The Amazon Region occupies approximately 7 million square kilometres in the North Central part of South America. Most of it is in Brazil but it also crosses the border of Bolivia, Colombia, Ecuador, Guyana (also a small part of the French Guiana), Suriname and Venezuela. The Amazon represents 58.5 percent of the Brazilian land mass. The Amazon forest contains the largest single reserve of biological organisms in the world. No one really knows how many species there are in the Amazon forest, but scientists estimate that there are between 800,000 and 5 million species living there, amounting to 15 to 30 percent of all the species in the entire world. As naturalists catalogue new species of freshwater fish, their findings suggest that there may be as many as 3,000 kinds of fish in the Amazon's rivers and lakes. Among the specialized fish found in the area are: the pirarucu, said to be the largest freshwater fish in the world with specimens measuring over 6.5 feet (2 metres) in length and weighing 275 pounds (125 kilograms); the tambaqui, a member of the fruit-eating characin family which possesses teeth that can crack seeds as hard as those of the rubber tree and the jauari palm; and the piranha. The ferocity of the meat-eating piranha has been exaggerated. Although it is true that some species in rare circumstances have killed large animals and even people, their behaviour depends on the state of their habitat. In main river channels and in larger lakes they appear to leave swimmers unmolested. Only when they lack nourishment do they become aggressive.