How To Read A Fish Finder Screen – Know What Fish look like

The advances in fish finding technology have been phenomenal over the last decade.

Anglers today have unique insights into the underwater world that your grandfather never dreamed of.

However, one thing hasn’t changed, and that’s the need to interpret the images on your screen.

While today’s digital color readouts are a world away from the monochrome pencil on paper of your grandfather’s era, you will still need to know what all the shapes and colors mean.

Let’s have a look at the basics. You can become quite proficient quickly between this article, and the instructions in your fish finder box.

Whether you’re down scanning or side-scanning, understanding the images on screen is the key to helping you find fish and catch fish.

Before we look at some basics, the most important path to becoming a fish finder expert is to learn how to read a fish finder screen perfectly.

Learning About Your Fish Finder Out on the Water

I remember people explaining the readout on a fish finder to me while out fishing. 

Interestingly, I recall just how much I didn’t take in. Yes, I learned some things about shapes and colors, but I was out there to fish, not a tech lesson.

It wasn’t until I had my own fishfinder that I discovered I was pretty clueless and needed a solution to understand what the heck I was looking at on-screen.

If you’re anything like me, instructions are a little like government forms, a sure path to fury – Great for the basics, but only a guide for experiential learners such as myself. I had to learn it out on the water.

With some loose basics, I motored to some clear water, where I knew the subsurface and the structures on the lake bed. Most importantly, I didn’t take any fishing gear, as that would be a distraction.

This trip was all about learning what my fish finder was telling me. And the best way to do it was to scan an area that I knew like the back of my hand.

Water depth varied from 6 to 15 feet, and there was a great mix of mudflats, grass beds, reefs, and barren sandy expanses.

I worked these locations very slowly, peering over the side of the boat, repeating passes over certain structures. My wife would indicate things she could see, calling out structures as I studied the screen.

I could ramble on for ages about this experience, but I’m sure you can see how this personal lake bed survey allowed me to understand what I saw on the screen.

When you know exactly what you’re scanning, interpretation becomes quite easy, and you can apply these structure/display connections everywhere.

This discovery trip was a revelation. I learned plenty about my fish finder display. 

The only downside was that I worked out the thick yellow banana shapes on my screen were trophy fish that I had not so much as a handline to target.

With a little internet research, a moderate understanding of the Simrad instructions under my belt, and a day on the water dedicated to sonar tech, I was able to get a pretty good grip on reading my fishing cheat machine.

Here are some great videos that offer beginners a handy insight into the basics. This one is very good and deserves a subscription.

The next one has some pretty good diagrams that help you visualize the process. Check them out, and come back, as this article will review what you’ve discovered.

How To Read a Fish Finder – Understanding the Display

As you have just discovered, having watched the videos above, your display provides you with a heck of a lot of information, from fish size and depth in the water column to the sea bed structure and composition.

Here are some core things to remember. 

There’s a lot to learn and take in when discovering the full functionality of a fish finder. From mapping and GPS to screen adjustments and view settings such as split screens.

The main aim of this article is to focus purely on the critical information you see on the screen and what it means.

Fish Arches vs Fish Dots

Fish will appear as arches on the screen. The arches vary in color and shape relative to their position in the cone or range of the sonar.

Importantly, the arch will vary depending on the speed of the boat. The slower the boat, the longer the arch. If you’re moving quickly, the fish will be displayed as dots.

It’s because of this that the size of the arches is not always indicative of fish sizes. 

A very slow-moving boat passing a fish in the center of the cone can be read as quite a large fish.

A fish on the edge of the cone of a faster-moving boat may appear small. We need other information to determine fish size.

Fish Icons

Many fish finders (Garmin for example) interpret the arches for us and can replace the arch with a fish icon.

It will give us depth information and can also add information such as the background sonar information.

Many anglers find this preferable to see fish on the screen, as it cuts through the noise of other colors, blobs, and shapes.

However, this method is far from perfect and will at times show fish where there aren’t any at all. 

Often, fish finders will recommend you turn off the fish icon when trying to determine size.

Evaluating Fish Size With a Fish Finder

It’s important to note that no sounder can give a perfectly accurate fish size. It’s an indicator only.

For example, a thick yellow arch might indicate a large fish, but it’s not a guarantee. What we’re seeing depends on how our sonar is set.

When we’re looking for fish, we’ll have the sonar set to a wide capture to cover more ground. 

