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How to Read a Fish Finder: 6 Effective Tips for Reading a Fishfinder

how to read a fish finder
Written by Immanuel Baranov
Last Update: July 24, 2023

How will you feel knowing if you know the exact location to find the fishes you need? Finding fishes in large number to increase your chances of a successful catch? Everyone will love this right? Yes, this is what you’ll if you learn how to read fish finder.

As the name implies, a fish finder is a piece of valuable and portable equipment that allows you to know where a school of fish are in the water. It also helps you to know the condition of the bottom of the water.

You can walk in any fish store and ask for a high-end fish finder. But you’ll be wasting your money if you don’t know how to read a fish finder. This article contains everything you’ll need for reading a fishfinder.

How to Read a Fish Finder?

Every fishfinder comes with its unique features. You’ll find some with screens that display the signal from the transducer. Some can communicate with your Android and iOS devices through Bluetooth or Wi-fi. But knowing how a fish finder works is a right step to understanding how to read a fishfinder.

How Do Fish Finders Work?

How to Read a Fish Finder

First, what is a fish finder?

A fish finder is an electronic device that uses the technology of ‘sonar’ to show objects that are under the boat. Some of the best fish finders on the market come with GPS devices to enhance its accuracy.

One of the most important components of the fish finder is the transducer. It is the part of the fish finder that has direct contact with the water. The transducer is often positioned at the lowest part of the boat. We can say that the transducer is the eye of the fish finder.

So, how does the transducer work?

The transducer sends an electronic pulse into the water. If the pulse encounters an object, it’ll quickly return to the receiver. The time it takes the signal to return and its strength determines the type of object. Besides, there is a software that analyses the signal received and transforms it into an image.

The image that appears on the screen is not very clear. You might see some lines, arches or colorful blobs. You can only find the fish if you know how to read sonar fish finders screen.

The Art of Reading a Fish Finder

Every art is a skill which is learned. Since reading a fish finder screen is an art, here are a few steps that will help you.

1. Identifying Fish

Identifying Fish

Your aim of getting a fish finder is to enhance your success at the catch. But how will you catch the fish if you can’t even identify it? This is where identifying the fish is very important. The screen of the fish finder is usually a friendly interface that helps you to see what’s underneath your boat.

Fish Icons

Fish finder comes with a fish-ID that helps you to locate those fish icons. These icons are in different shapes and lengths. With this, it’s easy to differentiate a fish from plant or rock. You’ll need to identify the icon on the screen as well as its depth.

Also, should be patient when learning how to read sonar fish finder via fish icons. This is because what is displayed as a fish might be some plants. Yet, you’ll need constant practice to master the methods of using fish finder.

Fish Arches

Most fishfinders will display the signals from the transducer in arches and lines. You’ll be saving much time if you understand how this works. You’ll notice that images in the form of arches are clearer and easy to read than fish IDs. For example, if a big arch is displayed on the screen, it means there is a big fish below. Also, a small fish arch means the fish underneath or around the boat is small.

Sometimes you’ll experience some difficulty trying to differentiate a fish from a rock or plant. Don’t worry, keep practicing. Soon, you’ll master the arts.

2. Judging Fish Size

So far, we’ve said that what you see on the screen is the same size as what’s below. But, this isn’t always true. You’ll need to make further analysis of the displayed arches. This you’ll do by checking the length, width, and the ache’s thickness.

Fish Arch Length

You’ll be making a mistake if you believe that a long fish arch means a big fish. Rather, it’s best to measure the length of the arch as time. What does this mean? It means what you see on the screen is proportional with your position to the fishes. For example, you’ll likely see a continuous line if your fish finder encounters a motionless fish. Note that the fish could be either be big or small.

If your transducer picks two fishes underneath and they’re moving at a different speed. The fish with a slower movement will have a long line while a short line indicates the fish that is moving fast. Here, the sizes of the fish do not apply. So, the long fish arch does not mean big fish.

Fish Arch Width

Since arch length fails to show how big the fish is, what about the arch’s width? As a rule of thumb, always consider the vertical not horizontal when reading the screen of a side imaging or bottom imaging fish finder. Irrespective of the length of the arch, if it’s thick, then the fish is big. Always know that the thicker the arch, the bigger the fish.

 Half or Full Fish Arches

You’ll either have a half or full arches on the screen. So, how do you read a fish finder with a half or full arch? If the fish is swimming in the cone of the sonar, then you’ll see a full arch. Also, you’ll see a half arch when the fish gets to a section of the cone of the sonar.

