Count the Rings: How to Tell a Fish’s Age from Its Scales

How can you tell how old a caught fish is? By examining its scales. When a fish hatches from its egg it already has the beginnings of its scales, and it adds more scales as it grows. Each individual scale also grows as the fish gets bigger.

In summer, when fish are actively feeding, each scale forms a light band of larger cells. In winter, fish often shelter in deep holes and pools, enter a lethargic state, and stop feeding. That slowdown creates a dark band of smaller cells along the edges of the scales, and these bands continue to accumulate as the fish ages.

Count the light bands on a scale to determine how many years the fish has lived.