Mudskippers are fish that 'walk' on the mudflats at low tide. There are many kinds. One lives near the high-tide mark and spends most of its time out of water. It must keep its skin moist as that is how it absorbs oxygen. It also absorbs oxygen by keeping its mouth full of water and passing the water over its gills. It feeds on the tiny crabs that inhabit the mudflats. After grabbing one, it must get another mouthful of water. Another mudskipper lives near the low-water mark so is only out of the water for an hour or so each day. It sifts through the mud for small crustaceans and worms. The largest type of mudskipper lives midway between the tide marks and eats algae and other microscopic plants from the mud. It is very territorial about its grazing area and builds walls of mud around them, carrying the mud in its mouth. When two of them meet, a fight will break out with both of them opening their mouths wide and facing off. On clear mud, their territories form a patchwork of walled-ponds. To attract a mate, a male will leap up from the mud hoping to be seen. When a female is finally enticed to a male's pond he will continue his courtship by excitedly flexing his fins and waggling his tail. They will then spawn in a burrow at the bottom of his little pond.