Salmon live most of their lives in the sea before swimming to the upper reaches of freshwater rivers to spawn. For this reason they are considered to be a diadromous species. In the wild salmon remain in the seas of the northern hemisphere while they are growing, and reproduce in its lakes and rivers. It is very unusual for salmon to return to the sea after spawning, as they die of exhaustion. However, Atlantic salmon can return to the sea 2 or 3 times before they die.
Young salmon, known as parr, measure from between 15 to 20 cm, and after spending approximately 2 years in freshwater migrate to the sea, where they will mature. They usually remain in the sea for around 1 to 3 years before the adult salmon return to spawn in the river where they were born.
In salmon farming salmon are raised using natural processes in tanks or enclosures which are strictly controlled. Farming salmon has not only decreased mortality rates, but has also bred salmon which is of the same quality as wild salmon by emulating the natural processes that take place in the cold Atlantic seas.
In Spain, most of the salmon that is consumed comes from aquaculture, that is to say, from salmon farms where the salmon are fertilised and incubated before being allowed to grow in the sea. Currently over 90% of the salmon that is sold has been farmed.