What Do Fish Look Like on a Fish Finder? Every Sonar View Explained

What do fish look like on a fish finder? On a standard scrolling 2D screen, most fish show up as arches: curved marks, thickest in the middle, hanging between the surface and the bottom line. That is only one view. On down imaging a fish is usually a small spot over sharper structure, on side imaging it is a mark off to one side of the center strip, on live sonar it is a shape that moves in real time, and on an ice flasher it is a colored band that rises and falls on a dial. Turn on fish symbols and the unit swaps many of those returns for an icon.

This guide goes mode by mode: what a fish looks like, why, and what else can leave a similar mark. It assumes you can already find the bottom and the depth scale. Reading the whole screen, including gain and range, has its own walkthrough, and so does how sonar builds the picture. The descriptions come from Garmin, Deeper, and Vexilar documents, linked where cited; other brands use different names, so match each point to your own manual.

What Do Fish Look Like on a Fish Finder in 2D Sonar?

Traditional 2D sonar sends a cone-shaped beam down and draws each echo at its depth as the screen scrolls. Deeper’s explainer on how sonars work calls the result an arch or “fingernail” shape. A fish crossing the cone returns echoes from one edge, then the middle, then the other edge, and the edge echoes travel slightly farther, so both ends of the mark are drawn a little deeper than its peak. The shape depends on how the fish and the boat move:

• Full arch. The fish moved through the whole cone.
• Half arch or thick dash. The fish crossed only part of the cone. Deeper says to look out for these; they are still fish.
• Straight line. Deeper’s guide to reading its CHIRP+ 2 display describes a straight line as a fish right under the sonar, and says you see a line, not an arch, when the sonar and the fish are both stationary. Its sonar explainer adds that one still fish under a still sonar can produce a constant stream of fish icons.
• A lopsided or broken arch. The Garmin Fishfinder 340C owner’s manual notes that suspended targets do not always appear as perfect arches because of boat speed, fish orientation, or other conditions.

Frequency changes the size of the mark. The Garmin STRIKER Vivid owner’s manual says lower frequencies use wider beams and that wider beam widths generate larger arches for fish target returns. On a split-frequency screen, expect the same fish to look bigger on the low-frequency side.

Single Fish, Schools, and Baitfish

One arch with clear water around it is usually a single fish. Deeper’s CHIRP+ 2 guide says a school can appear as groups of small arches or as dense clusters with intense coloring, depending on the type of school. Its guide to reading the Deeper display describes baitfish as dashes, lines, or dots, usually suspended rather than on the bottom, with bait balls showing as a cloud or cluster, and says the standard color display of the Deeper app shows bait yellow rather than the green used for vegetation.

The working read: a dense cloud without distinct arches is most likely bait, and separate, thicker arches at the edge of or under that cloud are the marks worth a cast. The STRIKER Vivid manual says CHIRP can distinctly identify targets like individual fish in a school; how CHIRP separates targets is covered in its own guide. A big school near the bottom can also fool the depth reading: the Fishfinder 340C manual warns that large schools of fish or dense structures close to the bottom can affect water depth readings.

Fish Symbols: What the Icons Mean

Most units can replace raw returns with a fish icon. Garmin calls the setting Fish Symbols, and the STRIKER Vivid manual says it sets how the sonar interprets suspended targets, with four options: symbols alone, symbols with target depth, symbols over the background sonar, or symbols over the background sonar with depth. The background options keep the arch, cloud, or line visible under the icon, so you can judge whether the unit flagged a fish, a limb, or a clump of weeds.

Icon size is an interpretation too. The older Fishfinder 340C manual explains that its symbols come in small, medium, and large sizes based on the size of the sonar return, and that in dual beam mode, symbols from the narrow beam directly under the boat are solid while those from the wide beam out to the sides are hollow. The STRIKER Vivid’s fish alarm uses similar tiers: all sizes, medium or large only, or large only. A bigger icon means a stronger return, not a heavier fish or a particular species, and Deeper’s display guide says even the most advanced units aren’t 100% accurate at interpreting returns. Other makers use their own names and logic for fish icons, so check what each size means in your manual.

What Fish Look Like on Down Imaging (ClearVü)

Down imaging trades the cone for a thin slice of water. Garmin’s scanning sonar overview describes ClearVü as down-imaging sonar that shows a high level of detail in a narrow window under the boat. Garmin’s GT20-TM transducer page says that transducer displays fish arches as well as clear pictures of objects, structure, and fish passing below the boat; it carries a traditional channel alongside the ClearVü channel.

On the image itself, fish rarely draw the clean arches of 2D. A fish usually passes through the thin beam quickly and leaves a small spot or short streak above or beside the cover. Stetson Blaylock, writing on Garmin’s blog about fall fishing with ClearVü and SideVü, refers to “those spots on your graph” and describes idling while they look for shad balls with both views.

