Trout
Carnivorous freshwater fish of the genera Oncorhynchus, Salmo, and Salvelinus.
Trout is a generic common name for numerous species of carnivorous freshwater fishes belonging to the genera Oncorhynchus, Salmo, and Salvelinus, all members of the subfamily Salmoninae in the family Salmonidae. Trout are closely related to salmon and have similar migratory life cycles, with most being potamodromous, spending their entire lives in freshwater, while some anadromous species, such as steelhead and sea trout, spend up to three years at sea before returning to freshwater to spawn. Trout are classified as oily fish, have been important food fish for humans, and serve as keystone species across aquatic and terrestrial ecosystems.
- Scientific classification
- Kingdom: Animalia, Phylum: Chordata, Class: Actinopterygii, Order: Salmoniformes, Family: Salmonidae, Subfamily: Salmoninae
- Genera
- Oncorhynchus, Salmo, Salvelinus
- Common habitats
- Cool (50–60 °F or 10–16 °C), clear streams, wetlands, and lakes
- Natural distribution
- North America, northern Asia, Europe
- Introduced regions
- Australia, New Zealand, Himalayan Region of India, Nepal, Bhutan, Pakistan, Tian Shan mountains of Kyrgyzstan
- Diet
- Other fish, soft-bodied aquatic invertebrates, zooplankton
- Lifespan
- Rainbow trout average maximum seven years; lake trout can live many decades
Lore & Background
Trout are mid-level predators that prey upon smaller aquatic animals including crustaceans, insects, worms, baitfish, and tadpoles. They are also important staple prey for many animals, including brown bears, otters, raccoons, birds of prey, gulls, cormorants, kingfishers, and other large aquatic predators. Discarded remains of trout provide nutrients for scavengers, detrivores, and riparian flora, making them keystone species. Trout that live in different environments can have dramatically different colorations and patterns, which form as camouflage and change as the fish moves to different habitats. Trout about to breed have extremely intense coloration and can look like an entirely different fish outside of spawning season. Trout have fins entirely without spines, a small adipose fin along the back near the tail, and a swim bladder connected to the esophagus, a condition known as physostome, though they do not use it for oxygen uptake.
Reader's Guide
Trout hold significance as both a food fish for humans and a keystone species in aquatic and terrestrial ecosystems. As mid-level predators, they regulate populations of smaller aquatic animals and in turn support a wide range of predators, from brown bears to birds of prey. Their migratory life cycles, including potamodromous and anadromous forms, connect freshwater and marine environments. The introduction of trout species, such as brown trout from England and rainbow trout from California, to regions like Australia and New Zealand in the 19th century by amateur fishing enthusiasts has had lasting ecological impacts, displacing and endangering several upland native fish species. Despite this, trout remain extremely popular gamefish, with millions released annually from hatcheries. The taxonomy of trout is complex, with many distinct populations showing no significant genetic differences, leading ichthyologists to recognize a smaller number of distinct species than physical characteristics suggest. For example, brook trout, aurora trout, and the extinct silver trout are genetically one species, Salvelinus fontinalis.
Did You Know?
- The word trout is also used for some non-salmonid fish, such as the spotted seatrout (Cynoscion nebulosus), which is actually a croaker.
- Brook trout and three other extant species of North American trout are actually char (or charr), closely related to trout and salmon.
- Lake trout can live many decades and grow to more than 30 kilograms (66 lb), while rainbow trout have an average maximum lifespan of seven years.
- The rainbow trout of New Zealand still show the steelhead tendency to run up rivers in winter to spawn.
Frequently Asked Questions
Who is Trout?
Trout is not a single species but a broad common name covering many carnivorous freshwater fish spread across three genera—Oncorhynchus, Salmo, and Salvelinus—all nested within the Salmoninae subfamily. They are close relatives of salmon and share broadly similar life-history patterns.
What are Trout's powers/role?
In their home ecosystems, trout function as keystone predators, preying on smaller fish and soft-bodied aquatic invertebrates to keep stream and lake food webs in balance. Their sensitivity to water conditions also makes them a living indicator of habitat health, since they demand cool, clear, well-oxygenated water.
How does Trout's story end?
Most trout are potamodromous, meaning they live, grow, spawn, and die entirely within freshwater systems. A handful of anadromous lines, such as steelhead and sea trout, spend up to three years in the ocean before returning to their natal rivers to reproduce and complete their life cycle.
Why is Trout important?
Trout have been a valued food fish for human communities for centuries and are classified as oily fish, giving them a rich nutritional profile. Ecologically, their position as apex freshwater predators makes them keystone species whose loss would ripple through entire aquatic food webs.
Where can you find Trout?
Natively, trout occupy cool (roughly 10–16 °C), clear streams, lakes, and wetlands across North America, northern Asia, and Europe. They have also been introduced to waters in Australia, New Zealand, parts of South Asia, and the Tian Shan mountain range of Kyrgyzstan.
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