Besides, if the arch is half, it does not mean small fish neither does a full arch mean big fish. As we mentioned earlier, the best trick to know fish’s size is to pay attention to the width of arch.

3. Finding Bait Fish and Trophy Fish on Your Fish Finder

Most fish finders will either display dots, lines, or dashes as a baitfish. These fishes are often groups in the water. Using the thickness of the arch is often the best way to identify a trophy fish.

4. Identifying Different Types of Underwater Structure

Identifying Different Types of Underwater Structure

Learning how to read fish finders will help you to know the depth of the bottom and other structures in the water. This is when you need the depth feature on the transducer. This feature allows you to determine how deep the water is. Besides, it gives you a clue of the fishes that would be at such depths.

You’ll find the depth feature at the top corner of the display. Its unit of measurement is meters. You may need to convert it to your preferred unit of measurement. Besides, you’ll need to troll or reel your finder at slow speed to see the contour of the bottom clearly. This is how you’ll identify drop-offs.

Once you’ve gotten your drop-off, try to scan the area again with a slimmer beam. This is to enhance your confidence in the picture you’ve obtained. Besides, it’ll help you to avoid dead zone areas during the scan. You can set a depth alarm if you’re paddling in a large area. Here, you’ll receive an alert once you’re within your chosen depth.

You can identify a brush or log from the color of your display. Since each structure sends a different frequency to your sonar, their colors are not the same. You’ll need to choose the right color palette.

Vegetation and Weeds

Sometimes you’ll like to fish in areas with plants and vegetation. Your fish finder will display vertical lines or spotter return for vegetation.


If you’re into carp fishing, you’ll likely target depressions. You should know that fishes create these depressions. A small v-shape dip at the bottom, while you’re strolling or reeling will state a depression.


You’ll need to take your time to spot the points even though it’s not very difficult. It’s important to maintain your speed of troll or reel to get accurate results. You might start the scanning with a wide beam then switch to a narrow beam to pick all the shelves and humps.

Other Underground Objects

It’s possible for you to discover a car underneath your boat through your fish finder. You can use the shape and strength of the return signal to determine the object below. If it’s a very hard object, you’ll observe the repetition of the return signal.

Using the Fish Finder to Know the Bottom Type and Hardness

In spite of the type of fish on your mind, it’s important to know how hard the bottom is. Below are the factors you should consider when trying to crack the code.

1. Thickness

You can have a clue of bottom via the thickness of the line on the screen. The rule is simple; hard bottom produces thicker lines. So, a thin line on the display indicates a soft bottom. But, sometimes the sensitivity of your sonar can influence the thickness of the line. It’s important you know how to adjust the sensitivity of your sonar.

2. Color

The intensity of the signal from a soft bottom is different from that of a hard bottom. You can set a color palette to identify this. If the echo is strong, the color on the display is dark. This is often useful in fish finder models with color palette modes.

3. Second Returns

Hard surfaces will produce strong returns that will bounce and return again. It will show on your screen as a 2nd return sonar. It is parallel to and under the line showing the bottom.

Tips for Reading a Fish Finder

  • Be careful to read the manuals and follow the instructions from the manufacturer.
  • Try to understand the model you’re using by practising with it.
  • Use it first in an area you’re familiar with. Try to figure out how some identified objects appear on the screen.
  • If you’re familiar with your model, you can go ahead to adjust the settings.
  • Change the color palette to suit your interest.
  • Adjust the sensitivity of the transducers as well as the update speed. This will help you to get timely and accurate readings.


You’ll become a better angler now that you know how to read fish finder. No matter what if you are using a fishing drone or a fish finder, you can only have a better view of your environment if you understand the data on your screen. So, instead of wasting your day searching for a catch, get a good fish finder and tell a better story.

About the author

Immanuel Baranov

My life is pretty much defined by my avid outdoor activities. I’m generally obsessed with fishing, skiing and occasional hunting and whitewater paddling. I’ve been active since my early years. I inherited my passion for fishing from my father who made frequent family trips to the banks of Sacramento River. Growing up, I did a lot of fishing in the vicinity. Now that I have two sons, our weekends are full of fishing activities. I would say, you need good spots where you can go out a lot for the thing you love. I had the privilege to grow up near numerous water bodies and I’m proud to say that I made good use of them. It’s also great to do something with kids that helps them learn patience, endurance and preciseness.

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