How To Read And Use A Fish Finder

Have you ever spent hours paddling around in search of fish only to end the day without a catch? You can’t force a fish to bite, but you can increase your chances of success if you use a fishfinder. Fishfinders are portable, relatively inexpensive and immensely valuable. But many people who invest in this technology don’t know how to read a fishfinder properly.

Learning how to read a fishfinder before you get out on the water will reduce frustration and ensure that you put your money to good use. If you want some recommendations, this page reviews some of the best fish finders out there.

How Do Fishfinders Work?  

Fishfinders are small computers that use SONAR to show objects underneath and around the boat. Many are also equipped with GPS.

The transducer is the part of the fishfinder that sits in the water. It is usually found on the flattest part of the hull in a kayak.

SONAR of shipwreck
By Tuukritööde OÜ (Muinsuskaitseamet) [CC BY-SA 4.0 (], via Wikimedia Commons
The transducer is akin to the eyes of the fishfinder. It has elements that vibrate, sending electronic pulses through the water. These pulses bounce off of objects and make their way back to the receiver.

The software analyzes the time that the signal took to return as well as its strength. It transforms this data into an image on the screen.

The image isn’t always straightforward, though. It may appear as vague, colorful blobs, lines or arches. If you don’t know what you’re looking at, you won’t be able to use the technology effectively to find fish. We’ll discuss how to read a fishfinder in more detail later in this article.

Understanding Sonar

Sonar extends its frequencies in a cone shape. A 200 kHz sonar beam has a wider cone than an 83 kHz one. It will cover a larger area, but it will contain less detail.

How To Install A Fishfinder

A small unit is usually ideal for a small boat. You can install a fishfinder on a powerboat, a kayak or any vessel.

Some angling kayaks come with fishfinders. Others don’t, but they may have a mounting point that’s designed for a transducer so that you don’t have to drill blindly into the hull. Here is a video showing an example of how to install a fishfinder on a kayak:

If you’re concerned about installing a fishfinder permanently or semi-permanently, you can find an option with a floating or over-the-side transducer. This type of fishfinder is especially perfect for using with a fold-up or inflatable kayak.

Some transducers can be cast. This is helpful when you’re navigating waters slowly in a kayak. You can cast the transducer several feet away from you to investigate a certain spot.

Installing a fishfinder on a large boat usually involves attaching it below the hull. However, most kayaks are thin enough that you can place the transducer on the inside of the hull. This may eliminate the need to drill holes in the boat.

No matter how you install the fishfinder on your boat, you should make sure that it’s easy to remove for transport and storage so that it doesn’t get damaged.

How To Read A Fishfinder

Every fishfinder is different. Some come with monitors that display the data from the transducer. Others communicate directly with your smartphone via Wi-Fi or Bluetooth.

Extra Features

Most fishfinders have the following features:

  • Depth finder
  • Water temperature sensor
  • Speed sensor

Understanding the depth and temperature of the water can help you know what kind of fish you might find in an area.

The depth sensor can help you scout out new areas. If you have the type of transducer that can be cast, you can check out those spots without scaring away the fish by paddling your boat into the region.

The depth is usually displayed on the top left of the screen in meters or feet. The accuracy depends on the model of the specific fish finder that you use.

The water temperature is usually displayed below the depth reading. Knowing the water temperature can also help you determine what fish may be present in a certain location. Paying attention to this data can help you understand what to look for as you become a more experienced angler.

A speed sensor can help you plan out kayaking trips and time your fishing excursions. It’s especially helpful if you’re planning to hit up a new location but aren’t sure how much time to give yourself.

Fishfinding Features

You’re probably in the market for a fishfinder because you actually want to locate some fish. Let’s talk about the readings that will help you impress your friends when you return to shore.

The thickness and color of the lines and blobs can tell you a lot about what’s underneath you. The bed of the body of water that you’re traveling in will appear at the bottom of your screen. A thicker line indicates a harder, less porous surface. A think line might mean that you’re traveling over clay.

If you’re using a fishfinder with 2D sonar and a color screen, a hard bottom will usually appear as a yellow band with blue below it. A mucky bottom won’t have the defined bands and might look orange, depending on your device’s color palette.

This information is relevant to your fishing experience. The more you know about each environment, the better you’ll be able to understand where the action is.

At the top of the screen, you’ll see surface clutter. This is created by water disturbance around the transducer from your boat, your paddle or waves.

The fish show up as blobs, arches or clouds in between the water surface and the ground. You should be able to detect the difference between individual fish and schools. Larger fish might have a colored spot in the middle because they reflect a strong sonar signal.

