Killifish kings of the mangroves
This month a really interesting story has come out about about mangrove killifish. These tiny fish are native to Florida and Central and South America and as their name suggests they live in mangroves in coastal areas. These killifish are really quite amazing because they can survive huge differences in salt levels in the water they live in and can survive *out* of water for up to several weeks!
A team from the University of Guelph in Ontario, Canada wanted to find out how they manage to survive out of water. Most fish can't live out of water because as soon as they're in air, their gills collapse because of the surface tension of the water on them and they can no longer get enough oxygen to survive, get rid of waste product or maintain their internal ion or salt balance. The team led by Danielle LeBlanc hypothesised that the fish must be exchanging water, ions and oxygen across their skin instead. They tested the fish by keeping them in humid air on a moist surface of either fresh or salt water for 9 days, and measuring the physiological changes.
They found that the fish had as many ionocytes - those are cells for exchanging ions and maintaining salt balance in the body - in their skin as in their gills, and that the cells increased in size when the fish were exposed to air. And by using radioactive isotopes of sodium and hydrogen, they showed that ions were definitely being exchanged across the skin when the gills were out of action. This allowed the fish to mostly maintain their ion balance. The gill physiology also changed when the fish were in air, with cells clumping the lamellae together to protect them and reduce the surface area for water loss. Both the changes in the skin and gills were reversible when the fish were put back into water.
So it's great news that we're now understanding the killifish adaptations to cope with this hugely changeable environment of the mangroves a bit better.