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.


Fish Scale Lab with Sauk River Watershed District
  1. Using a forceps or scalpel, scrape against the grain of the fish scales to remove a few scales.
  2. Place the scales on the slide in a single layer.
  3. Add a small drop of glycerin on the scales and put a cover slip over them. Gently press down on the cover slip to remove any air bubbles.
  4. Starting from the center or focus on the fish scales count the annuli. Record your data on the table attached.
  5. Age at least three scales from each fish and record your data on the table attached.