Walleye and sauger are often confused.  In walleye, the lower lobe of the caudal fin is whitish, and there is a dark spot at the posterior end of the spinous dorsal fin.  Reaches length of 36 or so.  Sauger is similar but lower lobe of caudal not whitish and no dark spot.  Does have a black spot on the basal portion of pectoral fin; reaches about 15.  Both are often deep-water fish, not very good fighters, but great eating!