and Florida. They were studying how the mangrove rivulus—an animal already infamous for its bizarre sexual behavior—survived the frequent dry spells that strike its swampy forest habitat. "One of us kicked at a log, which broke apart and out came the fish!" said team leader Scott Taylor of Brevard County, Florida's Environmentally Endangered Lands Program. Log-Dwelling Fish The mangrove rivulus, also known as the mangrove killifish, is native to the Americas and is about two inches (five centimeters) long. The fish has long been studied for its many unique features. It's the only vertebrate known to naturally self-fertilize, for example. In some populations, it can become a hermaphrodite, developing both male and female parts simultaneously, to produce clones of itself. (Related: "Sexual Orientation Is Genetic in Worms, Study Says" [October 25, 2007].) The animal can also live out of water for up to 66 days, Taylor said, and is one of very few fish species that spend their entire lives in mangrove swamps. Most fish move in and out of the areas as water sources dwindle.
Taylor and his team had previously found that when small pools of water dried up, the rivulus settled into crab burrows. But even those disappear during extreme dry spells. "Sometimes the pools have very heavy [rivulus] populations, and they have to go somewhere when they dry," he said. "We had seen them under logs and in piles of damp leaves, inside coconuts, even in beer cans—for real."
