National Geographic : 1972 Jan
STRAIGHT UP a mangrove stem shin nied the little fish, gripping with power ful pectoral fins (left). Hard behind came another, as agile as the first. They were four inch-long mudskippers-land-roving aquatic creatures that abound swamps of Southeast Asia, including Singa pore, my adopted home. Those sweltering quag mires, so ardently avoid ed by most people, have for a decade nurtured a hobby of mine. When I am not teaching medical students at the Univer sity of Singapore, I like to slip away to the water logged lands northwest of the city to observe a galaxy of fascinating in habitants. If time allows, I go farther afield, to the marshlands of the Malay Peninsula or Borneo. At night in the swamp I am drawn to trees that blink in unison with the soft glow of fireflies. For five years I have studied the insects' synchronous flashings and intriguing social behavior, a project recently supported by a National Geographic Society research grant.* By day, brushing away clouds of mosquitoes, I cruise in a sampan or in the mangrove the gills during the mudskipper's hours-long sojourns in the world of air. Early observers, baffled by the mudskip per's land-going ways, concluded that it somehow breathed through its tail by keeping that appendage Who Says Fish Can't Climb Trees? ARTICLE AND PHOTOGRAPHS BY IVAN POLUNIN, D.M. creep afoot along muddy shores. There I delightedly watch the mudskippers. Scampering over the flats and inching up plants, my favorite swamp resi dents forage in the mud for shellfish left by the ebb tide. They surprisingly ignore the man grove periwinkles that share their perch (left). Obviously, a fish that spends more than half its time out of water possesses a special ized breathing technique. Submerged, the mudskipper respires in the usual manner, drawing in water through the mouth and passing it across gill filaments that extract dissolved oxygen. But while most fish cannot keep their gills moist when out of water, and ultimately suffocate, the mudskipper fills its gill chambers with a mixture of air and water when it emerges. This portable life-support system, an "Aqua-Lung" in reverse, moistens Of course, the immersed while lolling on shore-a habit that my observations do not con firm. Later research punc tured the tail-breathing legend, but there remains the possibility that an occasional dipping of the tail may moisten the rest of the fish through capil lary action. Despite their abun dance, mudskippers ex cite little interest locally as food for humans. Once I asked a villager why he didn't catch and cook them. His brow creased in puzzlement as he struggled for an answer: "True, it is a fish.... But it climbs trees. How can you eat a thing like that!" Mudskippers frequent the world's tropics, but the number of species is uncertain. I identified my tree-climbing subject as Periophthalmus chrysos pilos. The generic name refers to its bulging eyes, the specific name to its gold spots. mudskipper is not the only fish that leaves the water. The walking cat fish of Southeast Asia that has invaded Florida waddles onto land for short periods.t And Southeast Asia's climbing perch has been observed following a rivulet of rain water up a slanted tree trunk. But of all fishes, the mudskipper apparently is the most ter restrial, using its forefins like crutches to speed across the mud. Examining its stubby leglike forefins and unique breathing method, I find it easy to see how the ancestors of land creatures crawled out of the water. *In "Nature's Night Lights," GEOGRAPHIC, July 1971, Paul A. Zahl reported discoveries by Dr. Polunin. The London-born physician-teacher holds a Doctor of Medi cine degree from Oxford University. tSee "New Florida Resident, the Walking Catfish," by Clarence P. Idyll, GEOGRAPHIC, June 1969.