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Trout and Salmon · Salmonidae

Brown Trout

Salmo trutta

A European fish that arrived in crates in the 1880s, brown trout now hold the warm lower ends of American trout rivers — and are removed from three national parks.

Brown Trout (Salmo trutta)
Brown Trout. Raver, Duane, Public domain. Source.

Recognizing the fish

Brown trout are heavy-shouldered, blunt-headed trout with a squared or barely notched tail and a body ground color that runs from buttery yellow-gold through olive to near-bronze. The defining mark is the spotting: dark spots on the back and flanks are mixed with rusty red or orange spots, and many of those spots sit inside pale halos. Spotting stops at the lateral line region in many fish and rarely extends onto the tail, which separates them cleanly from rainbow trout, whose tails are heavily peppered.

Coloration is plastic. Fish from tannic freestone rivers run dark and heavily marked; fish from limestone spring creeks are pale and silvery; sea-run and lake-run fish are chrome with faint X-shaped marks and lose the red spotting almost entirely. Large males develop a pronounced kype in autumn. Because the same species can look this different from one river to the next, the reliable characters are structural: the deep caudal peduncle, the small adipose fin often edged in orange, and the halo-ringed spots.

How brown trout got to North America

Brown trout are not native to any part of the Western Hemisphere. Their arrival is one of the best-documented introductions in American fisheries history, and also one of the most garbled in retelling.

The first eggs came from Germany in 1883, secured through Fred Mather of the US Fish Commission and distributed from the Commission’s hatchery at Cold Spring Harbor, New York. The US Geological Survey’s Nonindigenous Aquatic Species program records that “the Brown Trout was first imported to the United States in 1883 from Germany and stocked in the Pere Marquette River, Michigan, by the U.S. Fish Commission.” The resulting fry went into the water in 1884, into a tributary of Michigan’s Pere Marquette. Sources differ on which date to call the introduction: agencies that date it by the egg shipment say 1883, and the Michigan Department of Natural Resources follows that convention, stating that brown trout “were introduced to Michigan in 1883 — one of the first states to import them into North America.” Accounts that date it by the first fish in the river say 1884. Both are defensible; they are measuring different events.

The German shipment is conventionally associated with Lucius von Behr, then president of the German Fisheries Society, and “von Behr trout” survives as a strain name for the Continental stock. The elaborate version of that story — a named steamship, a named crossing, a dramatic rescue of the eggs — could not be traced to any primary source. Treat von Behr as a strain name and a plausible attribution of the donor, not as a documented voyage narrative.

The Loch Leven strain arrived later, and separately

The second founding stock is where most published accounts go wrong. Loch Leven trout — the Scottish lake strain, historically treated as a distinct form and still used as a strain designation in American hatcheries — did not come over with the German eggs in 1883. They came a year later, from a different country, through a different hatchery.

The eggs were taken at the Howietoun hatchery near Stirling, Scotland, on 12 November 1884, and reached Cold Spring Harbor on 2 January 1885. The record is Charles W. Smiley’s article “Loch Leven Trout introduced in the United States,” at page 28 of volume 7 of the Bulletin of the United States Fish Commission (1887). Online summaries that fold Loch Leven into the 1883 German shipment, or that give 1883 as the Loch Leven date, are repeating an error. The two strains were imported separately, roughly fourteen months apart, and were interbred in American hatcheries soon afterward. Modern US brown trout populations are mixtures; the strain names attached to hatchery lots describe ancestry loosely at best.

Where they live now

Brown trout are established in cold and cool rivers across the northern tier of the country, throughout the Appalachians and the Ozarks, across the Rockies and the interior West, and in Great Lakes tributaries where lake-run fish move up to spawn. The US Fish and Wildlife Service maintains a species profile for them despite their non-native status, reflecting how thoroughly embedded they are in American fisheries management.

Their distribution in any given watershed tends to be the mirror image of the native char. Where brook trout occupy the cold headwaters, brown trout own the middle and lower river. In the West, brown trout hold the mainstem while cutthroat retreat upstream. Wisconsin’s classification of trout water — Class 1 streams with self-sustaining wild reproduction, Class 2 with partial reproduction, Class 3 marginal — maps closely onto where brown trout reproduce naturally versus where they persist only through stocking.

Water temperature

Temperature is the single most useful number for predicting brown trout behavior in a river. Growth and active feeding concentrate between roughly 54 and 66 °F. Below about 40 °F metabolism slows and fish hold low and feed sparingly. Above about 68 °F, oxygen demand climbs while dissolved oxygen falls, and fish begin to seek out cold seeps, spring inflows and tributary mouths.

