Salmonidae

Salmonidae (, lit. "salmon-like") is a family of ray-finned fish that constitutes the only currently extant family in the order Salmoniformes (, lit. "salmon-shaped"), consisting of 11 extant genera and over 200 species collectively known as "salmonids" or "salmonoids". The family includes salmon (both Atlantic and Pacific species), trout (both ocean-going and landlocked), char, graylings, freshwater whitefishes, taimens and lenoks, all coldwater mid-level predatory fish that inhabit the subarctic and cool temperate waters of the Northern Hemisphere. The Atlantic salmon (Salmo salar), whose Latin name became that of its genus Salmo, is also the eponym of the family and order names.

Salmonids have a relatively primitive appearance among teleost fish, with the pelvic fins being placed far back, and an adipose fin towards the rear of the back. They have slender bodies with rounded scales and forked tail fins, and their mouths contain a single row of sharp teeth. Although the smallest salmonid species is just 13 cm (5.1 in) long for adults, most salmonids are much larger, with the largest reaching 2 m (6 ft 7 in).

All salmonids are migratory fish that spawn in the shallow gravel beds of freshwater headstreams, spend the growing juvenile years in rivers, creeks, small lakes and wetlands, but migrate downstream upon maturity and spend most of their adult lives at much larger waterbodies. Many salmonid species are euryhaline and migrate to the sea or brackish estuaries as soon as they approach adulthood, returning to the upper streams only to reproduce. Such sea-run life cycle is described as anadromous, and other freshwater salmonids that migrate purely between lakes and rivers are considered potamodromous. Salmonids are carnivorous predators of the middle food chain, feeding on smaller fish, crustaceans, aquatic insects and larvae, tadpoles and sometimes fish eggs (even those of their own kind), and in turn being preyed upon by larger predators. Many species of salmonids are thus considered keystone organisms important for both freshwater and terrestrial ecosystems due to the biomass transfer provided by their mass migration from oceanic to inland waterbodies.