You are looking at a fish a fish otolith (like a saccule or utricle in a human ear) though a microscope. How you tell a fish age is like counting rings on a tree. You can also tell the length of the fish though out its life span by just looking at the otolith, But you must have a certain program to do that.
Large mouth bass otolith
Example:The A are the years.
Credit to this picture goes to--http://elearning.uaf.edu/cc/otolith/analysis/whole.htm