The most defensible upper limits come from field data rather than laboratory tanks. Wehrly, Wang and Mitro’s field-based estimates of thermal tolerance for trout in Michigan and Wisconsin streams found no difference between brook and brown trout in upper thermal tolerance, and placed the seven-day limits at a maximum daily mean of 23.3 °C (73.9 °F) and a maximum daily maximum of 25.4 °C (77.7 °F). Critically, those limits are duration-dependent: tolerance falls steeply between one and fourteen days of exposure, then declines more gradually over longer periods. A river that touches 75 °F for two hours on one afternoon is a different proposition from a river that averages 73 °F for a week.

Relative to other salmonids, brown trout are the warm-water specialists of the group. Michigan’s fisheries agency attributes their spread through that state’s rivers to being “more tolerant of warmer water temperatures than other trout species.” On rivers where a live temperature reading is available, the practical threshold to watch is the daily maximum crossing into the low 70s and, more importantly, whether it stays there overnight.

Eyes built for low light

The best-supported explanation for brown trout behavior is optical. Rader, Belish, Young and Rothlisberger compared dark-adapted vision across four trout species in “The scotopic visual sensitivity of four species of trout: a comparative study” (Western North American Naturalist 67:524–537, 2007, with US Forest Service involvement). Brown trout and brook trout could resolve prey at roughly twice the low-light sensitivity of rainbow and cutthroat trout — that is, they can still see and feed at light levels where the other two species effectively cannot.

This single result carries an unusual amount of explanatory weight. It accounts for the strongly nocturnal and crepuscular feeding of larger brown trout, and for the observation that the biggest fish in a river are often functionally invisible during daylight. It also supplies a mechanism for competitive displacement. If two species share a river and one of them can forage through the night while the other cannot, the difference compounds across a season. The authors proposed exactly this as a mechanism by which brown trout exclude native cutthroat trout, and it complements the field record: USGS notes that brown trout “have commonly replaced Cutthroat Trout (O. clarkii) in large rivers,” that “adult Brown Trout displaced adult native Brook Trout from the best habitats in a Michigan stream,” and that predicted brook trout occurrence is lower where brown trout are present.

Feeding and growth

Juvenile brown trout eat drifting invertebrates — mayfly, caddis and midge larvae, terrestrials that fall in from the bank. Somewhere past roughly 12 to 14 inches, the diet shifts. Large brown trout in rivers become substantially piscivorous, taking sculpin, dace, juvenile trout and crayfish, and this shift is what produces the disproportionately large individuals that rivers with good forage bases yield. The switch is also why brown trout populations often show a bimodal size structure: many small drift-feeders and a few very large predators, with comparatively few fish in between.

Growth rate tracks temperature and food. Fish in cold, infertile freestone headwaters may take five years to reach 12 inches. Fish in fertile tailwaters, where a bottom-release dam holds summer temperatures in the fifties and sixties and delivers a constant invertebrate supply, can exceed 20 inches in three or four years. The same species produces both outcomes; the river does the work.

Spawning

Brown trout spawn in autumn, in contrast to spring-spawning rainbow trout. Timing runs from September at high latitude and elevation through December in southern and low-elevation rivers, with the trigger being falling water temperature through roughly the mid-40s to low 50s °F, often reinforced by shortening day length and autumn flow increases. In Michigan, the state agency reports spawning “in tributary streams in September and October,” in “shallow, gravelly or rocky areas.”

Females cut redds in clean gravel at the tails of pools and in riffle margins, preferring places with downwelling flow through the substrate that will keep eggs oxygenated. Eggs incubate through winter and hatch in late winter or early spring, with alevins remaining in the gravel until yolk absorption. Fine sediment is the dominant threat to this life stage — silt infilling the gravel suffocates eggs before they hatch — which is why land use in the upper watershed shows up in trout numbers two years later.

Whirling disease

Whirling disease is caused by Myxobolus cerebralis, a parasite that invades head and spinal cartilage in young trout, producing skeletal deformity, erratic swimming and, in heavy infections, high mortality. The USGS Fish Health Program notes it is “thought to have been introduced from Europe,” was first detected in the US in 1958, and now occurs in more than twenty states.

Brown trout are comparatively resistant to it, and the reason is evolutionary: the parasite originated in Europe, where brown trout are native and where the two have a long shared history. Rainbow trout, cutthroat trout and bull trout — all New World species with no such history — are far more vulnerable, and rainbow trout collapses in Rocky Mountain rivers during the 1990s were the disease’s most visible effect. The accurate framing is resistance rather than “reservoir host”: brown trout are infected and can carry the parasite, but they mount a far more effective response to it than the native species they share water with. The comparative work is summarized in Hedrick and colleagues’ comparative susceptibility study of rainbow and brown trout in Diseases of Aquatic Organisms.

Prized fishery and removal target at the same time

Brown trout occupy an awkward position in American river management. They support some of the most valued river fisheries in the country and they are simultaneously the target of removal programs in national parks charged with restoring native fish.

