Difference between depth finders and fish finders


​What is the difference between a "depth finder" and a "fish finder"?  Are they the same thing?


​A "depth finder" or "digital depth finder" is exactly that--a display of depth information.  This is a simple display of the depth of water under the boat in digital read-out. This is more commonly utilized for shallow water depth detection, when a graphic display is not required. 
A "fish finder" uses the same or similar transducer and actually gives a graphic, video image of the water and bottom under the boat, as well as several seconds or minutes history. This video image will show any objects detected by the transducer. This would include the bottom as well as fish, wrecks, etc. that would be useful to fisherman.