This living fossil breathes through a slit on its head
Bichirs diverged from all other ray-finned fishes at least 330 million years ago, yet still swim African swamps with ganoid scales, fleshy pectoral fins, and paired lungs. They breathe through spiracles on their skull when undisturbed—using a unique recoil-aspiration method found nowhere else among air-breathing fish.
Polypterids—the bichirs and reedfish—are the sole living members of Polypteriformes and the sister group to every other extant ray-finned fish. They inhabit tropical African freshwater, mainly shallow floodplains and estuaries. Their bodies bear seven to eighteen dorsal finlets with spines, rhombic bony scales, and jaw structures closer to tetrapods than to teleosts. Four gill arches remain; two gular plates and paired ventral lungs connect to the esophagus through a glottis.
These are facultative air-breathers. When water is poorly oxygenated, they surface for air; the right lung extends through the full body cavity, whereas the left lung stops at the stomach. Pulmonary arteries branch from the fourth gill arch; oxygenated blood returns via pulmonary veins. Unlike lungfish and tetrapods, their lungs are smooth sacs rather than alveolated tissue. Polypterids uniquely breathe by recoil aspiration, often preferring spiracles over the mouth in shallow water.
Nocturnal predators, they hunt small vertebrates, crustaceans, and insects with exceptional smell. Females lay 100 to 300 eggs over several days. Fossil polypterids appear around 100 million years ago in the Late Cretaceous of South America and Africa; the related Scanilepiformes date from Permian to Triassic. In aquariums they live ten to thirty-plus years and are marketed as dragon bichirs because of their dragonish profile, usually fed on bloodworm larvae, and content to lie on the bottom beside fish too big to eat. Depending on species, adults range from about 25 centimetres to more than a metre long. Fourteen species survive in two genera—Polypterus, the bichirs, and Erpetoichthys, the lone reedfish—while the extinct Bawitius swam in Late Cretaceous Egypt.
Source: Bichir
