Scientists uncover mudskipper spawning mystery

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Mudskippers brood their eggs in air-filled burrows but submerge them in water when they are ready to hatch, a new study on the amphibious fish has shown.

Scientists from the Institute for East China Sea Research at Japan's Nagasaki University studied the Japanese mudskipper, Periophthalmus modestus, and found that the fish had a fascinating strategy for rearing its brood of eggs.

Like other mudskippers, Periophthalmus modestus lives on intertidal mudflats and is adapted to cope with large swings in temperature, salinity and oxygen levels.

The scientists observed that the fish laid its clutch of eggs on the walls of an air-filled mud burrow constructed by the mudskipper.

However, it wasn't known how the eggs could survive in the stinking estuarine water, which can be almost completely devoid of oxygen.

The study found that male mudskippers, which guard the eggs from predators, took regular mouthfuls of air into the burrow and released them into the burrow to prevent the eggs suffocating due to the lack of oxygen.

When the eggs had completed development, the males waited for the next night-time rising tide and then removed the air from the egg chamber causing it to flood with water.

The flood of water induced the eggs to hatch and the fry could then swim free once they'd broken free from their eggs.

The authors said: "P. modestus has developed a reproductive strategy that allows it to nurture eggs in this severe habitat rather than migrating away from the mudflat.

"This requires that mudskipper eggs be specialized to develop in air and that the air-breathing capacity of the egg-guarding male be integrated in a complex behavioural repertoire that includes egg guarding, ferrying air to and from the egg chamber, and sensing O2 levels therein, all in concert with the tidal cycle."

For more information see: Ishimatsu A, Yoshida Y, Itoki N, Takeda T, Lee HJ, Graham JB (2007) - Mudskippers brood their eggs in air but submerge them for hatching. J Exp Biol. 2007 Nov 15;210 (Pt 22):3946-54.