First, a little science; fish can be aged by examining scales or various bones (scale exams leave a live specimen). Hard body parts grow as the fish grows, adding annual rings similar to the rings in trees. Under a microfiche reader, panfish scales look a bit like a blend of a fingerprint and a common seashell. Scales get larger as the fish grows by adding to the outside edge. Because fish are cold-blooded and grow very little during winter, a thicker ring is formed, giving a year mark.