Arapaima  (Arapaima gigas)

The arapaima is classified as Data Deficient (DD) on the IUCN Red List (1) and listed on Appendix II of CITES (3).

The arapaima (Arapaima gigas), or pirarucu as it is known in Brazil, is one of the largest freshwater fishes in the world (3). Its local name derives from the indigenous words for red and fish, a reference either to the striking red flecks on the scales towards the tail or the reddish-orange colour of the filleted flesh (4) (5) (6). For its huge size, the arapaima is sleek and streamlined with its dorsal and anal fin set well back near the tail on its largely grey to green body (2). In common with other fish belonging to the superorder Osteoglossomorph (bony-tongued fish), the arapaima has a tongue with sharp, bony teeth that together with teeth on the roof of its palate are involved in disabling and shredding prey (2) (7).

The arapaima occurs mainly within the Amazon basin floodplain but its exact distribution, particularly in the lower part of the basin, is not known. It has also been recorded in the upper Essequibo basins of Guyana and fossil evidence suggests its historical presence in the Rio Magdelena basin in Colombia (8) (9). Outside of its native range, arapaima has been introduced to waterways in parts of east Asia for fishing and as a result of unintentional aquarium release (10) (11).

The preferred habitat of arapaima fluctuates with the seasons; lakes and river channels are favoured during the dry season, while flooded forests become much more important during the wet season (12) (13).

Aside from its immense size, perhaps the most peculiar trait of the arapaima is a fundamental dependence on surface air to breathe (12) (14) (15). In addition to gills, it has a modified and enlarged swim bladder, composed of lung-like tissue, which enables it to extract oxygen from the air (2) (14). This is an adaptation to the often hypoxic conditions of the Amazon floodplains, but requires the arapaima to surface for air every 5 to 15 minutes (12) (15).

During low-water levels from August to March, arapaima congregate in lakes and river channels. Towards the end of the season between December and March, the adults pair up, build a nest and spawn. The larvae hatch three to five days later, after which the adult female normally leaves the male alone to protect the young. The male is most conscientious in this role, never allowing the offspring more than a metre away. As the water levels rise, the arapaima migrate into the food-rich environments of the flooded forests. Adults aged a year or more feed primarily on other fish, while the diverse diet of juveniles, which remain under paternal care for approximately three months, includes insects, fish larvae and other small organisms. As the waters recede, the adults and juveniles separate and migrate back to the lakes and rivers (12) (13). Sexual maturity is reached after four to five years and average life spans of 15 to 20 years have been recorded in captivity (8) (16).

The need to regularly surface for air means the arapaima, which can yield as much as 70 kilograms of high quality meat (5), is an easy target for fisherman in the shallow waters of the Amazon floodplain (8) (9). Indeed, it formed a significant part of the diet of the indigenous people of the Amazon Basin and was first marketed commercially in the late 18th century (8) (9). However, in the 1960s, following two centuries of extensive exploitation, the arapaima started to become scarce, and by the 1970s was commercially extinct in the vicinity of major Amazonian cities. In 2001, all commercial fishing of arapaima was banned in Brazil outside of a limited number of sustainable reserves, but illegal fishing still continues (8) (15).

The status of the arapaima population in the Amazon basin is unknown and consequently the species is listed as Data Deficient on the IUCN Red List (1) (15). The financial costs of conducting a population census over such a colossal area are prohibitive and monitoring catches is problematic in a trade that is largely illegal (15). Nonetheless, recent studies have been able to show that despite ongoing exploitation, there remain areas with high levels of genetic diversity, particularly within sustainable reserves. From a conservation perspective it has been suggested that increasing the number of sustainable reserves throughout the Amazon will provide a source for re-population of depleted populations in poorly controlled areas (8) (9). Should the need ever arise in the long-term, there is also scope for reintroduction of Arapaima to the wild from successful captive breeding programs (8).

View information on this species at the UNEP World Conservation Monitoring Centre.

For more information on the Arapaima:

• BBC Wildlife Finder:
  http://www.bbc.co.uk/nature/species/Arapaima