A few fish, like salmon and eels, spend some of their life in both freshwater and seawater, but most freshwater fish cannot survive in the salty sea water. Some, such as trout and grayling, prefer fast-flowing streams like those flowing from chalk downland. Slow-flowing rivers and lakes are the home of tench, rudd and carp. Here, large predatory pike often lurk in the weeds. Shoals of fish feed on floating plankton, or take insects from the surface, while common bream and barbel graze on the bottom, eating insect larvae, worms and molluscs.
Sea trout are solitary hunters, preying on small fish and water creatures.
Roach are found in lakes and slow-flowing rivers. Salmon spend most of their life in the sea, but eventually swim into a river to return to the place where they were spawned. On the journey upstream they battle against strong currents and leap up waterfalls and rapids. When they reach the spawning ground, they mate. The female lays her eggs in the gravel, then male and female drift down river to die.