Rainbow Trout (Oncorhynchus mykiss) are a western North American species, native to the Pacific slope from California to Alaska, and non-native to Pennsylvania streams. In a turn-of-the-century effort to restore Pennsylvania’s degraded trout fishery, Rainbows were introduced throughout the state.
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IdentificationRainbow Trout are silvery-gray to dark-green on the back and sides. They have a pinkish or reddish lateral stripe, sometimes with lavendar or orange overtones, from the gill cover running the length of the fish to the tail. The caudal fin has rows of small dark spots, and there are more small blackish spots sprinkled on the head and sides, and spotting on the dorsal and adipose fins. The belly is whitish. The lower fins are pale-pink without spots.
At spawning time, males become deeply colored with an intensely red side stripe. Steelhead can be separated from similar-looking Coho and Chinook Salmon by looking at the inside of the mouth. The mouth is completely white in the steelhead. In the salmons, the mouth has some gray or black. Steelhead and other deepwater, big lake Rainbows are more silvery than stream fish, with less of a side stripe. Great Lakes steelhead can grow to 30 inches and larger. The Pennsylvania state record for a Rainbow Trout is more than 20 pounds. |
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Life HistoryRainbow Trout are considered spring spawners, but steelhead may enter streams to spawn from late fall through spring. Spawning takes place when the water temperature is about 50 degrees, over gravel beds with good water flow. Rainbow Trout move upstream to find the proper spawning area. Rainbows in lakes seek tributary streams. Like other trout, the female Rainbow prepares the nest depression by turning on her side and “kicking” against the bottom gravel with her body and fins. Male Rainbows are aggressive on the spawning grounds, driving other males away from the female’s nest. When the actual spawning takes place, several males may be beside the female. The females produce several hundred to over 12,000 eggs, depending on their size. After the eggs are deposited into the gravel and fertilized, no parental care is given. The eggs hatch in four to seven weeks. The fry take up to another week in the gravel to absorb the yolk sac. Then they become free-swimming. Most Rainbows are sexually mature when they reach about three to five years old.
Documentation of successful natural reproduction in Pennsylvania is rare. Self-sustaining populations of Rainbow Trout are found only in a few scattered streams. But mature Rainbows, especially steelhead that have run up Lake Erie tributaries, successfully spawn and produce young. However, adult returns are mostly comprised of hatchery-released fish. Unlike salmon, which die after spawning, steelhead can spawn again, returning to the ocean or large lake to grow even bigger before the next year’s spawning run. Steelhead also follow other spawning fish migrating upstream and prey on their eggs and young. Rainbows feed on aquatic and terrestrial insects, crayfish and other crustaceans. Rainbows also eat fish, as well as plankton, snails, leeches and fish eggs. They take a variety of anglers’ flies, lures and baits. Rainbows have been intensively cultured in fish hatcheries. Strains have been developed that are of various colors, are tolerant of warm water, grow rapidly, resist disease and spawn at times different from the rainbow’s natural spawning time. The lifespan of the steelhead in the Great Lakes is six to eight years. Small-stream Rainbows may live only to be three or four years old. |
Made possible through a unique partnership between the Pennsylvania Council of Trout Unlimited (PATU) and the Pennsylvania Fish and Boat Commission (PFBC), Pennsylvania Trout In the Classroom (PA TIC) is an interdisciplinary environmental education program in which students learn about current and past impacts, management, and protection and enhancement opportunities of Pennsylvania's coldwater resources, while raising trout in the classroom.
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