Estivation begins as water recedes. The fish digs head-first into soft mud, curls with its tail over its head, and exudes mucus that hardens into a parchment-like cocoon leaving a small opening at the mouth. Air reaches the paired lungs through that tube; the gills, reduced in adults, contribute little.
Physiologically the animal changes as much as it changes posture. Oxygen consumption falls to a small fraction of active rates, feeding stops entirely, muscle protein is drawn down for energy, and nitrogen waste is shifted from ammonia to urea, which can be tolerated at high concentration until the rains return and it can be flushed out. Documented survival in the cocoon commonly spans a dry season of several months, with laboratory and anecdotal records well beyond a year.
The frequently repeated claim of four years in dormancy is not well supported by published measurement, and the practical upper limit under natural conditions is not established.