Fish
Arapaima
Arapaima gigas · also called arapaima, pirarucu, paiche
The arapaima is a giant of the Amazon — a torpedo-shaped, armour-scaled fish that can grow longer than a person is tall, breathes air with a lung, and has survived largely unchanged since the age of the dinosaurs. It is also a case study in how a fishery can be driven to collapse, and then brought back.
Overview
Arapaima live in the slow rivers, oxbow lakes, and flooded forest of the Amazon basin and nearby drainages. They are built for the dry-season floodplain, when water bodies shrink and stagnate and their oxygen disappears. Where other large fish suffocate, the arapaima thrives — because it does not rely on its gills alone.
An air-breathing fish
The arapaima’s swim bladder is modified into a lung, lined with tissue rich in blood vessels. The fish surfaces every 5 to 15 minutes to gulp air with a distinctive coughing sound. This lets it occupy the warmest, most oxygen-starved water in the system — but it also makes the fish loud and predictable, and traditional hunters simply listen for the gulp and harpoon it.
Armour
Arapaima are covered in large, hard mineralised scales with a brittle outer layer over a flexible collagen underlayer. A predator’s bite cracks the surface but the cracks are absorbed by the tough inner layer, so the scale flexes instead of failing — enough to shrug off piranhas. Materials scientists study arapaima scales as a template for flexible body armour.
Family life
The male guards the young. After the female lays eggs in a nest scraped in the lakebed, the male mouthbroods and shepherds the fry, which swarm in a dark cloud around his head, kept together partly by a chemical his head glands release.
Status
The arapaima is officially Data Deficient — it is really several look-alike species, poorly surveyed. But it has been badly overfished near towns for its large, boneless fillets and has vanished from some rivers. Where community-run fisheries in Brazil enforce annual quotas and protect spawning fish, arapaima numbers have rebounded strongly, making the species a leading example of sustainable Amazon fishing. Introduced arapaima are, conversely, an invasive problem in parts of Southeast Asia.
Arapaima: common questions
How big does an arapaima get?
Reliable modern records top out around 2 metres and 90 to 100 kilograms, but historical accounts and a few exceptional fish reach about 3 metres and 200 kilograms, putting the arapaima among the two or three largest exclusively freshwater fishes in the world, alongside the Mekong giant catfish and the giant freshwater stingray. The very largest individuals are now rare because big arapaima are the prime target for fishing, so the size structure of most populations has shifted downward.
Why does the arapaima have to breathe air?
It lives in Amazon floodplain habitats — oxbow lakes, flooded forest, sluggish backwaters — where the water is warm, still, and often almost devoid of dissolved oxygen, especially in the dry season as pools shrink. The arapaima has converted its swim bladder into a lung-like organ lined with blood-rich tissue, and by surfacing every few minutes to gulp air it can thrive where gill-breathing fish cannot. The trade-off is that it must come up regularly, with an audible gulping cough, which makes it easy for fishers to locate and harpoon.
How are arapaima scales like body armour?
Each scale has a hard, highly mineralised outer shell over a tougher, more flexible inner layer of collagen fibres arranged in criss-crossing sheets. When something bites down, the brittle outer layer can crack, but the cracks are stopped and spread out by the flexible underlayer, so the scale bends rather than shatters and the fish is not punctured. This is exactly the kind of "hard outside, tough inside" layering engineers want in lightweight protective materials, and arapaima scales have been directly studied as a model for flexible armour.
Is the arapaima endangered?
Its global status is officially Data Deficient because the "arapaima" is now known to be several species that are hard to tell apart and poorly surveyed. What is clear is that populations near human settlements have been heavily overfished — the fish is large, air-breathing, easy to find, and its firm, boneless meat is prized — and it has disappeared from some rivers entirely. The encouraging part is that community-managed fisheries in parts of Brazil, which set strict annual quotas and protect breeding fish, have allowed local arapaima numbers to rebound dramatically, making it a model for sustainable Amazon fishing.