Trout are a diverse group of fish, but precisely counting their distinct species is complex. This is due to ongoing scientific classification efforts and the broad use of “trout” as a common name, which encompasses various species across different scientific classifications.
Defining What a Trout Is
The term “trout” serves as a common name rather than a single scientific classification. It generally refers to various species of ray-finned fish that belong to the family Salmonidae, specifically within the subfamily Salmoninae. These fish primarily fall under three genera: Salmo, Oncorhynchus, and Salvelinus. Trout typically exhibit streamlined bodies and possess an adipose fin. Most trout live in freshwater environments, though some species are anadromous, meaning they migrate between freshwater and saltwater.
While closely related within the Salmonidae family, trout are distinct from other salmonids like Pacific salmon, grayling, and whitefish. Species commonly called “trout” from the Salvelinus genus are scientifically classified as char. Char can be distinguished by their characteristic light-colored spots on a darker body, contrasting with the dark spots found on the lighter bodies of species in the Salmo and Oncorhynchus genera.
The Dynamic Number of Trout Species
Determining a definitive number of trout species is not straightforward, as ongoing scientific research and reclassification continuously update our understanding. Genetic analysis, for instance, can reveal new species or lead to reclassification. The Brown Trout (Salmo trutta) shows significant genetic variation, leading to attempts to classify it into numerous separate species due to its adaptability. Consequently, the number of recognized species generally falls within a range of approximately 20 to 30, expanding considerably when considering subspecies and regional variations.
The complexity is further compounded by hybridization, where different trout species interbreed. This can occur naturally when species share spawning grounds, or through human intervention in hatcheries. Examples include the Tiger Trout, a sterile hybrid resulting from a cross between a Brown Trout and a Brook Trout. Another hybrid, the Splake, is a cross between a Lake Trout and a Brook Trout, which can be fertile. The Cutbow, a hybrid of a Cutthroat Trout and a Rainbow Trout, is also known to be fertile and can occur where their spawning seasons overlap. Such interbreeding and ongoing genetic studies mean that different scientific bodies or regions may maintain slightly varying counts of recognized trout species.
Exploring Key Trout Genera
The diversity within the trout group is best understood by examining the three primary genera that encompass most species commonly referred to as trout. These genera include Salmo, Oncorhynchus, and Salvelinus, each with distinct characteristics and geographic distributions.
The genus Salmo predominantly includes trout native to the Atlantic region. The Brown Trout (Salmo trutta) is a notable member, with its native range spanning across Europe, North Africa, and parts of Western Asia, particularly around the Black Sea basin. This species has been widely introduced globally, establishing populations in many non-native waters. Sea trout, which are anadromous forms of Brown Trout, exemplify the migratory tendencies found within this genus.
The Oncorhynchus genus consists of Pacific trout and Pacific salmon, originating from the North Pacific basin. Prominent trout species within this group include the Rainbow Trout (Oncorhynchus mykiss), the Cutthroat Trout (Oncorhynchus clarkii), and the Golden Trout (Oncorhynchus aguabonita). Their native distribution covers Western North America and Eastern Asia. Many Oncorhynchus species exhibit anadromous behavior, with the most recognized example being the Steelhead, which is a sea-run form of the Rainbow Trout.
The Salvelinus genus comprises fish scientifically known as char, though many are commonly called trout. These include the Brook Trout (Salvelinus fontinalis), Lake Trout (Salvelinus namaycush), Dolly Varden (Salvelinus malma), and Arctic Char (Salvelinus alpinus). They typically prefer colder, often pristine, water environments. This genus has a northern circumpolar distribution, with the Arctic Char being found further north than any other freshwater fish.