Arapaima

The arapaima (pirarucu in Brazil, paiche in Peru) is native to the Amazon basin floodplains of Brazil, Peru and Guyana, living in slow-moving, often oxygen-deficient rivers and oxbow lakes. It is possibly the largest freshwater fish in the world, reaching up to 3 m and 200 kg, though 2.2-2.4 m and about 90 kg are more common. It is an air-breathing, CITES Appendix II species whose wild populations were commercially extinct near Amazonian cities until managed fisheries restored it.

Adults commonly reach 2.2-2.4 m (7-8 ft) and about 90 kg, with exceptional fish to 3 m and 200 kg; FishBase lists 200 cm as the typical length. Sexual maturity is reached at about 4-5 years, so the adult size must be planned for from the day of purchase. At the common 2 m size the fish already exceeds the length of every home aquarium.

Arapaima are solitary, surface-oriented open-water fish that hunt with sudden gulping strikes - ambush predators who engulf smaller fish. Rising to the surface to breathe is normal behaviour, not stress, because it is an obligate air breather. They may leap out of the water if they feel constrained by their environment or harassed, so cramped or crowded quarters are how escapes happen. Confidence note: medium-confidence guidance drawn from published species care information; treat as conservative guidance, not a precise requirement.

This is not a home-aquarium fish: sources put the practical minimum around 40,000 L (roughly 8 x 2.5 x 2 m), which is pond or public-aquarium scale. It is an obligate air breather, so the surface must stay reachable at all times - any cover must never block access to the air space above the water. It may leap out of the water when constrained or harassed, so the enclosure needs a secure cover with headroom and no open gaps. Confidence note: medium-confidence guidance drawn from published species care information; treat as conservative guidance, not a precise requirement.

Judge the enclosure by usable length and width, not by litre count: a 2 m fish needs a straight, uninterrupted swimming lane several metres long, so a tall, narrow tank is useless even if its volume looks adequate. The footprint implied by a 40,000 L minimum is on the order of 8 m x 2.5 m of floor. Keep hardscape out of the central lane so the fish can turn and accelerate after prey. Confidence note: medium-confidence guidance drawn from published species care information; treat as conservative guidance, not a precise requirement.

Carnivorous: in the wild they eat mostly fish plus fruits, seeds, insects, birds and mammals taken at the surface, gulping prey with a vacuum-like strike. Despite this, arapaima adapt well to commercially available pelleted food, which should form the dietary base in captivity. Do not co-house anything that fits in its mouth - feeding time and tankmate safety are the same problem.

Keep it alone, or with pond fish clearly far too large to swallow - it will eat any tankmate it can swallow, and engulfing smaller fish is its normal feeding mode. In an aquarium this effectively means species-only housing. Invertebrates and bottom-dwellers are prey, not company.

Verdict: skip it unless you can run a 40,000-litre pond or a public-aquarium exhibit - a 1,000 L aquarium will never work, however good the filtration. It needs heavy filtration and careful water-quality management, unobstructed surface access so it can breathe, and a secure cover because it leaps when constrained. Budget for a 20-year, 2-3 m carnivore plus CITES Appendix II paperwork: this is an institutional commitment, not a hobby project. Confidence note: medium-confidence guidance drawn from published species care information; treat as conservative guidance, not a precise requirement.