The arapaima, one of the world’s largest freshwater fish, is an ancient lineage native exclusively to the Amazon and Essequibo river basins of South America. It has evolved remarkable adaptations to survive in the often-challenging conditions of its tropical habitat. Its existence is deeply intertwined with the ecology and culture of the Amazonian floodplains.
Physical Attributes and Massive Size
Verified specimens reach lengths of up to 3 meters (nearly 10 feet) and weights of 200 kilograms (440 pounds). Its streamlined, torpedo-shaped body is covered in natural armor unique among freshwater fish. The large, overlapping scales are blackish-green across the dorsal side, transitioning to a silver hue on the flanks, with distinct red markings near the tail and along the belly.
This coloration gives rise to its local name in Brazil, pirarucu, meaning “red fish.” The scales are composed of two distinct layers. The outer layer is highly mineralized and corrugated, providing a hard, ceramic-like surface. Beneath this is a tough, flexible layer of collagen fibers arranged in a Bouligand-type structure. This synergistic design allows the scales to flex and deform rather than fracture, making the mature fish virtually impervious to the sharp teeth of piranhas.
The Arapaima’s Obligate Air Breathing
The most distinctive biological feature of the arapaima is its dependence on atmospheric oxygen. The arapaima has a highly modified, lung-like swim bladder. This organ is lined with tissue rich in blood vessels, allowing it to function as a respiratory lung.
Because the stagnant, warm waters of its habitat frequently become hypoxic, the fish must surface regularly to inhale air. An adult arapaima typically breaks the surface every 5 to 20 minutes. This action is accompanied by a distinctive, gulping sound, sometimes described as a cough, as it expels old air and rapidly inhales a fresh breath. If prevented from accessing the surface, the arapaima will drown within minutes, despite possessing gills.
Habitat, Diet, and Parental Care
The arapaima prefers the calm, warm, and often oxygen-depleted environments of Amazonian backwaters, including flooded forests, oxbow lakes, and swamps. It is a generalist piscivore, primarily consuming other fish.
However, its diet is opportunistic and can include crustaceans, insects, and even small terrestrial animals that venture too close to the water’s edge. The species exhibits a profound degree of parental care, beginning with the construction of a nest in the sandy river bottom during the low-water season. The male assumes the primary role of guarding the nest and the subsequent fry, often protecting the young for up to three months.
The male’s devotion extends to helping aerate the water around the nest, which is a necessity for the offspring in the low-oxygen environment. In some instances, the male has been observed using a specialized gland on its head to exude a pheromone, which helps keep the school of young fish in close proximity for protection.
Conservation Status and Aquaculture
Historically, the arapaima was intensely harvested for its boneless, flavorful meat. The fish’s habit of surfacing to breathe made it an easy target for harpoon-wielding fishermen, contributing to localized extinction in many areas. The species is now listed on Appendix II of the Convention on International Trade in Endangered Species (CITES).
Countries like Brazil implemented strict fishing regulations, including outright bans in 1996, and later transitioned to sophisticated, community-based management programs. These management efforts, which include annual censuses and strict catch limits, have led to notable population recovery in managed floodplains. Today, arapaima aquaculture is growing as a sustainable alternative to wild capture, meeting commercial demand while reducing pressure on the recovering natural stocks.