Trout are a diverse group of freshwater fish belonging to the salmon family, Salmonidae. They are typically found in cool, clear waters across North America, Europe, and Asia. Their size can vary considerably depending on the specific species and the environment they inhabit.
Common Trout Species and Their Sizes
Rainbow trout (Oncorhynchus mykiss) are widely distributed and known for their vibrant coloration. Adult rainbow trout commonly average between 20 to 23 inches in length, weighing 4 to 8 pounds. However, under optimal conditions, they can grow significantly larger, with the current world record rainbow trout weighing 48 pounds and measuring 42 inches long.
Brown trout (Salmo trutta), native to Europe and Asia, have been introduced globally and are prized for their elusive nature. Average adult brown trout range from 7 to 14 inches in length and weigh 1 to 9.5 pounds. The all-tackle world record for a brown trout stands at an impressive 44 pounds, 5 ounces, caught in New Zealand.
Brook trout (Salvelinus fontinalis), a type of char native to Eastern North America, are often found in smaller streams. In streams, their typical size is 6 to 15 inches, weighing 1 to 5 pounds, though they can reach 10 to 26 inches and 0.6 to 6.6 pounds in larger waters. The world record brook trout, caught in Canada, weighed 14 pounds, 8 ounces and was 31.5 inches long.
Lake trout (Salvelinus namaycush) are the largest char species and inhabit deep, cold freshwater lakes in North America. These fish typically measure between 20 and 36 inches in length and weigh 4 to 22 pounds. The official world record lake trout is a 72-pound specimen, caught in Canada’s Great Bear Lake.
Cutthroat trout (Oncorhynchus clarkii) are identifiable by the distinctive red or orange marks under their lower jaw. Their average size varies widely, from 8 to 22 inches in length and 0.5 to 8 pounds in weight, with stream-resident fish being much smaller than those in large lakes. The largest cutthroat trout on record weighed 41 pounds and was 39 inches long, caught in Pyramid Lake, Nevada.
Key Factors Influencing Trout Size
A trout’s age is a primary determinant of its size; older fish generally grow larger. Growth rate is also influenced by the availability and quality of food sources. Abundant and nutritious prey, such as insects, smaller fish, or fish farm pellets, can lead to accelerated growth and larger size.
Water quality and temperature play a role in trout development; optimal conditions support healthy growth. Trout thrive in cold, clean, and well-oxygenated water, while extreme temperatures or poor water quality can impede growth and reduce potential size. Habitat size and type also affect how large trout can become. Larger bodies of water, like lakes or diverse river systems, provide more space and resources, enabling fish to grow larger than those in smaller, more confined streams.
Genetic factors also contribute to growth potential, with certain individual fish or strains naturally predisposed to attain larger sizes. For example, some Lahontan cutthroat and triploid rainbow trout strains are known for exceptional growth. Fishing pressure in a given area can also impact the average size of trout. Heavily fished waters might have fewer older, larger individuals due to increased harvest rates.
Measuring Trout and Record Catches
Trout size is typically determined by total length, measured from the snout to the tail, or by weight using a scale. Girth, the circumference around the thickest part, is also important for estimating weight when a scale is unavailable. Formulas can use length and girth to estimate a fish’s weight.
Official fishing records, like those by the International Game Fish Association (IGFA), establish record catches. To qualify, fish must be weighed on certified scales, and the catch often requires photographs, witnesses, and adherence to angling rules. Fish from hatchery waters or commercially stocked ponds typically do not qualify for official records.
These strict requirements ensure the legitimacy of record-breaking catches, representing the maximum potential size for a species. For instance, Sean Konrad’s 48-pound rainbow trout from Lake Diefenbaker and Seumas Petrie’s 44-pound, 5-ounce brown trout from New Zealand exemplify the upper size limits for these species. The 14-pound, 8-ounce brook trout by Dr. J.W. Cook and Lloyd Bull’s 72-pound lake trout also stand as benchmarks for their species.