In this setting, it’s possible for a fish to appear large but actually isn’t. It’s more its position in the sonar beam.

However, if you’re looking for large fish specifically, a narrow scan that shows up a thick strongly colored yellow line is nigh on certainly a big fish.

However, if you’re looking for large fish specifically, a narrow scan showing a thick, strongly colored yellow line is almost always a large fish.

It’s important to remember that you may see full or patricidal arches on screen. A partial arch doesn’t necessarily mean a smaller fish. It simply means it did not pass the full range of the sonar.

Sonar bounces from the fish’s swim bladder. Anglers can learn to identify and differentiate between fish species with experience, local knowledge, and a good fish finder.

Over time, you will understand more as you catch the fish you’ve just scanned, and therefore can compare the size to what you saw on screen.

What do the Colors Mean on a Fish Finder

Different brands use the color palette differently, but they all will show stronger color reds/yellows the harder or denser and object. 

The stronger the echo return, the stronger the color on the screen.

For example, the big fish in a narrow scan on a Simrad will appear as a very strong yellow. A dense school of baitfish will show up red on a Lowrance.

If the lake or river bed will show up as a thick dark yellow or red if it’s a solid, hard bottom. 

A more muddy or porous sandy bottom will have less color, showing as a thin line sitting above the harder, thick, and stronger colored section beneath it.

Blues can indicate structures and features on the edge of the beam. It can also show areas of dead, poorly oxygenated water and temperature changes.

Locating Baitfish on a Fishfinder

Baitfish will often show up as solid balls or clouds. The color will often vary depending on the density of the school.

On a Simrad or Hummingbird, baitfish will show up as a solid ball or cloud of yellow. On a Lowrance, the baitfish will show up as a red cloud or ball.

It’s important to know that what you see on the sounder has already happened, and you’ve passed it. It’s history. 

A snapshot is taken as you’ve moved over the fish or school. This is where a touch screen and plotter are invaluable. 

You can simply touch the school on the screen, and the plotter will give you a GPS location and path back to the spot in which they were scanned.

Remember, fish move, so there’s no guarantee they’ll be there when you motor back, but the chances are good.

Finding Monster Fish on Your Display

As I mentioned earlier, big fish will show up as a thick yellow arch. You’re using this information in combination with other info. But the thickness of the arch is the key.

Firstly, you’re taking your knowledge of the location and the types of fish and sizes that inhabit the waters you’re fishing.

Secondly, you’re noting the structure and cover in the area you’re fishing, as well as depth and temp. Now, You’re starting to draw a picture.

Now you’re looking for signs of bait clusters. Look for thick yellow arches on the fringes of the bait cluster, or better still, right in the middle of the cluster. 

That’s large fish feeding on small fish.

With this information, you can deduce that not only are larger fish there, but they’re also actively feeding.

See Also: The Top Fish Finders For Bank Fishing

How to Read Underwater Topography on a Fish Finder Screen

We all like to see lots of arches, particularly thick yellow arches. But the bathymetric information, or geography of the sea bed, tells us important information about fish habitat. 

Fish like structure, cover, and contours

A wide beam gives you a basic outline of structures and contours and will do this even at a pace. 

Moving slowly with a narrow beam will show up detail, with rocks and reefs showing as solid yellow, grass, and weeds showing as vertical lines of variable color intensity.

The bottom will be the hardest line at the base of the screen. A thick yellow line, for example, shows a more solid bottom. 

A thin, less intensely colored line will show a more porous bottom, such as mud or sand.

Contours show up very easily and are read in conjunction with depth. A good sonar will show changes or patches of water temp variation, with deep blues an indication of a patch of denser, cooler water.

How to Read an Ice Fishing Flasher

Fishfinders and ice fishing flashers do the same thing, taking the same information with a sonar beam.

The difference is in the way the information is displayed. With an ice fish finder, information is routed to a circular display, which uses color indicators the same way a fish finder does.

In some respects, a flasher is easier to understand with its more rudimentary display

Check out this video for an outstanding summary of reading an ice fish finder. In fact, I have not seen them so well explained so quickly and concisely. Awesome for the beginner!

Also read our guide on the differences between an ice fishing fish finder and a flasher.

Frequently Asked Questions

Also Read:

Is Side Imaging Worth it?

Is Down Imaging Worth it?

Sharing is caring!