PLANET EARTH Freshwater
Usually, these mountain streams only provide enough food for small animals to survive. But with the spring melt here in Japan monsters stir in their dens. Giant salamanders（蝾螈，或称火蜥蜴）, world's largest amphibian（两栖动物）, almost two meters long. They're the only large predator in these icy waters. They begin their hunt at night.
These salamanders have an exceptionally slow metabolism. Living up to 80 years they grow into giants. The fish they hunt are scarce and salamanders have poor eyesight. But sensory nodes on their head and body detect the slightest changes in water pressure. Free from competition, these giants can dine（动词，用餐，吃饭。一般用于表示正餐或大餐） alone.
Pickings are usually thin for the salamanders, but every year some of the world's high rivers are crowded by millions of visitors. The salmon（三文鱼） have arrived. This is the world's largest fresh water fish（淡水鱼） migration. Across the northern hemisphere salmon, returning from the ocean to their spawning（产卵） grounds, battle their way for hundreds of miles upstream.
