<P> The colouration of young Atlantic salmon does not resemble the adult stage . While they live in fresh water, they have blue and red spots . At maturity, they take on a silver - blue sheen . The easiest way of identifying them as an adult is by the black spots predominantly above the lateral line, though the caudal fin is usually unspotted . When they reproduce, males take on a slight green or red colouration . The salmon has a fusiform body, and well - developed teeth . All fins, save the adipose, are bordered with black . </P> <P> The distribution of Atlantic salmon depends on water temperature . Because of climate change, some of the species' southern populations, in Spain and other warm countries, are growing smaller and are expected to be extirpated soon . Before human influence, the natural breeding grounds of Atlantic salmon were rivers in Europe and the eastern coast of North America . When North America was settled by Europeans, eggs were brought on trains to the west coast and introduced into the rivers there . Other attempts to bring Atlantic salmon to new settlements were made; e.g. New Zealand . But since there are no suitable ocean currents on New Zealand, most of these introductions failed . There is at least one landlocked population of Atlantic salmon on New Zealand, where the fish never go out to sea . </P> <P> Young salmon spend one to four years in their natal river . When they are large enough (c. 15 centimetres (5.9 in)), they smoltify, changing camouflage from stream - adapted with large, gray spots to sea - adapted with shiny sides . They also undergo some endocrinological changes to adapt to osmotic differences between fresh water and seawater habitat . When smoltification is complete, the parr (young fish) now begin to swim with the current instead of against it . With this behavioral change, the fish are now referred to as smolt . When the smolt reach the sea, they follow sea surface currents and feed on plankton or fry from other fish species such as herring . During their time at sea, they can sense the change in the Earth magnetic field through iron in their lateral line . </P> <P> When they have had a year of good growth, they will move to the sea surface currents that transport them back to their natal river . It is a major misconception that salmon swim thousands of kilometers at sea; instead they surf through sea surface currents . When they reach their natal river they find it by smell; only 5% of Atlantic salmon go up the wrong river . Thus, the habitat of Atlantic salmon is the river where they are born and the sea surface currents that are connected to that river in a circular path . </P>

Where do atlantic salmon go in the ocean