Black Arowana

The black arowana (Osteoglossum ferreirai) is a South American bony fish restricted to the Rio Negro basin of the Amazon - blackwater rivers, backwaters and flooded forests. It was only formally described in 1966 and was famously discovered in aquarium trade before its wild population was identified. It is listed as Least Concern by IUCN and reaches about 0.9 m, with reports to 1.2 m.

Adults typically reach 0.9 m (3 ft) with credible reports to 1.2 m, so the profile's 100 cm working figure is fair but leaves no margin - plan the enclosure for 1.2 m. Juveniles are black with yellow markings that vanish at about 15 cm as the steel grey to blue adult coloration develops. Size the tank for the adult from day one, because outgrowing a juvenile setup happens fast.

The black arowana is a solitary surface hunter that usually swims near the top, waiting for shrimps, insects, small fish and anything else floating at the surface to drift into range of its drawbridge mouth. In the wild it is sedentary and non-migratory, patrolling blackwater backwaters rather than roaming. Despite its size it is described as mostly peaceful toward fish it cannot swallow - but anything smaller than its mouth is food, and its leaps make an open lid dangerous. Confidence note: medium-confidence guidance drawn from published species care information; treat as conservative guidance, not a precise requirement.

Plan for an adult around 90 cm (reports to 1.2 m) and a tank of at least 1,500 litres - roughly 2.5 x 1 m of floor - with a secure lid, because they jump like all arowanas. The lid is not optional: South American arowanas are called 'water monkey' because they leap out of the water to take prey, and a startled fish can clear an open top. Provide soft, slightly acidic, very clean water and an unobstructed surface lane, since it hunts at the surface. Confidence note: medium-confidence guidance drawn from published species care information; treat as conservative guidance, not a precise requirement.

Read the 1,500 L minimum as a floor area first: a long, wide box (on the order of 2.5 x 1 m) rather than a tall column, because this fish cruises the surface in straight lines and turns at the ends. Volume alone can be met by a narrow tank that gives a 90-120 cm fish no room to turn. Keep the surface lane clear of hardscape so it can hunt and manoeuvre. Confidence note: medium-confidence guidance drawn from published species care information; treat as conservative guidance, not a precise requirement.

Carnivorous surface feeder: in the wild it eats shrimps, insects, smaller fishes and other animals that float at the surface, captured with a drawbridge-like mouth built for exactly that job. Offer varied meaty foods presented at or near the surface so it can hunt naturally. Every live item must be sized so the arowana can swallow it without injury.

Tankmates must be large and peaceful and physically unable to be swallowed; anything smaller is feed. Juveniles need the same rule plus pristine water, so crowded community setups fail twice over. When in doubt, house it alone - that is how most keepers run the species. Confidence note: medium-confidence guidance drawn from published species care information; treat as conservative guidance, not a precise requirement.

Verdict: an advanced specialist fish - a 90-120 cm predator that needs 1,500+ litres, very clean soft blackwater and a lid that stays shut. Skip it unless you can guarantee stable water quality (juveniles are sensitive to poor water and sudden chemistry swings) and accept that every smaller tankmate is feed. The reward is a striking, iridescent, long-lived surface hunter; the cost is a large, jump-prone, messy predator with almost no margin for error. Confidence note: medium-confidence guidance drawn from published species care information; treat as conservative guidance, not a precise requirement.