Fish
Brook Trout
Salvelinus fontinalis · also called brookie, speckled trout, squaretail
The brook trout is the fish of cold mountain water — a small, jewelled char that lives in the shaded headwater streams of eastern North America and disappears the moment those streams warm, silt up, or lose their trees. To an angler or a stream ecologist, finding wild brook trout means the water is still clean.
Overview
Salvelinus fontinalis is a member of the char genus, not a true trout, which is why it wears pale spots on a dark body: worm-track markings on the back, yellow flecks and blue-ringed red spots on the flanks, and white-edged lower fins. It is native to eastern North America from Labrador to Georgia, mostly in small, cold streams, and it eats insects, crustaceans, and small fish.
A gauge of clean water
Brook trout need water that is cold, clear, and well-oxygenated, generally under 20 °C. That makes them a living measure of stream health: a watershed that still holds wild brook trout is an intact one. Most spend their lives in a single headwater stream, though some run to sea as silvery “salters” and others grow large in lakes as “coasters”.
Squeezed at home, invasive abroad
In the southern Appalachians the native brook trout has been driven into the highest, coldest headwaters by stream warming, acid rain, logging sediment, and introduced brown and rainbow trout. Yet the brook trout, stocked worldwide for angling, is itself an invader elsewhere, displacing native cutthroat trout in the western US and galaxias fish in the Southern Hemisphere.
Status
The brook trout is Least Concern overall, secure in the north and in stocked waters, but its native southern and lowland range is shrinking, with many populations now confined to small, isolated stream fragments.
Brook Trout: common questions
Is a brook trout a trout or a char?
Biologically it is a char. It sits in the genus Salvelinus with the Arctic char, the lake trout, the bull trout, and the Dolly Varden, and not in the trout and salmon genera Salmo and Oncorhynchus. The clearest field sign is the spotting, since char have light spots, cream, yellow, pink, or red, on a darker background, while true trout and salmon have dark spots on a lighter background. The brook trout also has the wavy vermiculation on its back and the white-edged fins typical of char. The common name is simply an old one that stuck from a time before the groups were sorted out.
Why do anglers treat the brook trout as special?
Partly for how it looks, since a wild brook trout in spawning colour, with orange flanks, blue-haloed red spots, and white-piped fins, is one of the most striking freshwater fish in North America. Partly for where it lives, since catching one usually means fishing a small, cold, clear mountain stream in beautiful country. And partly for what it represents, since the brook trout was the original native trout of the eastern United States, the fish of colonial-era streams, and in much of that region it has been replaced by introduced species or lost entirely, so a stream with wild brookies is a link to how the water used to be.
What is the difference between a brook trout and a brown trout?
They are different fish from different continents that now often share the same streams. The brown trout is a true trout from Europe, introduced to North America in the 1880s, and it has dark spots, often red ones with pale halos, on a golden-brown body, with no vermiculation and no bold white fin edges. The brook trout is a native North American char with light spots, worm-track markings on the back, and white-and-black edged lower fins. Brown trout tolerate warmer, siltier water and grow larger, and where they have been introduced they tend to outcompete brook trout and push them upstream into the coldest headwaters.
Can brook trout and other trout interbreed?
Yes, in a couple of cases, though the hybrids are usually sterile. A brook trout crossed with a brown trout produces the tiger trout, a boldly vermiculated fish with striking maze-like markings, which occurs rarely in the wild where both species spawn at the same time and is also bred deliberately for stocking. A brook trout crossed with a lake trout, both being char, produces the splake, which unlike the tiger trout is fertile and is stocked in some lakes because it grows faster than a brook trout and matures earlier than a lake trout. Pure wild brook trout populations are the conservation priority.