Trout are a diverse group of freshwater ray-finned fish, widely recognized for their importance in recreational fishing and as a food source. These fish belong to the family Salmonidae, which also includes salmon and char. The question of how many different types of trout exist is complex, largely due to varying classifications, from common names used by anglers to scientific categorizations based on genetic relationships. This diversity means that what one person calls a trout might be scientifically grouped differently.
Understanding Trout Classifications
The term “trout” serves as a common name applied to various distinct genera within the Salmonidae family. This family encompasses over 200 species across 11 genera, all of which are cold-water fish found in the Northern Hemisphere. The three primary scientific genera that contain fish commonly referred to as trout are Salmo, Oncorhynchus, and Salvelinus. These classifications group fish based on shared biological characteristics, such as their physical traits, genetic makeup, and evolutionary history.
All members of the Salmonidae family share certain features, including small cycloid scales, a single dorsal fin, and an adipose fin—a small, fleshy fin located between the dorsal fin and the tail. Many species within these genera are potamodromous, meaning they spend their entire lives in freshwater lakes and rivers, migrating upstream to spawn. However, some trout species are anadromous, spending their adult lives in saltwater before returning to freshwater to reproduce.
The True Trouts (Salmo Genus)
The Salmo genus includes the Brown Trout (Salmo trutta), often considered a “true trout.” This species is native to Europe, North Africa, and western Asia, but has been widely introduced across the globe, including North America. Brown Trout are distinguished by their brownish-yellow coloration and characteristic scattered black, red, and orange spots along their sides. Their appearance can vary significantly depending on their habitat, with river-dwelling forms often displaying more pronounced spotting compared to the more silvery, uniform appearance of sea-run individuals.
Brown Trout typically inhabit cool, clear freshwater environments such as rivers, streams, and lakes. They are opportunistic predators, feeding on aquatic insects, crustaceans, and smaller fish. Within the Salmo trutta species, there are various forms, including river trout (S. t. morpha fario), lake trout (S. t. morpha lacustris), and sea trout (S. t. morpha trutta), which is an anadromous form.
Pacific Trouts and Rainbows (Oncorhynchus Genus)
The Oncorhynchus genus includes many North American trout species, often referred to as Pacific trouts. This group features the Rainbow Trout (Oncorhynchus mykiss), which is native to the Pacific drainages of North America and parts of Asia. Rainbow Trout are identifiable by a prominent pink or reddish stripe running horizontally along their sides, accompanied by numerous small black spots on their body and fins. They can adapt to various aquatic environments, from fast-flowing rivers to large lakes, and are known for their strong fighting ability when hooked.
Within this genus, the Cutthroat Trout (Oncorhynchus clarkii) is another significant species, named for the distinctive red or orange slash marks visible under their lower jaw. Cutthroat Trout exhibit a wide range of subspecies, each adapted to specific geographic areas and often displaying unique spotting patterns. The Golden Trout (Oncorhynchus aguabonita), is also part of the Oncorhynchus genus, native to high-altitude streams and lakes in the Sierra Nevada mountains. A notable form within the Rainbow Trout species is the Steelhead, which is an anadromous, sea-run variant that spends part of its life in the ocean before returning to freshwater to spawn.
The Char Species (Salvelinus Genus)
The Salvelinus genus comprises fish commonly known as char, many of which are frequently referred to as trout, such as the Brook Trout and Lake Trout. A key distinguishing characteristic of char from true trouts (Salmo) and Pacific trouts (Oncorcorhynchus) is their spotting pattern: char typically have light spots on a darker body, whereas other trout generally have dark spots on a lighter body. This genus includes species like the Brook Trout (Salvelinus fontinalis), which despite its name, is scientifically a char. Brook Trout are native to eastern North America and are recognized by their distinctive worm-like markings (vermiculations) on their back and dorsal fin, along with red spots often surrounded by blue halos on their sides.
Lake Trout (Salvelinus namaycush) are another significant char species, native to the colder, deeper waters of North American lakes. They are the largest char species and are characterized by their pale spots on a dark green or gray body, and a deeply forked tail. Arctic Char (Salvelinus alpinus) are found in circumpolar regions, inhabiting cold, clear waters in the Arctic and sub-Arctic. These char species generally prefer colder, more pristine aquatic environments, often found in northern latitudes or at high altitudes.