Imaging is stronger on shape than on fish. Garmin’s transducer selection guide says its traditional sonar is great for picking up soft targets, such as fish, that scanning sonar might miss. If the ClearVü picture shows a brush pile with nothing around it, check the 2D window before you move on.

What Fish Look Like on Side Imaging (SideVü)

Side imaging aims thin beams out to the left and right. The STRIKER Vivid manual calls SideVü a search tool for finding structure and fish. Its labeled example puts the transducer at the center line, the water between the boat and the bottom on either side of it, and logs, old tires, and trees farther out; it does not label an individual fish.

In practice, a fish on a side image is a small mark, often brighter than the bottom around it, either in the open strip near the center or over the bottom farther out. A fish holding above the bottom can also block part of the beam and leave a darker gap on the bottom beyond it, the same way a log or rock does. Treat these marks as leads: note how far out one sits, turn, and pass over it with 2D or down imaging. If you are still choosing between side and down imaging, the trade-offs are covered separately.

Marks on a side image are not always the fish you want. In a Garmin blog post on pairing sonar with an underwater camera, Steve Pennaz describes scanning a Great Lakes reef with SideVü for smallmouth, seeing what looked like a reef loaded with fish, and finding with a camera that the marks were suckers. They also write that soft-stalked grass such as milfoil can lie flat in current and look like a school of four to five fish on sonar.

What Fish Look Like on LiveScope and Other Live Sonar

Live sonar drops the scrolling history. Garmin’s live sonar overview says that unlike traditional or scanning sonars that display historical data, live sonar gives a real-time look below the surface, and compares the difference to a photograph versus livestreaming video. The selection guide describes LiveScope as showing live scanning sonar images of structure and swimming fish.

So a fish is not an arch here. It is a shape that moves across the screen as the fish swims, and bait usually shows as a cluster that changes shape. In Garmin’s LiveScope Plus press release, a Garmin vice president says the system lets you see your fishing line, your lure, and how fish respond to it. The picture shows only where the transducer points, though; the selection guide notes that on a trolling motor mount, the sonar image corresponds to the position of the motor. For what LiveScope is and how its modes work, see the separate guide.

What Fish Look Like on an Ice Fishing Flasher

A flasher shows echoes on a round dial, in real time. The Vexilar FLX-8 instruction manual says fish, bait fish, and even your lure show anywhere between the zero mark and the bottom mark, and that fish, being much larger than bait, appear as stronger signals. Its color code:

• Red: strong signals, such as the bottom, heavy vegetation, and large fish. Smaller objects such as bait fish can also show red when directly under the transducer.
• Yellow: medium signals from smaller objects and softer bottoms.
• Green: weak signals from small objects such as light vegetation and bait fish.

A fish on a flasher is a band of color at its depth that moves up or down the dial. With gain set properly, the manual says your lure appears as a weak signal, small next to the fish; as you lower it, a curious fish rises, and when the two signal lines meet, it is time to be ready for a strike. A thin green line right on the bottom may be a fish just up off the bottom, per the same manual. Setting up a flasher on the ice has a separate step-by-step guide.

Confirm a Mark With a Second View

No single view settles what a mark is. Use 2D or a flasher to confirm something is there, imaging to see what it is holding on, and live sonar to watch it react. Don’t skip the second look when a mark matters. If you are comparing complete units, browse the Fish Finders section, and see How We Review for how we assess gear.

Frequently Asked Questions

What does a fish look like on a fish finder screen?

On a scrolling 2D screen, usually an arch between the surface and the bottom, or a half arch if it clipped the edge of the cone. A fish under a stationary boat draws a straight line. On imaging it is a small mark, on live sonar a moving shape, and on a flasher a colored band at its depth.

What do fish look like on a Garmin fish finder?

Arches in the traditional view, which Fish Symbols can replace or overlay with icons. ClearVü shows fish as small marks around structure below the boat, SideVü as marks off to either side, and LiveScope as shapes moving in real time. Your model’s owner’s manual lists the exact menu names.

Does a bigger arch mean a bigger fish?

Not by itself. Deeper’s CHIRP+ 2 guide says the best indicator of fish size is the width of the arch, and a long arch often just means the fish stayed in the cone longer. A wide, low-frequency beam also draws larger arches than a narrow one for the same fish.

Why do I see fish icons but no arches?

Fish Symbols is probably set to show icons only. Switch to an option that includes the background sonar so the arches appear under the icons, or turn symbols off and read the raw returns.

Can a fish finder tell what kind of fish it is?

Not reliably. Icon size reflects return strength, and Pennaz’s reef of apparent smallmouth turned out to be suckers on camera. Garmin’s LiveScope Plus press release quotes its vice president saying live images let anglers distinguish between species, but that is the maker’s claim; an underwater camera is the surer check.

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