How Does a Fish Finder Work? All You Need to Know

Before knowing how does a fish finder work lets know what is the definition of fish finder and what types of fish finder are available in the market today.

A fish finder is a device made to view the presence of fish bellow the water that also help to measure the depth of water.

It also reveals all underwater objects including rocks, wreckage as well as school of fish that our eyes can not see openly.

Every year various types of new innovative fishing accessories are coming to the market keeping in mind the need of users.
Manufacturers are literally designing these amazing new devices to survive in the competitive market.

Types of Fish finders:

No matter what is the type of fish finder. When it comes to fish finders every device is designed to do same tasks. Measuring the depth of water, get a graphical view of all the underneath composition and the bottom structure of the water from any angle.

When the early model of fish finder invented more than 60 years ago, it came with only few basic options- a power switch, range selector and a sensitivity adjustment feature.

But today, differences on all fish finders units are many – screen size, color, combo vs standalone, pixel, power, frequency etc.

Two Basic Parts of Fish Finder:

A fish finder consists 2 parts-a transducer and display. These two units are correlated with transmitter and receiver.

Transducer is the ears of your fish finder where display is like your third eye to locate fish under water.


Transducer is attached  either on the transom outside of the boat , through the hull/in hull, or on the trolling motor mounted in the water.

It works like sonar technology which recognizes objects using electric signals and then show size and distance data to display unit by art like graphics.

How fish finder transducer works
Function of Transducer Under Boat

An electrical wave is created from transducer and passed through water by transmitter.

When this wave is interrupted by an object it bounce back to the computer part or display unit.

When the sound wave hit any objects it account the shape, size and altitude of the object. Then a graphical spectacle is back to the display.

The exact length and weight  it can ascertain of underwater fairly depends on the power and frequency of the device.

The distance of the object from the transducer can be determined by accounting time interval between transmitted wave and received signal in the display.

Constant speed of seawater wave is determined 1500 meter per second and 1463 meter per second in freshwater to read the speed of wave.


The display is the most important part of a fish finder device.

It show all information including graphics, water depth, temperature, speed over water, bottom shape and types and fish location etc. The users have full control how he want to operate the device by using menu system.

How fish finder display works
Basic Function of a Germin 160C Display

One main feature in the display is sensitivity setting. By synthesizing the sensitivity of the unit you will be able to adjust the power.

Less the power of sensitivity, the less attribute of the image in the display.
Different displays has different resolutions and colors. It can be gray or color or black & White. Better the pixels of colors, better quality image it can show.

How Fish Are Detected?

Within turn off the fish ID landmark you can learn to differentiate fish from rocks, vegetation and other objects. Fish will look like an arch on the screen automatically.
The reason is, the space between the fish and the transducer is innovated as fish swims or boat change its location.How fish finder display works

Here are some basic steps how to read a fish finder  and how does a fish finder work when detecting fish: When a fish  comes into the beam, it indicate a small mark on the screen.When the fish enters into the center of the beam the center of the arches become curve up.When Fish exit from the beam, the distance incremented and mark become curve downward.

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