Fish with bones have scales. Some fish, such as gar, have heavy, plate-like scales called ganoid scales. Other fish have thinner scales. Fish scales form rings as they grow. During the cold months, scales grow more slowly and leave a ring on the scale. Like rings on a tree, you can count rings on a scale for clues on the age of fish. This is easier to do with fish that live where winter temperatures are cooler. Fish without scales include catfish, sharks, most eels, lampreys and rays.