How Does a Fish Finder Work?

Setting out to a fishing expedition requires putting together your fishing tackle properly for a fruitful catch. But, that is not the only thing you need to plan for, considering finding fish on its own is an expedition.

This is where fish finders come in. But, you have to understand how they work to utilize their full potential. And, since not all anglers are tech-savvy, there is a need to understand fish finder basics.

In this article, you will learn about fish finders, including how they function. At the end of the article, you will clearly understand how to apply one to your regular fishing excursions.

Key Takeaways

  • A fish finder is a valuable fishing tool that helps you find the location of fish underwater and the other parameters of the water environment.
  • Fish finders work by transmitting ultrasonic waves and receiving reflections of the environment underwater, including fish and other objects.
  • Fish finders have two main components; the main unit with the screen showing the information found and the transducer detecting the objects underwater.

What Is a Fish Finder?

A fish finder is a tool that utilizes SONAR technology to identify fish underwater. SONAR stands for Sound Navigation and Ranging, a technology that transmits ultrasonic waves underwater, receiving reflections of the objects found.

In addition to finding fish locations, this technology comes in handy to detect various underwater information such as the depth, distribution of fish, water temperature, and the condition of the sea bed [1].

Fish finders come in various designs, with some featuring GPS, marine radars, and compasses. Depending on the model you choose, you can enjoy additional functionality apart from locating fish underwater.

How Does A Fish Finder Work?

A fish finder comes fitted with a digital screen that displays a reflection of the objects seen. In simpler terms, once a fish finder captures reflections of fish and other things underwater, it shows how they are distributed on the small screen.

Here is how it works from start to finish [2].

There is a transmitter on the ship or boat that sends signals in the waves. The SONAR system then uses echoes from the objects underwater to reflect these to the transmitter. The transmitted waves are then recorded, and a signal is sent to the digital screen.

Now, the received signals can be false in the event of transmitting reflecting coral or stones. But, a fish finder can differentiate false and true signals to show where fish are located.

The echoes produced by fish are different from those from stones underwater; this is how the fish finder transmits only the correct ones. On this note, signals from fish are displayed with different symbols from those of other objects for easy differentiation.

Most fish finders show the presence of fish by displaying fish symbols on the digital screen. Sometimes this can change to arches on the screen, especially when the boat is cruising over an area crowded by fish.

Even so, the fish display is unique to ensure the person monitoring the fish finder identifies where they are precisely.

How Each Fish Finder Component Works

A fish finder has several components that work together to ensure optimal functionality. Below is a description of how each component works.


The transducer is designed to detect what is around and under the boat, sending the data to the head unit. The information is then passed through the software and painted onto the screen [3].

Transducers come in different sizes and shapes, but their function remains the same. They feature piezoelectric elements that vibrate at specific frequencies, emitting pulses of sound into the water.

These elements come in various shapes and sizes, depending on the frequencies. For example, traditional 2D sonar features round elements while imaging elements come in a rectangular shape.


Most fish finders come with GPS features enabling them to chart your position. Most current models use internal GPS receivers, but external receivers work fine to show the boat location even at slow speeds.

GPS is an essential feature in fish finders as it comes in handy for navigation, finding fish schools, and marking return points if needed later.


This is a significant component of a fish finder where you get all the information found underwater. Fish finder screens vary from as small as 3.5 inches wide to as large as 16 inches wide.

Choosing a bigger screen is recommended as long as you match that with the SONAR features you need. The larger the screen, the more information you will get and the easier it will be to read it all.

The screen’s pixel density also varies; therefore, all screens will not have the exact resolution. It is important to note that pixels go down with an increase in the screen’s size, which means the images you get are less crisp.


Do Fish Finders Find Fish?

Yes. Fish finders work exceptionally well in finding fish and other objects underwater. They use SONAR technology to transmit ultrasonic waves and receive the reflection of the sea bed. This shows the condition of the underwater environment, including fish and other objects.

Does a Fish Finder Have To Be In Water To Work?

The transducer, a significant component of the fish finder, needs to be underwater to work. It needs to be submerged into water to function well and transmit the information on the screen.

The Bottom Line

Fish finders are helpful and have been shown to work exceptionally well in finding fish underwater. With the high technology fish finders use, they transmit a reflection of the environment underwater, showing where fish are and ultimately contributing to fruitful expeditions.

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