Since most pond fish species grow to a constant pattern, the size and weight of a fish can be used to estimate the age.A more reliable method is to use the fish’s scales. Fish scales grow as the fish grows. A fish will grow faster in the summer than it will during the winter, this will cause rings to form on the scale. A broad, light band will form during the summer when the fish is growing faster, and a narrower, dark band will form in the winter when the fish’s growth slows. These bands, similar to those of a tree, can be counted under a microscope to determine the age. Fisheries and scientists also use bony formations in the fish’s ear, called otoliths, which produce much clearer rings when viewed under a microscope.