Trout's Life Cycle

Trout are freshwater fish similar to salmon that are found in streams and lakes in North America, Asia and Europe. They prefer cool water and feed on other fish or insects. The life cycle of trout begins as an egg and goes through several phases before dying.

  1. Egg Stage

    • Trout lay eggs in the gravel of streams. These eggs gather nutrients absorbed by the passing water of the stream. Trout eggs are small--only a millimeter or two in length--and are characterized by a reddish translucence color with a small black dot or eye. A healthy egg has a central line indicating the development of the spine of the fish. To hatch, eggs require the water to be cool. Adequate water temperature ranges from 50 to 60 degrees Fahrenheit. It takes about 20 to 80 days for the embryos to develop.

    Alevin Stage

    • Once the egg hatches, it is referred to as an alevin. In this stage, the alevins remain in the gravel. Their bodies contain yolk sacks that serve to nourish the alevins through this stage. This stage will last as long as the alevin still have a yolk sack. An alevin resembles a tadpole with a bulbous ball that sits just behind and below the eyes. A long tail helps it to move in the gravel and makes its total length approximately one inch long. It will take take two to three weeks for its fins to develop.

    Fry Stage

    • The yolk sack reduces in size as the alevin uses the nutrients it provides. Once it is completely used up, the alevin becomes a fry. This is the first time the trout will act like a fish and start to emerge from the rocks and swim. It will stay in shallow, calm water and search for food in the gravel near shore. As a fry grows, it will get stronger and venture into deeper and deeper water and even hold positions against stream currents. The fry feed on insects and small fish or prey that fall into the stream. It may take two to three years for a fry to develop and grow into a young adult before it eventually migrates downstream.

    Adult Stage

    • Adults may live in either streams or lakes. They will feed on smaller fish, including smaller trout. Adult trout do not get as big as their cousins, salmon. Steelhead trout in Lake Superior get as long as 30 inches, being the largest type of trout. They may weigh as much as 15 pounds. Due to overfishing, most large adult trouts do not exceed 28 inches. Rainbow trout are much smaller, getting up to 15 inches in length and 8 pounds in weight. Trout live for three to four years.

    Spawning Stage

    • Spawning is the period when an adult trout will mate and fertilize the eggs. Even though a trout may live in a lake for its entire life, it will seek a stream to spawn and lay eggs. Most trout will spawn more than once in their life. An adult trout is usually at least three years old before it can start spawning. Spawning happens in the spring, often in April. The female scrapes a nest out, and the male fertilizes the eggs she leaves behind. A female spawns repeatedly until all her eggs are released, which may exceed 3,000 eggs.