Life & Times

The maturation of a trout, from egg to adult.

We oftentimes take the fish in our local waters for granted, but it’s a challenge for trout to even arrive at a catchable size in the first place. Here’s a look at how trout make the transformation from tiny eggs to the adults that anglers chase.

It all begins with spawning. Rainbow and cutthroat spawn in the spring while brown trout spawn in the fall, but the process is nearly identical for all three species. A female, or “hen,” selects a shallow, gravelly section of river called a “redd.”

After the eggs are fertilized by a male, the hen will cover the redd with gravel to protect against predators.

She then spends a few weeks prepping the area for her eggs. Once the redd is mother-approved, she’ll dig a hole and lay her eggs. After the eggs are fertilized by a male, the hen will cover the redd with gravel to protect against predators. A 12- to 14-inch trout will typically lay about 800 eggs.

The egg-hatching timeline depends on water temperature, with colder temperatures slowing development. Generally, brown-trout eggs hatch after six to 12 weeks, while rainbow eggs take only four to seven.

If fry persevere, they grow into “parr,” though only five to ten percent of parr survive their first year.

After hatching, the aspiring trout are considered “alevins.” They remain in the redd for two to four weeks, sustained by the remaining yolk sac. Once the sac is depleted of nutrients, the youngsters are considered “fry” and graduate from the redd to the river. This stage of a trout’s life is the hardest to survive, as a fry needs to find adequate food sources to sustain its energy-intensive growth. These juveniles—all competing for food—must find shallow water and habitat with a plethora of rocks and plants.

If fry persevere, they grow into “parr,” though only five to ten percent of parr survive their first year. Like fry, parr are territorial, fighting with each other for both food and shelter. Being larger and stronger, parr can venture into faster and deeper waters. To claim habitat, parr will travel downstream rather than exhausting their energy reserves traveling upstream.

As a trout’s strength fortifies with age, its diet also expands to larger insects and even younger trout. On average, a wild trout lives an average of six to seven years, but lifespans vary based on species, water temperature, predation, and fishing pressure.

A lucky fish might survive long enough to spawn, thus completing the life cycle and propagating the next generation of trout in our local waters.