How to read a fish finder

How to read a fish finder

Before we take a look at how to read a fish finder, we should first understand how it works. What follows is a brief description of how a fish finder works.

How it works

A fish finder relies on sonar waves for it to function. They are emitted from a transducer, which is located in the water. The transducer then reads the waves that have been reflected back as a result  of bouncing back from an object in the water.  For this data to be viable, the transducer then converts this raw data to visual data. The kind of visual data depends on the type of fish finder; some have colored displays whereas others are black and white. Of course we are going to take a look at this feature in detail much later on.

One other thing worth noting is, the accuracy of a fish finder relies on the frequency and power of the waves transmitted. In other words, for the reading to be easier to the fisherman and more reliable, the frequency should be  strong enough.

What you expect to see on a fish finder screen

There are a number of readings you will find on the screen. Each reading represents a measurement of a component related to the body of water you are in. These readings help in getting the general idea of the environment under water. These readings are as follows;


This is made possible by a feature known as a depth finder. It is located on the transducer. This tells  the fisherman how deep the water below the vessel is. This is normally indicated on the top left of the screen and is usually measured in meters.

Water temperature

The reading is located directly below the reading of depth. This comes in handy when you want to locate some specific species of fish on the basis of the temperature in the water. Some species of fish prefer warm water whereas others prefer a cooler environment.


This is as a result of a speed sensor located in the fish finder. Its role is to tell the user how fast a vessel is moving. It is more like a speedometer and the results are also found on the fish finder’s screen.

How to read fish finder results

This depends on the type of fish finder you are using. As mentioned earlier, there are different  types of fish finders available. They can be classified either on the basis of the color of the display, or the technology they use in detecting the fish.

On the basis of color, there are two types; those with a colored display and those with black and white display. Regardless of whether the display is colored or not, the same principle is used to read and interpret the results. The results are read using the lines, the darker the lines, the stronger the echo. This means that if you see a thick dark line on your screen, then it shows that a hard, possibly large object has been detected. If the screen shows a thin light line, then it shows that something soft has been detected.

These lines also help fishermen to get an idea of the kind of seabed or ocean floor they are dealing with. The principle is still the same, a thick bold line represents a hard ocean floor and a thin line represents a soft material at the bottom of the sea or ocean. These little details matter, especially if one wants to understand the kind of fish and the type of the environment they can be found in.

On the basis of the technology used, there can be two kinds; those that use Fish ID technology and those that use Archs.

 Fish ID Technology

Some fish finders utilize this kind of technology which converts raw data to user friendly interface. This technology has the capability of representing different objects with icons that resemble their shape and size. Depending on your fish finder and how sophisticated it is, it may show different icons for different types of objects found under water. This helps in distinguishing fish from rocks, rocks from plants, and so on.

Once an icon appears on screen, read the depth, and then go ahead with your fishing. Then again, there are some fish finders, with this technology, that are found wanting when it comes to accuracy. One good thing about this kind of fish finders, they are suitable for amateurs and do not require much learning to understand how to read them. To sum it up, this technology makes it easier to discern various objects in the water, if that is what you are looking for.

Arch Fish finders

This type of display shows only raw data. It is difficult to interpret, but once you learn, it is the best. They are known to be more accurate and much better in general. If stationary objects are detected, it will be represented by a line, whereas a moving object is represented by an arch. It may be difficult to discern various moving objects using this type of fish finder.

However, it is highly recommended that you take some time to learn how to use it before you go to fish. It becomes easier operating it with time.


A few points to remember as I conclude; the results are usually displayed from right to left, starting with the most recent appearing on the right and the oldest on the left. Another thing is, it is imperative to ensure your vessel is as stable as possible. This will help in getting an accurate reading.

Last but not least, for your readings to become a bit clearer, it is advisable to familiarize yourself with the distance and other proportions from vessel to fish finder. Make use of additional features such as the focus, zoom feature, if you wish to take a closer look at a particular area for a more accurate reading.

So now you know how to read a fish finder, get yourself a fish finder that suits you and happy fishing!


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Paul Dudley

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