Salmon

The Atlantic salmon is a large anadromous fish in the family Salmonidae, meaning it hatches and rears in freshwater rivers before migrating to the ocean to grow and mature, then returns to its natal river to spawn. Native to rivers draining into the North Atlantic in Europe and eastern North America, it undergoes dramatic physiological changes during its life cycle, shifting between freshwater and saltwater osmoregulation. Wild populations have declined significantly across much of their range due to dam construction, habitat degradation, and other pressures, leading to conservation concern in many regions, while farmed Atlantic salmon aquaculture has expanded considerably worldwide.

• Streamlined, torpedo-shaped body
• Silvery sides and white belly in ocean phase; darker, mottled coloring with red or brown blotches in spawning freshwater phase
• Small black spots scattered above the lateral line, mostly forward of the dorsal fin
• Slightly forked tail fin
• Small adipose fin between the dorsal and tail fins, a trait shared by all salmonids
• Adults typically 60-100 cm

Spawning males develop a hooked lower jaw (kype) and darker coloration, distinguishing them from silvery ocean-phase fish and from females. Juveniles in freshwater, called parr, show distinct vertical bars along the flanks that fade as they transition toward the silvery smolt stage before migrating to sea.

Atlantic salmon require clean, cold, well-oxygenated rivers with gravel beds for spawning and juvenile rearing, found in eastern North America and western Europe from Portugal north to Russia. Juveniles spend one to several years in freshwater before undergoing smoltification, a physiological transformation enabling ocean life, and migrating to the North Atlantic to feed and grow, often traveling to waters off Greenland or the Norwegian Sea. Adults return to their natal river to spawn, tolerating a wide temperature range across their life cycle but requiring cool, oxygen-rich water, generally below about 20 degrees C, for successful reproduction and juvenile survival.

Salmon exhibit natal homing, using olfactory cues to return to the specific river or stream where they hatched after one to several years at sea. Spawning females dig gravel nests called redds using their tail, deposit eggs, and are fertilized by attending males, with some individuals capable of surviving to spawn more than once. In freshwater, juveniles feed on aquatic insects and small invertebrates, while ocean-phase adults prey on fish and crustaceans, growing rapidly during their marine feeding period. Atlantic salmon are a valued sport fish throughout their range, and their migrations link marine nutrients to freshwater and terrestrial food webs, supporting a wide array of predators and scavengers.