African lungfishes bore into the bottom of a riverbed or lake bed for their 「dry sleep.」 After burying themselves they become encased in a sheath that gradually hardens. Here they spend the dry season, during which the waterline becomes lower and the riverbed or lake bed finally dries out. The African lungfish generally digs in and encysts in this manner, even if there is sufficient time to swim to deeper waters. African lungfishes also burrow into mud and ensheath themselves under experimental conditions. They have been kept alive in such an induced state for more than two years.
The South American lungfish also bores into the mud in times of water shortage, but it forms no protective sheath. The Australian lungfish never buries itself in this manner.
Studies have shown that the 「dry sleep」 of the African lungfish is induced by a substance that inhibits the fish's normal metabolism.
Extracts from the brains of such sleeping fish injected into rats have caused them to become lethargic; in addition, the body temperature of the rats falls 5° C, and the metabolic rate falls 33 percent. The day after receiving such injections, the rats stop eating. It is believed that the substance responsible for this effect is a protein-like substance.
狗仔卡
