Silver Arowana

Overview

The Silver Arowana (Osteoglossum bicirrhosum), celebrated in Brazil as the arawana and known colloquially throughout the Amazon Basin as the ‘water monkey,’ is an ancient, surface-dwelling predatory osteoglossiform fish belonging to the bony-tongued fish family Osteoglossidae. Native to the vast freshwater river networks, blackwater flooded forests (igapo), and floodplain lakes of northern South America—including the Amazon, Orinoco, and Essequibo drainage systems—this prehistoric river giant represents one of the most primitive living lineages of teleost fishes, having remained virtually unchanged since the Jurassic Period.

Renowned for its astonishing aerial hunting capability, Osteoglossum bicirrhosum cruises mere millimeters beneath the water surface, searching for terrestrial prey perched on overhanging branches. Utilizing its powerful, undulating ribbon-like body and broom-like caudal fin, it can launch itself up to two meters (over six feet) completely out of the water into the lower tree canopy to pluck large beetles, katydids, tree frogs, and even resting bats and small birds directly off low branches. Demonstrating extraordinary parental care, adult male arowanas practice obligate oral incubation, brooding hundreds of developing eggs and larvae safely inside their cavernous mouths.

Biology and Physical Characteristics

The Silver Arowana possesses an elongate, ribbon-shaped, laterally compressed body measuring 90 to 120 cm in length. Its body is covered in massive, shimmering cycloid scales that exhibit an iridescent silvery-pearl sheen, reflecting gleaming hints of blue, pink, and gold in tropical sunlight. The dorsal and anal fins are extraordinarily long and set far back on the body, running nearly continuous with the small rounded caudal fin, acting like a flexible paddle that delivers explosive forward propulsion during vertical leaps.

The head is heavily armored with bony plates, featuring an oblique, cavernous, drawbridge-like mouth that opens upward toward the sky. The lower jaw bears two fleshy, sensitive chin barbels that function as hydrodynamic tactile sensors, detecting microscopic surface ripples caused by struggling insects in pitch-black waters. The fish belongs to the archaic order Osteoglossiformes (‘bony tongues’): the roof of the mouth and the large, muscular tongue are studded with sharp, calcified teeth that grind prey against the parasphenoid bone, ensuring immediate crushing of hard beetle exoskeletons before swallowing.

Behavior and Ecology

Silver Arowanas are solitary or loose-schooling diurnal and crepuscular surface hunters that patrol calm riverbanks, oxbow lakes, and submerged rainforests during the annual Amazonian flood pulse. Because dissolved oxygen levels can drop precipitously in warm, weed-choked backwaters, arowanas have evolved the capacity to breathe supplementary atmospheric air: by gulping air bubbles at the surface and forcing them into a vascularized, lung-like swim bladder, they survive in stagnant swamps where other large fishes suffocate.

Reproduction begins at the onset of the wet season when rising floodwaters inundate the forest floor. Courtship involves circling and synchronised flank-slapping, after which the female releases a small clutch of 150 to 250 large, yolk-rich golden-orange eggs measuring over 1 cm in diameter. The male immediately fertilizes them and scoops the entire clutch into his cavernous buccal cavity. For the next six to eight weeks, the dedicated father does not feed, protecting the incubating eggs and yolk-sac fry inside his mouth until the young absorb their yolk sacs and disperse into the flooded vegetation.

Conservation and Human Impact

The Silver Arowana is categorized as Least Concern on the IUCN Red List due to its enormous geographic range across South America and robust wild populations throughout intact Amazonian tributaries. In local river communities, it is a traditional subsistence food fish, harvested by artisanal fishermen using spears and hook-and-line.

However, juvenile arowanas face intense collection pressure for the international ornamental aquarium industry, where glistening baby arowanas are commercially marketed worldwide as miniature dragons and symbols of good fortune. To protect wild stocks from overexploitation, regional governments in Brazil, Colombia, and Peru enforce strict seasonal fishing bans (defeso) during the reproductive brooding period, establish export quotas, and license managed indigenous breeding cooperatives that sustainably harvest juveniles while leaving brooding adult males in wild river sanctuaries.

Interesting Factoid

The Silver Arowana earned the nickname ‘water monkey’ in the Amazon because it can leap more than six feet straight up out of the water like a missile to snatch spiders, tree frogs, and sleeping bats right off tree branches.