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Many fish change colors as they age. One example is the bluehead wrasse, which is yellow and white as a juvenile/female (left) but adopts the blue head coloration as an adult male (right). Credit: Nick Hobgood, CC BY-SA 3.0
One of the changes that goes along with aging is hair color. Red, blonde, black—regardless of the original color, our hair almost always turns gray or silver.
Fish don’t have hair, but many of them do change color as they age. They can take on different color schemes as they move through different stages of life.
Fish change color for many reasons. Some of the changes happen in a flash—a fish might blend into the background to protect itself from predators. Other changes are more gradual. A fish might change color when it switches gender, for example.
Many fish keep the same basic scheme throughout life—especially those that spend their lives in the open ocean. The ones that are more likely to change color as they age are those that move around—they’re born in one place, but they shift habitats as they grow and mature.
Salmon, for example, have stripes when they hatch, in rivers and streams. When they move out to sea, though, they take on a smoother, silvery tone. American eels, on the other hand, are colorless when they hatch, in the open ocean. But as they mature, and move into rivers and streams, they turn dark on top and light-colored on the bottom. And when they return to the ocean to spawn, they turn silvery bronze.
And in some species, only some members change color as they age. Only males of the bluehead wrasse adopt the namesake color, and only when they mark out a territory—a colorful signal that they’re ready to take a mate.
