How the first land dwellers adapted to breathe air after emerging from the depths has fascinated us for decades. While many estuarine air-breathing fish have adopted an amphibious life style, absorbing oxygen through blood vessels in the mouth when roaming at low tide, little was known about air-breathing fish that stay put in flooded burrows at low tides. Tomas Gonzales, Masaya Katoh and Atsushi Ishimatsu decided to go down a mudflat near Nagasaki, Japan,to put the aquatic air-breathing eel goby under surveillance(p. 1085).
First the team recorded burrow oxygen levels while waiting for eel gobies to emerge and start breathing; the fish surfaced when the oxygen fell to 13%of normoxic levels. Watching the eel gobies breathe, the team saw that the fish took great gulps of air, holding it in their mouths for up to 25 min before exhaling. Wondering how the fish absorbed oxygen from the mouthful of air, the team looked to see if the eel gobies had converted their mouths into blood-rich impromptu lungs like other air-breathers, but they hadn't. The fish must be using their collapsed gills to absorb oxygen.
Gonzales suspects that breathing air has given eel gobies the upper hand in their rich mudflat homes, allowing them to stay put and reap the ecosystem's benefits at times when other fish would be left high and dry.