“A new study shows how an amphibious fish stays alive for up to two months on land. It’s all in the skin. Mangrove killifish are small fish, only about an inch or two long, that live in temporary pools in the coastal mangrove forests of Central and South America and Florida. During dry seasons when their pools disappear, the fish hole up in leaf litter or hollow logs. As long as they stay moist, they can survive for extended periods out of water by breathing air through their skin. But oxygen isn’t the only thing a fish out of water needs to worry about, according to Professor Patricia Wright, a biologist from the University of Guelph, Ontario, who has studied these fish for years. “All cells in the body need the right combination of ions and water for an animal to stay alive,” Wright explains. “Normally, the gills are responsible for these processes in fish. We knew that in mangrove killifish the gills are likely useless on land, so how these fish maintain ion balance out of water was a mystery.”
Wright’s latest research, published in the November/December 2010 issue of the journal Physiological and Biochemical Zoology, shows that the skin of the mangrove killifish picks up the slack for the gills. Through a series of laboratory experiments, Wright and her team found special cells called ionocytes clustered on the skin of the fish. Ionocytes, normally found on the gills of other fish, are the cells responsible for maintaining the right balance of water and salt in a fish’s cells. “We found the mangrove killifish have roughly as many ionocytes on their skin as on their gills,” Wright said. Other fish species have skin ionocytes in larval stages of development, but usually these cells disappear in the skin as the fish develops.”
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