Fish I.D.
The Fish I.D. feature displays — as fish— targets that meet certain conditions. The microcomputer analyses all echoes and eliminates sur- face clutter, thermoclines and other undesirable signals.
The Fish I.D. feature displays symbols on the screen in place of the ac- tual fish echoes. There are three symbol sizes: small, medium and large. These show the relative size between targets. In other words, it displays a small fish symbol when it thinks a target is a small fish, a medium fish symbol on a larger target and so forth.
Fish 
arches 
Fish I.D. symbols
Underwater scene in normal fish arch mode (left). Fish I.D. menu with
the feature turned on (right).
Fish I.D. is an easier way for a sonar novice to recognize a fish signal return when he sees it. But, locating fish by symbol only does have some limitations.
Your sonar unit's microcomputer is sophisticated, but it can be fooled. It can not distinguish between fish and other suspended objects such as trotlines, turtles, submerged floats, air bubbles, etc. Individual tree limbs extending outward from a group of limbs are the hardest objects for the Fish I.D. feature to distinguish from fish.
To see what's under your boat in maximum detail, we recommend you turn off Fish I.D. and begin learning to interpret fish arches.
47