Fish
Silver Arowana
Osteoglossum bicirrhosum · also called silver arowana, dragonfish, monkey fish, aruanã
The silver arowana is a metre-long ribbon of living mercury that patrols the surface of flooded Amazon forest, and it hunts by jumping — launching clear of the water to pick spiders, birds, and bats off overhanging branches. Local people call it the “monkey fish.”
Overview
Silver arowanas live in still and slow blackwater — flooded forest, lagoons, and oxbows — across the Amazon Basin and the Guianas. They are surface predators with an upturned mouth and upward-looking eyes, eating insects, spiders, fish, shrimp, snakes, and small birds, bats, and mammals. The body is a long, compressed silver ribbon up to 1.2 m with two chin barbels.
The leap
An arowana will launch its whole body a metre or more out of the water to seize prey from branches and low foliage — the behaviour behind the name “monkey fish.” Its mouth and eyes are built for watching the surface film.
A father’s mouth
After spawning, the male takes 100-plus huge eggs into his mouth and broods them — then the yolk-sac fry, then the free-swimming young — for about two months, eating little, releasing the juveniles to feed and gathering them back at any threat.
Dragon fish
Its long scaled body and barbels recall a Chinese dragon. The Endangered Asian arowana sells for tens of thousands of dollars, so the abundant, cheap silver arowana is traded as a substitute.
Status
The silver arowana is Least Concern, widespread and common, though heavily harvested as juveniles for the aquarium trade.
Silver Arowana: common questions
Can a silver arowana really jump out of the water to catch prey?
Yes, and it is one of the fish's defining behaviours. A silver arowana cruising just under the surface will launch its entire body vertically out of the water — routinely a metre or more, with reports of higher — to seize insects, spiders, roosting bats, small birds, and snakes from branches and vegetation hanging over the water. In the Amazon this earns it names translating as "monkey fish" or "water monkey." The leap is powered by a flick of the long body and tail, and the fish's upward-tilted mouth and upward-looking eyes are adaptations for spotting and grabbing prey at or above the surface. Aquarium keepers have to use tight-fitting, weighted lids because captive arowanas will jump straight out of an open tank.
Why do male arowanas carry their young in their mouths?
It is a form of parental care called mouthbrooding, and in the silver arowana it is the male's job. After spawning, the male gathers the clutch — around 100 to 200 unusually large eggs, each up to 1.5 centimetres across with a big yolk — into his mouth. He holds them there as they develop, then continues to shelter the hatched fry, which still carry a conspicuous orange yolk sac, and finally the free-swimming juveniles, releasing them to feed and taking them back in at any sign of danger. This goes on for roughly six to eight weeks, during which the male eats little or nothing. Carrying the young in the safest possible place — inside a large predator's mouth — dramatically improves their survival in predator-rich flooded forest.
What is the difference between a silver arowana and an Asian arowana?
They are related surface-hunting, mouthbrooding "bonytongue" fishes but come from different continents and have very different status. The silver arowana is South American, silver-white, grows to about 1.2 metres, is abundant, and is inexpensive and widely traded for aquariums. The Asian arowana (Scleropages formosus) is Southeast Asian, comes in red, gold, and green colour forms, is slightly smaller, and is listed as Endangered and on CITES Appendix I, so international trade in wild fish is banned. Asian arowanas are prized as living symbols of luck and wealth, especially in Chinese culture, and top specimens have sold for tens of thousands of dollars, which is exactly why the cheaper silver arowana is marketed as a "dragon fish" substitute.
Do silver arowanas make good aquarium fish?
They are commonly kept but are only suitable for advanced keepers with a lot of space. A juvenile is small and cheap, but it grows fast to over a metre, needs an aquarium of several hundred gallons with a large footprint and a secure, weighted lid (they are determined jumpers and jumping into a lid can injure the fish, causing the common "drop eye" and jaw problems), pristine warm water, and a carnivorous diet. They are also territorial and generally aggressive toward tank mates. Many arowanas outgrow their owners' tanks and end up rehomed or released, and released arowanas have established or been recorded in the wild in parts of the United States and Asia.