Order Osteoglossiformes
Family Arapaimidae
Genus Arapaima.
— Brazilian giant Arapaima, Pirarucu — Arapaima gigas [Schinz, 1822]. Synonym: Sudis gigas, pirarucu, Vastres arapaima, cuvieri, mapae. (English: Giant Arapaima, Pirarucu). South America, Amazon River basin. Reaches a length of 2.5 m. Despite such impressive dimensions, the fish is very graceful and has an attractive appearance. A streamlined body covered with powerful rhomboid scales, a peculiar head shape covered with durable plates, with two small pectoral fins on the sides of the body, and impressive dimensions — all these contribute to the great popularity of the arapaima in large public aquariums around the world.
The front, larger part of the arapaima’s body is olive-green with iridescent golden sheen, acquiring a reddish tint at the level of the unpaired fins, intensifying towards the tail, with orange spots along the body; the belly is white. The caudal fin is dark red. The fin sometimes has a red border. The overlay bones are strongly developed, scales are large, up to six centimeters in large specimens. During the breeding season, males are more colorful, with an exclusively dark head.
These fish are generally solitary, aggressive towards other fish of the same species, and require a very large aquarium. Despite its size, the arapaima is very graceful and highly valued as an aquarium fish. It swims close to the surface, gulping oxygen from the air. In most large aquariums, however, it is considered a very “difficult object” to keep in captivity. The fact is that the arapaima, striving to move in a straight line, forcefully hits the aquarium walls and often dies. This difficulty can be overcome by introducing other fish into the arapaima’s tank, which it will chase while swimming in circles.
They are predators that feed mainly on other fish and small birds. The arapaima grows very fast: young fish (according to observations in the aquarium) grow by 2.5–7.5 cm per month. It feeds on fish and invertebrates. They produce a lot of waste, so special attention must be paid to the levels of ammonia, nitrites, and nitrates in the aquarium. Sexual maturity at 5 years. Young fish remain with their parents for the first 3 months. They live about 20 years. pH 6.0-7.0; T 25-29°C.
Identification: Giant Arapaima — Arapaima gigas.
Genus Heterotis.
— African Nile Arowana, Heterotis — Heterotis niloticus [Cuvier, 1829]. Synonym: Heterotis adansonii, ehrenbergii, Sudis adansonii, nilotica. (English: African Bonytongue, Nile Arowana). Its range, besides the Nile and Lake Turkana, covers a number of rivers in West and Central Africa, notably the Niger, Gambia, Senegal. 70-90 cm. Head is small, eyes are large, anthracite-colored. It has a more rounded head with softer and strongly rounded jaws. The body is long with short dorsal and anal fins, and a spade-shaped caudal fin. Juveniles are colored in monotonous silvery-brown tones with dark streaks on the scales.
As they grow older, the flanks of the fish, depending on their birthplace, begin to cast green or soft blue tints, and the fins gradually color in carrot-orange hues. The general coloration is olive-brown to silver, often with a silvery iridescence. Scales are large, with silver-to-bronze sheen, depending on the region and maturity. Gill covers are covered with an intricate bony pattern with colored veins. Males are brighter and more graceful than females. Adult arowanas resemble pike.
Predators. They do not harm high-bodied fish. Spacious aquariums (from 250 liters) with active filtration are preferred for keeping these fish. They feel great in both soft and hard water, in acidic and alkaline environments. They easily collect dry food from the water surface, and often play with unwary small fish like a cat with a mouse.
They reach sexual maturity at 3-5 years. Spawning is seasonal. Before mating, breeders spend about a week building a bottom nest with plant litter in a shallow planted area, up to 120 centimeters in diameter. The male guards the newly hatched fry. In home conditions, they quickly become tame and recognize their owners even from a distance of a meter. They live 10 years. dH 2-25°; pH 6.5-8.0; T 24-32°C.
Identification: African Arowana — Heterotis niloticus.
Description of the family Osteoglossidae.
Feeding arowanas in an aquarium. 
