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A few dozen species of mudskippers live in mangrove and tidal-zone ecosystems around the world, including on Kuwait’s coast, where it took veteran National Geographic photographer Thomas P. Peschak “many hours of lying motionless in the mud to photograph the courtship rituals” of the fish.

To understand how mudskippers reproduce, scientists need to get dirty

These leaping, googly-eyed fish mate in mud burrows where they adjust water levels to help eggs hatch.

This story appears in the March 2020 issue of National Geographic magazine.

Studying elusive fish that dwell in dark mud chambers is no easy feat. Thus the science of the many species of mudskippers is incomplete—and some of what’s known is a bit odd. Example: Mudskippers of one sort keep their protruding eyes moist by retracting them deep into their sockets and then popping them out again—hence the genus name Boleophthalmus, or “ejected eye.”

When it’s time for these amphibious fish to breed in the tropical intertidal zones where some of them live, the male stages flamboyant courtship displays, flaring his fins and leaping high into the air. If a female’s impressed, she follows the male to a burrow for procreation away from prying eyes. But thanks to an endoscope, excavation tools, and patient research, Atsushi Ishimatsu of Japan’s Nagasaki University and his team have pieced together a vision of how mudskippers reproduce.

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When it’s time for the mudskippers that inhabit Kuwait’s intertidal mudflats to breed, the males try to attract females by erecting their impressive fins. They also leap dramatically into the air in hopes of catching the attention of potential mates from greater distances.

The male builds a burrow to serve as a nest. One or more shafts lead to a chamber that fills partly with water but has a domed ceiling to hold an air pocket. The female deposits eggs on the ceiling, and the male fertilizes them. Once she departs, he tends the eggs for their few days of gestation. To maintain the oxygen the eggs need, the male will swim to the surface, gulp air, bring it back, and exhale, over and over. Watching video that Ishimatsu made with the endoscope, his colleague Karen L. M. Martin deduced that a male might take “roughly 100 mouthfuls” to create the air bubble.

Then somehow, Martin says, the expectant male “keeps track of tide and time”—and at the right moment, he begins gulping the air in the burrow and blowing it out. Water pours in, triggering the larvae to hatch; they swim up from the burrow and away. The male, Martin says, is “really a very good papa.”

Mudskipper Mating

Mudskippers are the only fish that mate out of the water.