How To Read a Fish Finder: What Every Anglers Should Know

We all know how useful a fish finder can be when it comes to fishing. Despite the fact that this device is becoming more popular, not many people know how to use it properly. Thus, in this piece of writing, you will find out a complete beginner walkthrough on how to read a fish finder.

Even if you have not owned a fish finder for yourself, knowing how to read it is still necessary. It helps you to get familiar and manipulate your device faster when you buy it in the future.

how to read a fish finder

How To Read a Fish Finder in 5 Steps

1. Know where the fishes are

The first must-know thing when reading the fish finder is the mechanism of sonar. The transducer in your fish finder emits the sonar waves. These waves bounce and return to the transducer.

The transducer will then interpret the data showing you the depth, speed, distance, and frequency at which the waves come back. Based on these raw data, you can tell where the fishes are.

Depth finder

With this feature, you will know how deep is it from your vessel to the bottom of the lake. This number is normally shown on the left on the screen. And more than often you will see it in meter unit instead of feet.

Temperature sensor

Some types of fish prefer warm water, some others prefer cold. You will see the temperature right below the depth. Just using these two features is sometimes enough for looking for fishes.

Speed sensor

This feature telling how fast your vessel is moving. You can thus set up a better angler and become more experience in locating your catches.

2. Estimate the sizes

When they sonar waves return to the transducer, you can choose to see the raw data or make it more understandable by seeing them in icons. And people call it the Fish ID technology.

Specifically, you will see the fish icons of different sizes. The size, of course, tells you how big or how small the fish is.

When you turn off the Fish ID feature, you will then see the arches.

Arch length

A longer arch does not mean a bigger fish. Long arches tell you that the fish beneath is small and stationary or slowly moving.

Arch width

The wider the arch is, the bigger the fish seems to be. In other words, think vertically, not horizontally.

Half or full

The fact is, half or full arch does not indicate whether it is a big or small catch. Instead, you just need to notice the width when considering its size.

The reason is that full arch shows that the fish swims through the whole of the sonar cone. Half arch shows the opposite.

3. Predict the underwater structure

There are two important notes for identifying the water structure.

First, the transducer scans constantly. The sonar display keeps scrolling even when the sonar is stationary.

Second, the depth scale helps you to know the depth of any feature. It shows you the bottom depth under the fish finder. Thus, it may not be the same depth as the feature you just scanned.

underwater structure fish finder

To increase the accuracy of sonar interpretation, here are 5 tips for you

  • Maintain steady speed
  • As you find a good spot, use narrow sonar to get more details of the structure
  • When you are marking the structure, don’t pay attention to the arches
  • In a large area, you should set a depth alarm. It will tell you when you get to your chosen depth area.
  • Small depressions can be ideal features for your catch, especially when you are fishing for carps

4. Judge the bottom type

Knowing the bottom type and harness is also an important key in reading the fish finder and maximizing its functions.

The sonar waves will come with different intensity when they hit different bottom types. As the rule of thumb, the more vibrant and contrast the color you see, the harder the bottom seems to be. Specifically, the color can range from brown (soft) to orange (hard).

Additionally, hard bottoms will send strong returns. When you see the second sonar return which is parallel to the line at the bottom, you can tell that the bottom is hard.

Another clue to know the hardness of the bottom is the thickness of the lines. The thicker the lines are, the harder the bottom is.

For soft bottoms, you will see many gaps and dashes on the lines. And if the lines are long, they indicate sand, silt or mud. Otherwise, they are gravel or stones.

5. Read the data display

As the colors, echo returns, shapes are easy for you to understand, you should know how to interpret the results. First, for best accuracy, set up your fish finder and move slowly around. Most fish finders work best at a lower speed.

Unlike reading an English book, you need to read the display from the right to the left. Most recent results will show up from the far right, and vice versa for the oldest results.

fish finder data display

When reading the fish finder, you should get familiar with the distance and the proportion from your vessel to the device.

As you already have an interesting spot, it is time to zoom on that spot to have a detailed image of what it is like underneath your vessel.


Knowing how to read a fish finder should not be something too complicated. As you spend your time and effort in learning how it works, your fishing trip will be much easier and more enjoyable.

And more than just helping you to locate your catches, a fish finder is a helpful tool for navigating your way on the lake. It provides you with the necessary knowledge of water temperature, depth, and structure.

Hopefully, this piece of writing is useful. Wish you all the best in your learning.

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