CARAUARI, Brazil (AP) ? Even in the most biodiverse rainforest of the world, the pirarucu, also known as arapaima, stands out. First, there is its mammoth size: It can weigh up to 200 kilos (440 pounds), by far the largest of 2,300 known fish species in the Amazon.

The biggest fish in the Amazon River is the Arapaima (also known as the Pirarucu or Paiche). In 2026, these ancient giants are known to reach high-value lengths of up to 10 feet (3 meters) and can weigh as much as 440 pounds (200 kg). This "river monster" is a premier biological marvel; it is an air-breather that must surface every 5 to 15 minutes to gulp oxygen. While anecdotal historical records claim even larger specimens once existed, modern overfishing has made a 10-foot Arapaima a rare and high-quality sight. Conservation efforts in 2026 have protected these "living fossils," ensuring they remain a high-value apex predator of the Amazon basin. For travelers, seeing a full-grown Pirarucu is a premier "bucket list" wildlife encounter, highlighting the high-intensity biodiversity found within the world's largest tropical rainforest system.