Brown trout (Salmo trutta) are a highly sought-after species by anglers globally, known for their adaptability and widespread distribution. Originating from Europe, Western Asia, and Northern Africa, they have been introduced to various parts of the world, making them one of the most widely distributed non-native cold-water fish. This species is celebrated for its striking coloration, which can range from silver to olive, gold, and even reddish hues, often adorned with distinct dark spots. Their resilience and ability to thrive in diverse aquatic environments contribute to their popularity among recreational fishers.
Average Brown Trout Size
The typical size of an adult brown trout varies significantly depending on its habitat. In stream environments, brown trout commonly reach lengths of 15 to 22 inches and weigh between 1 and 5 pounds. A brown trout exceeding 20 inches is generally considered a trophy catch for anglers.
Lake-dwelling brown trout, also known as adfluvial brown trout, tend to grow larger on average. This is partly due to the reduced energy expenditure for swimming against currents to find food. In these environments, brown trout can reach up to 39 inches in length and weigh between 1 and 9.5 pounds, with some individuals potentially exceeding 20 pounds.
Exceptional and Record Sizes
Brown trout can achieve impressive sizes, with the current all-tackle world record standing at 44 pounds, 5 ounces. This record-breaking fish was caught by Seumas Petrie in New Zealand’s Ohau Canal on October 27, 2020. It measured 38.58 inches in length with a 34-inch girth.
Before this, the world record was held by a 42-pound, 1-ounce brown trout, also caught in the same New Zealand canal in 2013 by Otwin Kandolf. The United States record for brown trout is 41 pounds, 8 ounces, caught by Roger Hellen from Lake Michigan in Wisconsin. Another notable US catch was a 41-pound, 7-ounce brown trout from Michigan’s Manistee River in 2009, caught by Tom Healy. Arkansas also previously held a world record with a 40-pound, 4-ounce brown trout caught in the Little Red River in 1992.
What Influences Brown Trout Size
Several biological and environmental factors significantly influence how large a brown trout can grow:
Food availability and quality. Brown trout are opportunistic predators; juveniles primarily consume aquatic insects, while larger fish often transition to a diet mainly consisting of other fish, crayfish, and fish eggs. This shift to a piscivorous diet can dramatically increase their growth rates. Abundant prey, particularly larger, energy-dense items, allows for greater growth potential.
Genetics. Different “strains” or subtypes of brown trout possess slight genetic variations that affect growth potential, spawning times, and diet preferences.
Water quality and temperature. Brown trout prefer well-oxygenated water, with optimal temperatures ranging from 50 to 60 degrees Fahrenheit. Higher temperatures can negatively impact growth and survival if food intake does not compensate for increased metabolism.
Habitat quality and available space. Brown trout prefer areas with cover, such as undercut banks and deep pools. Larger stream sizes, including greater width and depth, are associated with higher densities of older, larger juvenile brown trout.
Age and lifespan. Older fish generally grow larger, with brown trout typically living 4 to 6 years, but capable of living over 10 years in certain environments.
Fishing pressure. Selective harvesting can influence the size structure of a population by impacting the prevalence of larger, older fish.
Where Large Brown Trout Are Found
Exceptionally large brown trout are found in specific geographic locations and water bodies that provide optimal conditions for their growth. New Zealand’s hydro canals, particularly the Ohau Canal, are renowned for producing world-record-sized brown trout, largely attributed to abundant food sources, including pellets from nearby salmon farms.
In the United States, several regions are famous for their trophy brown trout. The White River in Arkansas, especially below Bull Shoals Dam, is known for consistently producing large brown trout. Other notable locations include the Colorado River and Gunnison River in Colorado, the Green River in Utah (particularly the C Section below Flaming Gorge Dam), and Lake Ontario tributaries. The North Platte River in Wyoming, particularly around Casper, and the Missouri River in Montana are also recognized for their populations of large brown trout. The Rio Grande River in Tierra del Fuego, Argentina, is globally recognized for its sea-run brown trout, where fish exceeding 20 pounds are common, and 30-pounders are caught annually.