The display on the screen moves as you do. The picture will remain more stable the slower you go. The newest information is shown on the right. The part of the display that shows up to the left is the older information.

If you want to know what’s directly under your boat, direct your attention to the right side of your screen. The data to the left shows what you’ve passed over previously.

Some fish finders transform the raw data into icons that help you distinguish between fish and other objects below the water surface. Others simply show you the lines and arches, leaving you to decipher their meaning.

Fish-ID Technology

Devices with fish-ID technology use an algorithm to analyze the data for you and give a clear representation of where the fish might be. Many people find this interface to be more user-friendly than one that shows raw data.

Some fishfinders with this technology also have icons for plants, rocks and schools of fish. The measurements on the sides of the screen will show you the depths of these objects. Being able to read this information will help you understand where to cast your line.

The downside of fish-ID technology is that it is not always 100% accurate. You’re relying on a computer to decipher the difference between a group of plants and school of fish.

You might become dependent on seeing the icons without using your own analytical skill to determine whether the objects in view are fish or something else. Fish-ID technology is associated with a high rate of false positives.

While some people feel like fish-ID technology is a gimmick, this feature can come in handy in certain instances, such as detecting fish within brush or another type of cover. The color image will show a submerged tree or weeds as a mass of jumbled color. It should show fish icons as well if any fish are hiding in the brush.

Arch Fish Finders

It can take some time to learn how to use an arch fish finder. Once you have developed the skill, however, reading the screen will become second nature. It’s kind of like learning to read in a new language.

Arch fish finders show the data in the way that it’s transmitted to the transducer. An object that’s not moving will show up as a straight line. A moving object will appear as an arch. Therefore, a fish will materialize as an arch on the screen.

The size of the lines and arches corresponds with the size of the object. Bigger arches indicate larger fish. Sometimes, you’ll see half arches. This means that the fish didn’t pass through the center of the transducer cone. Fish that hug the ground might show up as fluctuating arches.

How to read a fishfinder might make sense on paper, but deciphering the display might be more challenging in practice. Take your time to learn what the different marks on the screen represent. You’ll become more adept at using the device the more you use it.

Combination Fishfinders

Some fishfinders let you swap modes and view either the fish icons or the raw data. If you switch back and forth, you might notice that the fish-ID mode shows you lots of fish, but the arch/line mode shows few arches.

This is an example of the unreliable nature of fish-ID technology. If you’re moving over plant life, it might show up as separate fish icons.

One way to determine whether they’re fish is to notice their placement. Fish icons that appear to be stacked vertically are likely to be plants. If the fish icons appear to be connected to the surface of the ground, they’re probably plants.

Single Vs. Dual Frequency

A single frequency fishfinder sends out one cone of sonar. A dual frequency fishfinder gives you the data from two cones at once. The high-frequency cone in the center delivers more detail, while the lower frequency cone tells you what’s around it.

The information might display on a split screen. If you have fishfinder technology, the fish within the high-frequency cone will be blue, and the fish in the low-frequency cone will be orange. They may look like they’re hanging out together on the screen, but the orange fish are really the ones around the boat. The blue ones are the ones that are directly underneath you.

Side Imaging

Side imaging can be confusing to analyze on a fishfinder. For starters, your transducer has to be installed properly and in the right location. The transducer must lie below the hull and have a clear range from side to side.

Like other types of fishfinders, those with side imaging usually use different frequencies. The 800 kHz option will give you the sharpest images, and the 455 kHz option will give you the widest range.

Read the information in side-imaging mode from top to bottom. The newest details are on top, while the older areas are on the bottom.

Tips For Reading A Fishfinder

When you’re learning to use your fishfinder, it can be tempting to want to fiddle with the colors, contrast and other variables right away. You might also get excited to find fish and drop a line immediately.

The best way to get comfortable with your device, however, is to read the manual. All fishfinders are a little different. Even if you’ve read dozens of articles online, you need to understand how to use your specific model.

man reading sign

Next, use it while traveling slowly in an area with which you’re familiar. Get a sense of what different objects look like. For example, paddle past some pilings and check out what they look like on the screen. If you know of an area that’s often rich with fish, travel there and spend some time making out the animals on the display.

Once you have become a little more familiar with the device, you can adjust the settings. Change the color palette so that you can read the display easily. Adjust the update speed to show you data in real time without getting overwhelmed by the speed at which the information is presented. Play with the transducer’s sensitivity if you’re getting inaccurate readings.

As you learn more about your fishfinder, it will help you become a better angler. Understanding the different data allows you to get a better sense of the environment so that you catch a fish every time.

Tight lines!