How some fish can stay on land up to 2 months

Some species of fish can stay alive for up to two months on land - it's because of their skin, a new study has suggested.

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.

"All cells in the body need the right combination of ions and water for an animal to stay alive. 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," said Patricia Wright, a biologist from the University of Guelph.

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.

The skin of the mangrove killifish is also equipped to help the fish deal with varying salinity, the research found.

When out-of-water fish were placed on a surface moist with salt water, the skin ionocytes got bigger, indicating that they're working overtime to keep the right salt balance.

When those fish were placed back in water, the skin ionocytes returned to normal size.

The findings were published in the journal Physiological and Biochemical Zoology.