Salmon begin life as eggs on a pebbly riverbed, hidden among reeds in the slow-moving upper reaches of a river. After five to six months, the eggs hatch into 'fry'. For approximately the next four years, these baby salmon will live in a lower, faster-flowing waters of the river. During this time they measure between three and eight centimitres in length.

Salmon begin life as eggs on a pebbly riverbed, hidden among reeds in the slow-moving upper reaches of a river. After five to six months, the eggs hatch into 'fry'. For approximately the next four years, these baby salmon will live in a lower, faster-flowing waters of the river. During this time they measure between three and eight centimitres in length. By the time salmon reach twelve to fifteen centimitres, they are termed 'smolt', and at this time they migrate further downriver into the open sea. After five years at sea the salmon will have grown to adult size, which is between seventy and seventy-six centimetres. They then begin swimming back to their birthplace, where they will lay their legs, and the cycle starts anew. In summary, the salmon passes through three distinct physical stages as it grows to maturity. Each of these stages takes place in a very different aquatic location. It is noteworthy that the first 2 stages of this fish's life occur in a freshwater environment, while the third stage is lived in saltwater.