Mucus lets African lungfish survive drought by forming a protective cocoon around the body.
African lungfish of the genus Protopterus live in freshwater habitats that may disappear during seasonal dry periods. When water levels fall, a lungfish burrows into the mud and secretes mucus that hardens into a cocoon. The cocoon reduces water loss while the fish remains dormant underground.
During aestivation, the lungfish relies heavily on its lungs rather than its gills. It can remain in this state for months, and laboratory observations have shown that individuals can survive much longer under suitable conditions. When rain refills the habitat, the cocoon softens and the fish emerges.
African lungfish are ancient-looking lobe-finned fish and are more closely related to tetrapods than most ray-finned freshwater fish. Their paired fins are narrow and limb-like, while their lung-based breathing demonstrates an important evolutionary transition between aquatic and terrestrial vertebrates.