Piranhas glide among the submerged tree trunks of southern Guyana's flooded forests. They spread there with the rising waters that flood the river basins from March to September each year. But now, in December, the water is receding. In the area around the upper reaches of the Essequibo river, the piranhas are isolated in a string of pools. At first this was to their advantage because food was more concentrated. But now they are isolated and short of a meal. Suddenly a sleek, powerful 4 ft (1.2 m) long giant otter snatches a black piranha and crushes it with its strong teeth. The otters find piranhas easy prey to catch in the dwindling water.
There are many types of piranha in the Amazon basin. Some are largely fruit and seed eaters, the largest up to 2 ft (610 mm) long. Others are flesh eaters 4-16 in (100-400 mm) long, including the black piranha and
the voracious red-bellied piranha. They generally eat other fish, but occasionally hunt in large groups and will tackle animals such as capybaras. With their razor-sharp triangular teeth, they shave out small semicircular chunks of flesh, which they shred and swallow. They are said to strip a victim to the bone in minutes.
