Arapaima gigas

Anatomy and morphology

Arapaima can reach lengths of more than 2 m (6.6 ft), in some exceptional cases even more than 2.5 m (8.2 ft) and over 100 kg (220 lbs). The often cited maximum length of 4.5 m (14.8 ft) comes from a single second-hand-report from the first half of the nineteenth century, and is not confirmed. The maximum-cited weight for the species is 200 kg (440 lbs). As one of the most sought after food fish species in South-America, it is often captured primarily by handheld nets for export, by spearfishing for local consumption, and, consequently, large arapaima of more than 2 m are seldom found in the wild today

Ecology

The diet of the arapaima consists of fish, crustaceans, and other small animals. The fish is an air-breather, using its labyrinth organ, which is rich in blood vessels and opens into the fish's mouth, an advantage in oxygen-deprived water that is often found in the Amaerzon River.This fish is therefore able to survive in shallow waters with dissolved oxygen as low as 0.5 ppm.

Reproduction

Due to the geographic range that arapaima inhabit, the animal's life cycle is greatly affected by the seasonal flooding that occurs. The arapaima lays its eggs during the months of February, March, and April when the water levels are low or beginning to rise. They build a nest approximately 50 cm wide and 15 cm deep, usually in muddy bottomed areas. As the water rises the eggs hatch and the offspring have the flood season to prosper, during the months of May to August. Therefore, the yearly spawning is regulated seasonally. The arapaima male is supposed to be a mouthbrooder, like its relative the Osteoglossum, meaning the young are protected in its mouth until they are older. The female arapaima helps to protect the male and the young by circling them and fending off potential predators.

In his book The Whispering Land, naturalist Gerald Durrell reports hearing the tale in Argentina that female arapaima have been seen secreting a white substance from a gland in the head and that their young have been noted seemingly feeding on the substance.

Importance to humans

The arapaima is hunted and utilized in many ways by local human populations. Arapaima are harpooned or caught in large nets and the meat is said to be delicious. Since the arapaima needs to swim up to breathe air, traditional arapaima fishers often catch them by first harpooning them and then clubbing them dead. One individual can yield as much as 70 kg of meat.

The arapaima has also been introduced for fishing in Thailand and Maraysia. Fishing for this species in Thailand can be done in several lakes, where it is not uncommon to see arapaima over 150 kg landed and then released. Special care is needed when dealing with these fish as although they are large they are also hard to deal with, with catch and release after the fish is landed it must be held in a shallow pen/bed for about 3 hours, as this species goes into shock so a careful watch must be kept to make sure that it is coming up for air about every 15 min, if not then the fish can be gently lifted so that its head comes out of the water, when this happens they have a reflex action to breathe. Arapaimas are also known to leap out of the water if they feel constrained by their environment or harassed.

It is also considered an aqurium fish, although it obviously requires a large tank and ample resources. This animal also appears in the pet trade, although to keep an arapaima correctly requires a large tank and can prove quite difficult.

The tongue of this fish is thought to have medicinal qualities in South-America , It is dried and combined with guarana bark, which is grated and mixed into water. Doses of this are given to kill intestinal worms. In addition, the arapaima's bonytongue is often used to scrape cylinders of dried guarana, an ingredient in some beverages, and the bony scales are used as nail files.