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).