Why Do Trout Change Colors?

There’s nothing better than a vibrant pre-spawn color shift – but it’s not the only reason trout change colors.

A healthy small-stream brook trout. | Photo by Jasper Taback

If you were to follow a single trout over the course of a year, you’d notice that its coloration changes significantly. Most of us don’t have the time or technology required to do such a thing – but fish the same pool in a trout river at different times of year, and you’ll see what I mean. Trout change colors for a number of reasons – some you might expect, and some may come as a surprise. 

Camouflage

Trout have pigment cells in their skin called chromatophores, which expand and contract to alter the intensity of their colors – and they use them to adjust their coloring to better blend into their environment. As water clarity and vegetation color shifts with the seasons, trout adjust right alongside them. A neat example: trout tend to darken in the fall to match decaying leaves and brighten in the spring to match new green growth.

Spawning

Color changes during a trout’s spawning season are particularly noticeable, as males develop bright colors that let potential mates know they’re in good health and ready to spawn. An uptick in testosterone levels affects the chromatophores, causing their colors to shift drastically. You’ll see brook and brown trout go through these changes in the fall, and see them in rainbows and cutthroats as they get ready to spawn in the spring. 

Diet

Just like flamingos get their pink color from a shrimp-heavy diet, and redfish get their trademark tail spots from eating blue crabs, a trout’s diet can have a real impact on its coloration. Many of the aquatic insects and crustaceans that make up a trout’s diet have pigments called carotenoids, which become absorbed when they eat them. These pigments enhance the reds, oranges, and golds in their skin – the more they absorb, the brighter their colors get.  

Age

Juvenile trout have relatively muted colors – shades of brown and gray rather than red or gold – so that they can blend into the rocky, weedy nursery areas where they’re raised. As they grow and start feeding more aggressively, they start to develop richer colors. By the time they reach spawning age, they’ve grown enough that they can feed efficiently, contributing to the vibrant colors you’ll see during the spawning season. 

Adapt to Survive

If you thought that changing colors was just a cool thing that trout do, you're partially right – but there’s a significant evolutionary component to it too. All these color changes have to do with the adaptations a trout makes in order to survive and pass on its genes. Next time you catch a particularly colored up trout, you can feel good that you’ve netted a strong, healthy fish.