Hatching normally takes place from a few weeks to as much as four months after spawning, depending upon the water temperature. A few more weeks may be required for the tiny fry to emerge from the gravel. Upon
emergence, the small trout assemble in groups and seek shelter along the stream margins or protected lake shore, feeding on crustaceans, plant material, and aquatic insects and their larvae. Rainbow trout rear in
similar habitat for the first two or three years then move into the larger water of lakes and streams and turn more to a diet of fish, salmon carcasses, eggs, and even small mammals.
Age of onset of sexual
maturity varies markedly between individuals due primarily to such factors as population density, productivity of the aquatic environment, and genetic makeup. In the wild, male and female spawners as young as ages 3
and 5, respectively, have been found, but a majority of both sexes mature at age 6 to 7. Spawning frequency ranges from annually to once each three years. Rainbow up to age 11 have been observed spawning.
Among resident rainbow, those living in or migrating to large lakes with sockeye salmon runs generally grow faster and larger than fish which remain year round in streams.
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