Sonar features explained
Fish ID Symbols on Your Fish Finder: Should You Turn Them Off?
Out of the box, many fish finders show fish as little fish-shaped icons, sometimes with a depth number beside each one. It looks friendly and it is easy to understand. It is also one of the first settings experienced anglers switch off.
This guide explains how fish ID (also called fish symbols, fish alarms with icons, or similar names depending on the brand) decides what is a fish, why it gets things wrong, and when it is actually useful. It also covers how to read the raw sonar returns once the icons are gone.
How fish ID decides what is a fish
A fish finder receives echoes from everything in the cone: the bottom, weeds, timber, bait, bubbles, fish and sometimes the thermocline. Fish ID software looks at those returns and applies rules. In general terms it considers things like:
- Whether the return is separated from the bottom.
- Its strength and size compared with other returns.
- Its shape over several pings (fish moving through a cone often produce an arch).
- Whether it looks like a single target or a cluster.
When a return matches, the unit replaces it with an icon. Different units use different rules, and manufacturers do not publish the exact logic, so behavior varies by brand and model.
Where fish ID goes wrong
| Situation | What fish ID often does | What the raw sonar shows |
|---|---|---|
| Fish tight to the bottom | Misses them; they blend into the bottom return | Small humps or arches just above the bottom line |
| Fish in weeds or brush | Labels the cover as fish, or misses fish inside it | Fish arches or marks distinct from cover texture |
| Bait schools | Draws many fish icons, or one big icon | A cloud or ball, often with larger marks around it |
| Bubbles and surface clutter | Icons near the surface | Random speckle near the top |
| Thermocline | Icons along the layer | A faint horizontal band with real fish along it |
| Stationary boat | Inconsistent; may show long lines as fish or nothing | Horizontal lines for fish holding in the cone |
The biggest practical loss is context. A raw arch tells you whether a fish is sitting on the bottom, hovering over brush, suspended at the edge of a school, or chasing bait. An icon floating in empty space tells you only that something reflected sound.
What raw arches tell you that icons do not
Relationship to cover
Fish holding tight to a brush pile, on top of a weed bed, or on the side of a rock.
Relative size
Thicker, longer arches are often larger fish or fish closer to the center of the cone. Relative, not exact.
Behavior
Fish rising toward bait, holding still, or scattered and moving.
School shape
A tight ball of bait vs a loose spread of larger fish.
No fish finder measures fish size reliably from 2D sonar. Arch thickness depends on fish size, position in the cone, angle, boat speed and settings. Icons that label fish as small, medium or large are making a rough guess from return strength.
When fish ID is useful
Fish ID is not useless. It suits a few situations:
- Brand-new anglers learning to connect icons with what they catch, especially on simple units.
- Casual trolling for suspended fish, where the depth number beside each icon is a quick guide to how deep to set lines.
- Fish alarms, on units where an alarm only triggers through fish ID. Useful while doing something else, though prone to false alerts.
- A small second screen you glance at occasionally.
Some units can show icons and raw arches together, or show the depth number over raw arches. That combination gives the best of both: the full sonar picture plus a quick depth label.
How to switch it off and read raw sonar
- Find the setting. Fish ID usually sits in the sonar page menu or sonar settings, under a name like fish ID, fish symbols or fish icons. If you cannot find it, check the manual.
- Turn icons off, or choose an option that shows depth only over raw arches.
- Adjust sensitivity. With icons off, you may need slightly more sensitivity to see small fish arches clearly.
- Set scroll and boat speed. Arches form best when the boat moves at a slow, steady speed. Stationary or very fast boats produce lines or smears instead.
- Use zoom or bottom lock to separate fish close to the bottom.
- Compare with what you catch. Over a few trips you will learn what your target species looks like on your unit.
Reading common shapes without icons
Full arches
A fish passing through the cone while the boat moves steadily often draws an arch: it starts at the edge of the cone (farther away, so slightly deeper), comes closest at the center, and moves away again.
Half arches and lines
If the fish enters or leaves part way, or the boat is stationary, you may see half arches or horizontal lines. A horizontal line often means a fish holding still while you hover.
Clouds and balls
Bait schools usually look like clouds or dense balls of small marks. Larger, distinct marks around the edge of a bait ball are often predators.
Vertical marks
Weeds often appear as vertical, fuzzy lines rising from the bottom. Timber appears as stronger vertical lines or branching shapes.
Fish ID with imaging and live sonar
Fish ID icons are usually a 2D sonar feature. Down and side imaging generally show fish as bright dots or small blobs, sometimes with a shadow on side imaging. Forward-facing live sonar shows moving targets in real time. In those views, reading the raw image is the norm.
A practical way to make the switch
If you have relied on icons for years, turning them off can feel like losing information at first. A gradual transition helps:
- Run a split screen for a few trips with icons on one side and raw sonar on the other, if your unit allows it. Watch which raw marks become icons and which do not.
- Note the misses. Every time you catch a fish that never showed as an icon, look at what the raw view showed at that moment. Those are the marks fish ID is hiding from you.
- Note the false alarms. When icons appear over weed tops or in a bait cloud, compare with the raw view. You will quickly learn the textures of cover versus fish.
- Save a raw-sonar page as your default once you are comfortable, and keep the icon page available for casual days.
If your unit can save screenshots, grab one whenever you catch a fish. A small library of what your target species looked like on your own screen is the fastest way to learn raw sonar.
Bottom line
For most anglers, turning off fish ID and learning to read raw arches gives more information: what fish relate to, how they behave and where they are in relation to the bottom. Keep fish ID on only if you are brand new, if it drives an alarm you rely on, or if your unit can show a depth label on top of raw arches. Either way, the real skill is matching what you see on screen with what you catch.
FAQ
Are fish ID icons accurate?
They are a guess. They often miss fish near the bottom or in cover and label weeds, bubbles or bait as fish.
Can a fish finder tell how big a fish is?
Not reliably. Arch size depends on fish size, its position in the cone, angle and settings. Size labels on icons are rough estimates.
Why do I see fish icons in the weeds?
Weeds and brush can produce returns that match the fish ID rules. Turn icons off to see the cover and the fish separately.
Should beginners use fish ID?
It is fine for learning, but compare icons with raw arches when you can. Most anglers switch them off once they learn to read the screen.