How to use Fish Finders by Lowrance Electronics
You may see fish arches while trolling with the unit in a 0 - 60 foot scale, however it it much easier to see the arches when using the zoom feature. This enlarges all echoes on the screen. Turning the zoom feature on gives you a screen similar to the one at left. The range is 8 - 38 feet, a 30-foot zoom. As you can see, all targets have been enlarged, including the bottom signal. Fish arches (A & B) are much easier to detect, and important structure (C) near the bottom is magnified. This also shows small fish hanging just beneath the surface clutter (D). The above steps are all that's required to manually adjust your sonar unit for optimum fish finding capability. After you've become more familiar with your unit, you'll be able to adjust the sensitivity properly without having to look for a second echo. This picture came from the Lowrance Electronics site and is the property of that site.
Look at this link it is from Lowrance but will work for most other, fish arch finders. Follow these steps on setting up your electronics and spend time looking for fish. Get some markers, see what you think are fish, throw them out, come back around and fish the spot. Don't get discourged, not all fish are feeding, when you see them. I have included a pic from this info. http://www.fishfindercity.com/fitiandin.html . I will include some actual pics in later posts.