Big Fish
Determining size of fish is difficult with sonar. This image shows big fish I was targeting this day and this is what I would see on the sonar. Notice the DownScan and the traditional sonar show a thick band and this is the best way to tell size.

Next, what is the target coming from the surface clutter to 15 feet. That is one of the trophy fish being released; the fish is swimming away from the cone so it disappears at 15 feet. The straight line is the fish and the air bubbles are easily seen.
The fish were 22-30 inch walleyes that gave my friend and Doc the best fishing day we have had together.