Natural World
The Heart of the Ecosystem
Natural Habitats:
Arapaima are native to the Amazon River basin in South America and inhabit a variety of environments, but primarily:
During the dry season, as water levels recede, Arapaima tend to concentrate in larger oxbow lakes and deep river channels.
During the rainy season (November to May), when water levels rise significantly, they migrate laterally into the flooded forest areas, utilizing these newly accessible territories for feeding and parental care, where prey is abundant and varied.
They generally prefer waters with low current velocity and often with abundant floating and emergent vegetation. They are rarely found in the “black waters” of rivers like the Rio Negro, which are nutrient-poor.
Water Parameters and Adaptations:
Arapaima thrive in tropical habitats with consistent water temperatures, ideally ranging from 24 to 30 °C (75-86 °F). They are highly sensitive to cold water and can die if temperatures drop below 16 °C (61 °F). They prefer slightly acidic water, with an ideal pH range of 5.8 to 7.0.
Arapaima are well-adapted to low-oxygen environments, which are common in their native Amazonian habitats, especially in stagnant pools and flooded forests where decaying vegetation consumes dissolved oxygen. Arapaima are obligate air-breathers, meaning they must periodically surface to gulp air to survive. This crucial adaptation allows them to thrive in waters where most fish would perish due to a lack of oxygen. How do they do this?
Modified Swim Bladder: Unlike the simple swim bladders found in many fish for buoyancy, the arapaima’s swim bladder is complex and subdivided into many irregular compartments, which allow it to operate like a simple lung.
Reduced Gills: Their gills have a reduced surface area. While they still use their gills for some gas exchange, their reliance on gills for oxygen uptake is greatly diminished, especially as they mature. In severely oxygen-deficient pools, nearly all oxygen uptake occurs via air breathing.
Bimodal Breathing: Arapaima exhibit bimodal breathing, utilizing both their gills for aquatic respiration and their modified swim bladder for aerial respiration. However, as adults, they are highly dependent on atmospheric air for oxygen. If denied access to the surface, adult arapaima will drown within minutes.
Surface Breathing: They regularly surface to gulp air, making a distinctive sound. The frequency of these breaths is influenced by factors like water temperature (higher temperatures increase metabolic demand and thus breathing frequency) and body size.
This remarkable air-breathing capability allows arapaima to survive in the stagnant, oxygen-poor waters of the Amazon basin, giving them a significant advantage over gill-breathing fish.
Ecology & Behavior:
Diet: The Arapaima is a carnivorous and opportunistic predator in its natural Amazonian habitat. Its diet varies somewhat with its life stage and the availability of prey in its environment. They primarily eat fish, crustaceans, and insects (aquatic and terrestrial).
Arapaima are known to capture small land animals that venture too close to the water’s edge or fall in. This can include: small mammals, birds, and reptiles.
While the male is actively guarding the fry, the female typically circles in the vicinity, acting as a defender against potential predators. She usually leaves the family unit after about a month and often reproduces with other males in the same reproductive season.
Life Cycle, Size, and Growth Rates: Once out of the larval stage, he young fish grow incredibly fast. After 6 months, they are already 50cm in length, and within their first year, they can already reach an average length of 1m or more!
At about 5 years old, they are sexually mature and typically about 1.5m long. After reaching maturity, they continue to grow and a common adult size would be 2m in length and can weigh between 220- 330 lbs.
The largest recorded specimens have been over 3m long and weighed as much as 450 pounds!
Arapaima can live for over 20 years in the wild, though their populations face overfishing and other ecological threats that reduce this considerably.
Infographic showing the Arapaima’s life cycle from egg to adult, including growth rates and lifespan.
