Rainbow Trout Reproduction
Rainbow Trout reach sexual maturity earlier than most other trout, including those charr with the trout name.
Spawning usually takes place towards the end of their first year. Rainbows will be between 12 and 16 inches/30 and 40 cm long.
In late winter and early spring the fish can be found migrating upstream to spawn in shallow gravel riffles or pools. These rivers and streams are usually mountain fed and are clear having very little turbidity and moderate water flow.
The female Rainbow Trout takes on the role of selecting the spawning location and begins to clear a nest, also known as a redd. She does this by turning on her side and flicking her tail towards the ground until enough gravel has been carried away. The nest is not very deep.
Rainbow Trout mating
Once the nest is ready, a male moves in to court her, showing off by shaking his body. If she accepts his advance, she moves to the nest and deposits her eggs deep into the nest. Depending on the age of the female or when she last deposited her eggs, she’ll deposit between 400 and 8,000 eggs. The male then fertilizes the eggs.
After spawning the female moves the gravel on the upstream edge back, covering the eggs providing them with protection from the current.
The Rainbow Trout eggs hatch between 3 weeks to 4 months depending on the water temperature. Migration begins when the rivers warm to between 44°F and 50°F/7°C to 10°C, which is shy of their ideal temperature range of 55°F to 60°F/12.7°C to 15.7°C.
The small trout then gather in groups and take shelter along the stream margins or protected lake shore, feeding on crustaceans, plant material, and aquatic insects and their larvae. The young trout eat mostly invertebrates, including insects.
Rainbows then stay in a similar habitat for the first 2 or 3 years before moving into the larger water of lakes and streams. It’s then that they turn to more of a diet of fish, salmon carcasses, eggs and even small mammals.
Unlike Pacific salmon, Rainbow Trout don’t change color to a bright red when they’re spawning. They’re not without a change though as they darken while spawning and change back after spawning to their lighter color.