Brook trout are prolific underwater breeders


My wife has a cousin who, like many anglers, lives for opening day of trout season. He loves native brook trout (He pronounces trout with long “o”).

Brook trout (Salvelinus fontinalis) inhabit spring-fed streams, beaver ponds, lakes, and rivers. They thrive in cold, oxygen-rich waters. And it is the only trout native to the eastern United States.

When brook trout disappear from streams, it’s often because the water temperature has increased due to poor forestry practices, overgrazing near streams, or suburbanization.

Water quality. Consider brook trout the “canary in the coal mine” of water quality. Unlike many life histories, the brook trout story begins in the fall, typically in October when days shorten and water temperatures dip to 39 to 49 degrees Fahrenheit.

Hormonal changes in male brook trout cause their bellies and lower fins turn crimson. The blue-haloed red spots that dot the brookie’s sides sparkle. Bright white bands line the edges of the fins. And their lower jaws grow and turn upward, though not as obviously as other members of the trout family.

Mating habits

The female’s outward appearance changes little. Internally, however, females turn into egg-making machines. Along the shores of beaver ponds, small rivers and even the tiniest spring-fed mountain streams, females choose the spawning site. The gravel and stones that will hold the eggs range from pea to walnut size.

And most importantly, there must be an upwelling of ground water directly beneath the nest or at least a current to carry away silt and sediments. When a female finds a site that meets her needs, she builds the nest, or “redd,” as ichthyologists call it.

She nestles herself tightly against the stream bed and anchors herself with her caudal fin. Then she violently swims in place, writhing her body back and forth. The hydraulics of her movements creates a saucer in the gravel and stirs up a cloud of debris — tiny particles of sediment, organic matter and insects that get swept away by the current.

A clean nest enables oxygenated water to bathe the eggs after spawning. The female’s nest-building activity attracts a dominant male to the redd. When the female is ready to spawn, she drags her anal fin through the nest.

The male swims by her side. In an act that lasts just a few seconds, the female opens her mouth widely and arches her back. Likewise, the male gapes, and a shiver-like action wracks his body.


Simultaneously, the female releases 15 to 60 eggs, and the male discharges a dose of milt (sperm). The milky cloud settles into the redd, and the spawn is complete. Typically 80 to 90 percent of the eggs are fertilized. The male leaves immediately, perhaps to search for another mate.

The eggs absorb water, swell, sink to the bottom of the redd, and become slightly sticky. The female completes the nest by using her fins to shovel a load of clean gravel atop the fertilized eggs. Then she moves on to build another redd.

Laying eggs

Over the entire spawning season, females lay a total of 400 to 600 eggs. The eggs overwinter in the redd and hatch in early March. In 35 degree water, eggs hatch in about 144 days. At 40 degrees, incubation takes just 103 days.

After hatching fry remain in the redd until their yolk is absorbed. This can take 23 to 80 days, depending on temperature. Small fry, less than an inch long, feed on macroscopic crustaceans. At an inch in size, they switch to a diet of larval insects. At four inches they feed on adult insects, and finally switch to small fish when eight inches long.

Adult brook trout eat anything they can swallow. Their diet includes mostly fish, but also includes frogs, salamanders, snakes and even mice and shrews. Brook trout are sight feeders and feed most actively early in the morning and late in the afternoon.

The growth rate of young brook trout varies with latitude and habitat. In lakes and beaver ponds, brook trout can reach three to four pounds in three years. But in cold mountain streams, a seven-inch brook trout is considered a trophy.

(Send questions and comments to Dr. Scott Shalaway, 2222 Fish Ridge Road, Cameron, WV 26033 or by email via my web site,

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Scott Shalaway, who holds a Ph.D. in wildlife ecology from Michigan State University, writes from his home in rural West Virginia. A former faculty member at Oklahoma State University and the University of Oklahoma Biological Station, he has been writing a weekly nature column for newspapers and freelancing for magazines since 1986. He can be heard on Birds & Nature from 3-4 p.m. Sunday afternoons on 620 KHB Radio, Pittsburgh, or live online anywhere at, or on the Tune-In radio app. Visit his website at or contact him directly at or 2222 Fish Ridge Road, Cameron, WV 26033.



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