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Brook trout: the American that has lived in Europe's cold streams since 1884

In 1884, according to German Wikipedia, it came to Europe from North America — and ever since it has lived in cold streams and mountain lakes where it never belonged. In English it's called a trout, but it isn't one: it's a char. This article is about the brook trout, *Salvelinus fontinalis* (also brook charr, speckled trout and brookie) — German Bachsaibling, French omble de fontaine (also saumon de fontaine and truite mouchetée), Italian salmerino di fontana, Spanish trucha de arroyo, Portuguese truta-das-fontes (GBIF), Dutch bronforel, Danish kildeørred (GBIF), Swedish bäckröding, Norwegian bekkerøye, Finnish puronieriä, Russian американская палия, Croatian and Slovenian potočna zlatovčica, Albanian trofta e përrenjve (GBIF), Japanese カワマス and Arabic لفاشة الينابيع (Wikidata); for Greek we found no name of its own in either Wikidata or GBIF, and we could not confirm that the Turkish form listed by GBIF is in common use. It's a predator of cold, clear water. Here's how to recognise it, what it eats, when it spawns — and why it's a stranger here.

A char called trout

It was described by the naturalist Samuel Latham Mitchill in 1814 as *Salmo fontinalis* (English Wikipedia) — so at first in the genus of salmon and trout. Later it was moved to the chars, in the genus *Salvelinus*, which also includes the Arctic char and the lake trout. According to English Wikipedia, the species name *fontinalis* is Latin and means “of a spring” — and indeed FishBase describes its habitat as clear, cool, well-oxygenated streams, small to medium rivers and lakes. That it's still called trout in English is a legacy of the time before the reclassification: the name stayed, the genus changed.

How to recognise it

FishBase names a combination that identifies it reliably: dark green marbling on the back and on the dorsal fin — and red spots with blue halos on the flanks. The colouring varies but is usually green to brownish, with paler wormlike markings on the back that extend into the dorsal fin and sometimes into the tail fin; the flanks carry numerous pale spots and a few red ones. The second reliable feature is on the lower fins: according to FishBase, the anal, pelvic and pectoral fins have a white leading edge, followed by a dark stripe, with the rest reddish. The tail fin is almost straight or only slightly forked. At spawning time the lower flanks and fins turn red; fish that migrate to the sea are dark green above, silvery on the sides and carry only pale pink spots.

  • Size: according to FishBase at most 86 cm (standard length), commonly 26.4 cm; in Europe, according to German Wikipedia, the average size in the wild is rarely over 35 cm.
  • Weight: the heaviest published weight, according to FishBase, is 8.0 kg; in Europe, according to German Wikipedia, it usually doesn't exceed 1 kg.
  • Age: according to FishBase up to 24 years — but according to English Wikipedia most fish only live 3 to 4 years.

Where it lives

According to FishBase, its home is eastern North America: almost all of eastern Canada from Newfoundland and Labrador to the western side of Hudson Bay, south through the drainages of the Atlantic, the Great Lakes and the Mississippi to Minnesota, and along the Appalachians to northern Georgia. From there, according to FishBase, it has been widely introduced — within North America and into the temperate zones of other continents. According to FishBase it lives in a temperature range of 0 to 25 °C; English Wikipedia gives 1 to 22 °C as typical and describes warm summers with low water as stressful, especially for large fish. Its tolerance of acidic water is striking: according to English Wikipedia it typically lives at a pH of 5.0 to 7.5, at extremes 3.5 to 9.8 — and according to German Wikipedia it copes with low pH better than the native brown trout. Besides running water, according to German Wikipedia it also colonises still waters such as mountain lakes.

What it eats

According to FishBase it eats almost anything that falls into a stream or lives in it: worms, leeches, crustaceans, insects — including midges, caddisflies, blackflies, mayflies, stoneflies and dragonflies —, molluscs, fish and amphibians, and even small mammals. English Wikipedia names voles as an example and adds that it occasionally eats young of its own species. According to German Wikipedia, terrestrial insects such as grasshoppers are important in summer, and larger specimens hunt fish, including their own kind. FishBase places it at trophic level 3.3.

