How To Read A Fish Finder

One of the most important fishing accessories to have emerged in recent years is the fish finder.

The effectiveness and versatility of fish finders are what make them so useful. A fish finder can be used by fishermen, anglers, divers, as well as other professionals that spend them in water.

For many anglers, both beginners and experts, reading a fish finder can be challenging. This is because they do not understand how it works and what the display on the screen represents.

In this article, we’re sharing how to read a fish finder screen.

how to read a fish finder
The fish finder of the charter boat Miss Susie II is seen after departing from Harbor Island Marina in Solomons, Md., on April 25, 2014. (Photo by Steve Droter/Chesapeake Bay Program)

How To Read A Fish Finder Screen

The screen of a fish finder can provide you with a lot of information that will help your fishing. This includes feedback on the fish size, underwater structure, as well as the type of bottom where you are fishing.

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All that you need to do is to know how to read the fish finder screen. In this section, we will provide tips on how to read a fish finder screen.

How Fish Finders Work

Before we discuss how to read a fish finder screen, it is important to explain how fish finders work. When you put a fish finder in the water, the bottom part known as the transducer emits sonar waves. These sonar waves move around the water before returning to the transducer.

The transducer notes the distance, rate, and speed at which the sonar waves return before converting this raw data to visual data for the angler. This visual typically takes the form of thick colored arches and lines.

There are three important pieces of information that you can get from a fish finder screen which are depth, water temperature, and speed.

1. Depth

To measure the depth of the water, most find finders come with a depth finder. Knowing the depth of the water in which you are fishing gives you a clear idea of the fish species that inhabit the area.

This will ensure that you use the right bait and an effective fishing technique. The depth is usually measured in meters, not feet.

2. Water Temperature

The water temperature is another essential reading that a fish finder provides. The temperature of the water body helps you to make informed decisions on fishing tactics and tackle.

This is because you can determine what fish species are present at a location, depending on if it is warm water or cold water.

3. Speed

The speed sensor is also important to your fishing, as it serves as a speedometer. It helps you to check how fast you are moving in the water in order to get the right presentation.

Types of Images

There are two classes of imaging when it comes to using a fish finder. They are fish icon and fish arch. In this section, we will explain what both types of images mean, as well as highlight their differences.

1. Fish Icon

Fish finders that display results in the form of fish icons are powered by Fish ID technology. A fish icon is a user-friendly display that converts the results from sonar waves into little images of fish.

These images are represented in different sizes and lengths, showing the sizes of fish that the fish finder has picked up. In this way, the fish finder ensures you are fishing in the right environment. It does not end there.

A fish finder that runs on Fish ID technology also displays schools of fish, rocks, and vegetation. This can be found in the depth of the display. One downside to the use of Fish ID is that your fish finder might perceive rocks or plants as schools of fish.

2. Fish Arch

Fish finders that display visual data as fish arches are called arch fish finders. These fish finders represent everything in the water as arches. This includes fish, grass, rocks, logs as well as other objects.

Fish arches usually reflect in colors based on the echo return strength. You might wonder how it is possible to differentiate a fish from logs or grass. We will discuss that below.

Determining Fish Size

Judging the size of a fish is quite simple and straightforward when using Fish ID technology. This is because the finder displays the fish as icons in the right proportion, depending on size. However, with an arch fish finder, you have to know to read the arches.

The best way to do this is to measure the arch horizontally and vertically in order to get the thickness of the fish. With time, you will have no trouble determining the size of the fish.

Fish arch length and fish arch width also factor in when judging the size of a fish. The length of a fish arch indicates the location and movement rather than the length of the fist.

The width is a better indication of the size of a fish. It shows you how big the fish is, be it through sidescan or downscan.

As a rule of thumb, the thicker the arch on the fish finder screen, the bigger the size of the fish. The fish arch width can help you to determine the best presentation.

A short and thick arch usually indicates a lethargic fish, so a slow presentation might be best. Longer arches usually indicate an active fish, which will require a faster presentation.

Detecting Bait Schools and Fish

Telling a school of baitfish from larger fish might be a bit tricky. However, there are tips on how to differentiate them. Baitfish usually appear like dots, dashes, and lines on an arch fish finder.

As baitfish move in schools, these dots and dashes are likely to form a blob. There are certain factors that can help you tell a bait school apart from vegetation or big fish.

One major factor is the color, as the arches of most baitfish are colored yellow. A school of baitfish also typically resembles a cluster on the screen.

You can also tell a baitfish school from vegetation by its location. Baitfish are typically suspended in the water, while vegetation is at the bottom.

For bigger fish, on the other hand, the width of the arch tells the full story. A thick arch is an indicator of trophy fish such as largemouth bass or pike.

Finding Fish Hidden In Structure

Just like it is on land, different structures exist in the water. These structures include vegetation, weed bed, depressions, points, and other objects.

In this section, we will discuss the identification of structures using a fish finder.


Depressions are important structures when it comes to fishing. This is because bottom feeders such as catfish and carp can be found in these structures. To identify a depression, look out for v-shaped changes at the bottom of the display. These changes can be found in the contour of the bottom of the water.

Other Objects

Other objects in the water include items like cars, sunken ships as well as old nets. Fish use these items as hiding places in the water. To find this structure, you need to look out for sudden points or dips in the contour at the bottom.

Finding Fish In Weed Beds With Sonar

It is no news that fish enjoy hiding within weed beds and vegetation. Look out for vertical lines and spottier returns on the screen when looking out for weed beds. Larger fish are commonly found in areas with plenty of vertical lines.

Traditional Sonar, Downscan, and Sidescan

Downscan and sidescan are two types of sonar imaging on fish finders. Downscan provides down imaging while a sidescan provides side imaging.

Down Imaging

Down imaging is typically associated with traditional sonar. With down imaging, the transducer of the fish finder sends the sonar wave down to the bottom of the water, and it bounces back up to produce the fish arches.

In doing this, the fish finder does not cover the sides of the water, thereby providing the angler with limited information. Down imaging is a reliable method of identifying the structures and bottom of the water body.

Side Imaging

Side imaging involves sending the sonar waves sideways into the water. Side imaging produces great images and gives the angler a clear idea of where the fish is located.

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Technology has made fishing easier, and you no longer have to leave everything to chance. Using a fish finder, you can fish better, faster, and much easier without having to stress.

Once you learn how a fish finder works using the guide above, you will be sure to have an enjoyable fishing trip.

Daniel O’Neill
Fishing Expert
Daniel specializes in fly, predator, and saltwater angling. He has practiced angling from a young age, quickly developing his knowledge of fishing fundamentals. His angling journey began in Ireland, primarily targeting rainbow trout on a fly rod. His passion for angling grew extensively as he ventured into other forms of fishing. He primarily targets freshwater and saltwater destinations in Ireland and the UK. His favorite catch to date was a 7lb / 3.6KG thick-lipped mullet from the Northern Irish coast—a prized fish to target on a fly rod. He is now the owner of DON Angling, a business that intends to inform and educate anglers on the best techniques, methods, and etiquette available.
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