Bichir

The Polypteridae family, which includes bichirs and the reedfish, is the sole family within the order Polypteriformes. These are ancient ray-finned fish. All species live in freshwater across tropical Africa and the Nile River system, favoring swampy, shallow floodplains and estuaries.

These fish have elongated bodies and a row of 7 to 18 small dorsal finlets instead of a single dorsal fin. Each finlet has double-edged tips, and these are the only fins with spines; the rest have soft rays. Their bodies are covered in thick, rhombic, bone-like scales. Their jaw structure is more similar to that of tetrapods than to teleost fish. Bichirs also have other primitive traits, such as fleshy pectoral fins that resemble those of lobe-finned fish. On top of their heads, they have a pair of slit-like openings called spiracles for breathing air. They possess two gular plates and paired ventral lungs. Both lungs are smooth, unchambered sacs. The right lung is larger and runs the length of the body cavity, while the smaller left lung reaches the stomach. Air enters through a slit-like glottis on the underside of the esophagus, leading to the right lung, with a separate opening connecting the right lung to the left. They have four pairs of gill arches. Depending on the species, maximum body length ranges from about 25 cm to over 100 cm.

Polypterids are nocturnal predators, feeding on small vertebrates, crustaceans, and insects. In aquariums, they commonly eat bloodworms. They have an extraordinary sense of smell. For reproduction, a female lays 100 to 300 eggs over several days, which are then fertilized by the male.

These fish are facultative air-breathers, meaning they breathe air from the surface when their water is low in oxygen. Their lungs are highly vascularized for gas exchange. Deoxygenated blood reaches the lungs via paired pulmonary arteries branching from the fourth gill arch, and oxygenated blood returns through pulmonary veins. Unlike most lungfish and tetrapods, their lungs are smooth sacs rather than having alveoli. They are unique in using recoil aspiration to breathe. When undisturbed or in very shallow water where they cannot tilt their body to breathe through their mouth, they prefer to take in air through their spiracles.

Bichirs and reedfish are popular in public and large home aquariums. They are sometimes marketed as "dragon bichir" or "dragon fin" due to their dragon-like look. Although predatory, they are otherwise peaceful and usually rest on the bottom, though they swim more when lots of large plants are present. They make good tankmates with fish that are too large to be prey but not so large as to be predators. Some aquarists note that pleco catfish may eat the slime coat off polypterids. In captivity, they can live 10 to 30 years or more. Heavily planted tanks suit them well, mimicking their natural habitat.

The family Polypteridae contains two living genera, *Polypterus* and *Erpetoichthys*, along with the extinct genus *Bawitius*. The living species include the reedfish (*Erpetoichthys calabaricus*) and various bichirs such as the West African, Guinean, Nile, Congo, saddled, Mokèlé-mbèmbé, ornate, mottled, barred, shortfin, gray, and Teugelsi bichirs, among others. Fossil species are known from the Late Cretaceous of Egypt and the late Miocene.