In Grand Canyon National Park, the Native Fish Ecology and Conservation program removes “invasive trout and other invasive fishes in an effort to minimize threats of predation and restore native fishes and habitat in larger perennial tributaries,” in a river system whose humpback chub population is the largest remaining anywhere. In Great Smoky Mountains National Park, non-native trout have displaced native brook trout from a large share of their historical range, and restoration work there is built around reclaiming headwater reaches. In Yellowstone, the park’s westslope cutthroat program records that “nonnative brook and brown trout” contributed to native cutthroat decline by the 1930s, and describes removals in East Fork Specimen Creek and the upper Gibbon River ahead of restocking with genetically pure cutthroat. The park’s broader fisheries mission is explicitly framed around preserving native species. Removal methods and effects have been studied directly, including work on how brown trout removal affects survival and movement of remaining fish.

None of this is a contradiction so much as a matter of scale. On a tailwater built by a dam, where the native assemblage is already gone, brown trout are the fishery. On a headwater tributary that still holds a genetically intact native population, they are the problem. Both statements are true of the same species in the same state.

Habitat and behavior in rivers

Brown trout are structure-oriented in a way that other trout are not. They sit tight to undercut banks, log jams, boulder shadows and the deep slots along outside bends, and they defend those positions. Larger fish claim the best lies — the ones with the most food delivered for the least effort — and hold them across seasons. The pattern is consistent enough that a river’s productive water can be read from its structure alone.

Their nocturnal habit shapes everything downstream of it. Large brown trout move out of deep cover after dusk to hunt shallow flats and tailouts, and return before full light. The visual sensitivity data explains why this works for them and not for the rainbow trout in the same pool. In midsummer, thermal refuge overrides everything: fish concentrate at spring seeps, cold tributary confluences and dam release plumes, and abandon the reaches between them. A live water temperature reading, and the location of the nearest cold input, describe brown trout distribution in a July river better than any other pair of variables.

Where to catch it

419 waterways on GuidedFloats list brown trout, across 40 states. Each page carries live gauge readings, access notes, and the guides who fish it.

Arizona 13

Arkansas 5

California 12

Colorado 20

Connecticut 9

Delaware 3

Georgia 6

Idaho 13

Iowa 5

Kentucky 1

Maine 8

Maryland 12

Massachusetts 8

Michigan 9

Minnesota 5

Missouri 9

Montana 20

Nebraska 6

Nevada 13

New Hampshire 20

New Jersey 4

New Mexico 12

New York 20

North Carolina 14

Ohio 3

Oklahoma 2

Oregon 4

Pennsylvania 32

Rhode Island 11

South Carolina 2

South Dakota 15

Tennessee 4

Texas 1

Utah 16

Vermont 18

Virginia 12

Washington 1

West Virginia 16

Wisconsin 16

Wyoming 19

References

  1. Brown Trout (Salmo trutta) — Nonindigenous Aquatic Species factsheet — U.S. Geological Survey
  2. Brown Trout (Salmo trutta) species profile — U.S. Fish and Wildlife Service
  3. Brown Trout — Michigan Species — Michigan Department of Natural Resources
  4. The scotopic visual sensitivity of four species of trout: a comparative study (Rader, Belish, Young & Rothlisberger, Western North American Naturalist 67:524–537, 2007) — Brigham Young University ScholarsArchive / USDA Forest Service
  5. Bulletin of the United States Fish Commission, Volume 7 (1887) — includes C. W. Smiley, 'Loch Leven Trout introduced in the United States', p. 28 — United States Fish Commission
  6. Field-Based Estimates of Thermal Tolerance Limits for Trout: Incorporating Exposure Time and Temperature Fluctuation (Wehrly, Wang & Mitro, TAFS 136:365–374, 2007) — Transactions of the American Fisheries Society
  7. Whirling Disease — Fish Health Program — U.S. Geological Survey
  8. Comparative susceptibility of rainbow trout Oncorhynchus mykiss and brown trout Salmo trutta to Myxobolus cerebralis (Hedrick et al., Diseases of Aquatic Organisms 37:173–183, 1999) — Diseases of Aquatic Organisms
  9. Fish — Grand Canyon National Park — National Park Service
  10. Fish — Great Smoky Mountains National Park — National Park Service
  11. Westslope Cutthroat Trout — Yellowstone National Park — National Park Service
  12. Fish — Yellowstone National Park — National Park Service
  13. Brown Trout Removal Effects on Survival and Movement (Fetherman et al., TAFS, 2015) — Transactions of the American Fisheries Society
  14. Wisconsin Trout Stream Classification — Wisconsin Department of Natural Resources
  15. Salmo trutta — IUCN Red List assessment — International Union for Conservation of Nature
  16. IGFA World Records database — International Game Fish Association