The eggs of salmon are laid and buried in the gravel at the bottom of cold streams. There they remain for around 3 months in the UK - for longer in cold climates. When they hatch they are called "alevins" and are around 1.5 cm (¾ inch) long, feeding from the yolk sac protruding from their bellies before emerging as, first, "fry" and later becoming "parr". At this stage they reach only up to 7 cm (3") in length and develop a brown back with black spots and bars and the occasional red spot. Migration takes place, in the UK, generally in the second year (again, longer in colder climates, up to the third year). At this point they lose the coloration and become silvery, making them more appropriate for the sea. Various internal changes occur as well, to equip them for a saline environment. They return to the rivers of their birth to spawn. Those returning after one year at sea are known as "grilse" which can weigh as much as 4 kg (8 lb). It is not until they are two years old or more that they are called salmon, in which form they can reach 12 kg (25 lb) in weight. When they return to the rivers to spawn they are in their best possible condition, making them prey for fishermen. Those that survive the fishing are known as "kelts" and those that survive the whole spawning process and return to the sea are known as "mended kelts".
