The Sauger (Sander canadensis) and Walleye (Sander viteus) are two distinct species of fish, but they are closely related. When it comes to identifying the difference between a Sauger and a Walleye, the most important thing to remember is their size. A Sauger is typically smaller than a Walleye, and they have a more slender body. They also have a wider head and a flatter belly.