Salmon, trout, whitefish, and grayling share one cold family
Salmonidae—the only living salmonoid suborder—holds eleven genera and over two hundred species of ray-finned fish. They look relatively primitive among teleosts, with rear-set pelvic fins and an adipose fin. All spawn in shallow freshwater gravel before juveniles grow in rivers, lakes, or seas along three subfamily clades.
The family takes in Atlantic and Pacific salmon, sea-run and landlocked trout, char, graylings, freshwater whitefishes, taimens and lenoks, all cold-water predators of the middle food chain. Higher estimates count about 243 species in three subfamilies: the whitefishes, including 78 species of Coregonus; the graylings, with 14 species of Thymallus; and the salmonines, including 47 species of Salmo and 51 of the char genus Salvelinus. The family is the only living member of its suborder, which together with pikes and mudminnows makes up the order Salmoniformes, first appearing late in the Cretaceous.
Salmonids keep an old-fashioned body plan among bony fishes: pelvic fins set far back, a small fleshy adipose fin near the tail, slim bodies with rounded scales, forked tails and a single row of sharp teeth. The smallest species measures only 13 centimetres. All spawn in shallow gravel in freshwater headwaters, grow up in creeks, rivers and small lakes, then move to bigger waters as adults, and many tolerate salt and head for estuaries or the sea.
Their genome carries a remarkable legacy. When the lineage split from other teleosts, no later than 88 million years ago, its ancestor doubled its entire genome, becoming tetraploid, the fourth such event in its evolutionary line. Living salmonids have been drifting back toward a normal double set: in rainbow trout about half the duplicated protein-coding genes have been lost, though microRNA sequences remain fully doubled. Improved molecular clocks narrowed earlier estimates of 25 to 100 million years for the duplication and suggest that most speciation came later rather than directly from the doubling.
The fossil record is patchy. Eosalmo driftwoodensis from Eocene lake beds in British Columbia mixes traits of all three subfamilies. After it comes a long gap until trout-like Oncorhynchus fossils about 7 million years old at Clarkia in Idaho, far inland. A Late Cretaceous genus, Sivulliusalmo, described in 2025, now predates both.
Source: Salmonidae
