Salmon are river and sea fish caught or farmed in huge quantities for food.
All salmon are born in rivers and lakes far inland, then swim down river and out to sea.
Adult salmon spend anything from 6 months to 7 years in the oceans, before returning to rivers and swimming upstream to spawn (lay their eggs).
More than five salmon species, including the sockeye and the chinook, spawn in North American rivers running into the North Pacific.
Cherry salmon spawn in eastern Asian rivers, and amago salmon spawn in Japanese rivers.
Atlantic salmon spawn in rivers in northern Europe and eastern Canada.
Spawning salmon return to the same stream they were born in, up to 3,000 km inland. They are probably sensitive to the chemical and mineral make-up of streams and rivers, helping them to recognize their own stream.
To reach their spawning grounds, salmon have to swim upstream against strong currents, often leaping as high as 5 m to clear waterfalls.
When salmon reach their spawning grounds, they mate. The female lays up to 20,000 eggs.
After spawning, the weakened salmon head down river again, but few make it as far as the sea.
Salmon returning to their spawning ground make mighty leaps up raging ion cats. The journey can take months.