Fish Scale Lab

When a fish is hatched, it is covered with tiny scales. The center of an older fish's scale, called the focus, represents the scale of the newly hatched fish. As the fish grows, the scales develop circular growth rings around the focus. Each growth ring is called a circulus (plural: circuli). Like a tree, the fish grows faster during the summer when the temperature is warmer and there is more food available, and the circuli are spaced father apart. During the winter, growth slows down and the curculi are very close together. When the circuli are close together, they form a dark ring called an annulus (plural: annuli). Each annulus represents a year's growth, so by counting the annuli, it is possible to estimate the fish's age.