Spawning in autumn, in spring water

According to English Wikipedia, the brook trout spawns in autumn. FishBase describes the courtship: the male tries to drive a female towards suitable spawning gravel; the female chooses the spot and digs a redd, while the male darts back and forth beside her, quivers and brushes her with his fins — but spends most of his time chasing off other males. According to English Wikipedia, the female digs the redd where groundwater seeps up through the gravel; the eggs take their oxygen from the water flowing through the gravel. A female lays up to 5,000 eggs; they lie in the gravel over winter and hatch after 4 to 6 weeks. FishBase rates its resilience as medium: a population needs 1.4 to 4.4 years to double.

Salters and coasters: the ones that move on

Not every brook trout stays in the stream. Some fish, called salters in North America, move to the sea in spring, according to FishBase, when the stream water warms up — but never go more than a few kilometres from the river mouth and stay up to three months. According to English Wikipedia they return in late summer or autumn to spawn. Lake Superior is home to the coasters: populations that, according to English Wikipedia, live in the lake, live longer, are more predatory and run up the tributaries to spawn.

Hybrids: tiger trout, splake, Elsässer Saibling

  • Tiger trout: a cross between brook trout and brown trout — sterile according to German and English Wikipedia; English Wikipedia calls it almost always infertile and says it is used for stocking because of its fast growth.
  • Splake: a cross between brook trout and lake trout — fertile according to English Wikipedia, but with very limited natural reproduction.
  • Elsässer Saibling (German name, literally “Alsatian char”): according to German Wikipedia a cross between brook trout and Arctic char.

A stranger in the stream

In its home range it's a fish of springs — in Europe it's an introduced species. FishBase notes that several countries report adverse ecological impacts after its introduction and lists it as a potential pest. According to English Wikipedia, introduced brook trout can outcompete, eat and hybridise with native species; in the northern Rocky Mountains it contributes to the decline of the native cutthroat trout, and in Europe it has impaired the growth of the native brown trout. German Wikipedia therefore advises against stocking this species, so as not to disturb existing ecosystems. Globally, according to the IUCN, it is not threatened (Least Concern; assessed on 1 August 2021, according to FishBase), even though native populations have declined since the 19th century, according to English Wikipedia. Its uses are varied: FishBase lists it as a game fish, in commercial aquaculture and as an experimental animal, and German Wikipedia calls it a popular farmed species. Closed seasons, minimum sizes and bag limits differ by country and by water — check them yourself before you fish, with the water bailiff, the club, the fisheries authority or your guide.

Four contradictions, left standing

  • How heavy does it get? FishBase: at most 8.0 kg. English Wikipedia: the heaviest documented fish weighed 6.6 kg, and the IGFA record stands at 6.57 kg.
  • How old does it get? FishBase: up to 24 years. English Wikipedia: at least seven years, introduced fish in California up to 15. German Wikipedia: eight to ten years under natural conditions.
  • How long does it get? FishBase: 86 cm standard length — that is, measured without the tail fin. English Wikipedia: 86 cm. German Wikipedia: 85 cm.
  • When was the record set? English Wikipedia gives the IGFA record from the Nipigon River in Ontario once with the year 1915 and once with 1916 — in the same article.

Three names that lead to the wrong fish

  • “Tigerfisch” and “Elsässer Saibling”. GBIF also lists both German names for the brook trout itself — but according to German Wikipedia they are hybrids: the sterile tiger trout (with the brown trout) and the Elsässer Saibling (with the Arctic char). If you catch one of them, you don't have a pure brook trout on the hook.
  • “Beekforel”. GBIF also lists this Dutch name for the brook trout, but according to Dutch Wikipedia the beekforel is the brown trout, *Salmo trutta fario*. The Dutch name of the brook trout is bronforel.
  • “Speckled trout”. That's what the brook trout is called in parts of North America — but according to English Wikipedia a completely different fish carries this name too: *Cynoscion nebulosus*, also known in English as spotted seatrout — a marine fish from the drum family.

That leaves the question every article in this series starts with: when. Habitat, prey and habits are listed above, and they are fixed. What changes every day is everything else — light, air pressure, wind, water temperature —, and whether a day on the water is worth it is decided right there. That's what StrikeAhead calculates: it takes the conditions on your water and tells you when the trip is worth it. And because you can't know a new stretch of water, its spots and its rules from day one, StrikeAhead Pathfinder tells you who to go out with: curated guides and skippers, personally vetted before listing — licence and insurance —, with verified catches instead of promo photos, no paid ranking and, for you as an angler, no booking fee. The app tells you when, Pathfinder tells you with whom.