How to Read a Fish Finder

fish finder viewing baitfish

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Look for fish icons and symbols that indicate bait fish and large individual fish of your target species that are swimming at a depth that your lure can dive to and cast in front of them.

Fish finders are among the most useful tools for anglers of all kinds, but they are often a mystery to beginners and novice anglers. It’s understandable for those who are new to fishing to ask questions related to fish finders, one of which everyone must consider at some point:

What can a fish finder see?

In this article, I will provide a brief and simple answer to this topic to give anglers more confidence in choosing whether or not to purchase one for themselves.

Fish Finder Overview 

If you’re new to the sport of fishing and you’re not quite sure what a fish finder is or what it does, you’re not alone. Put simply, a fish finder is an electronic device mounted to a boat that anglers use to detect fish below or around their vessel, as well as structure and depth. Over the last few decades, I have seen many different types of fish finders enter the fishing industry. These tools have proven to be revolutionary in every sense of the word when it comes to the sport of fishing. 

A fish finder is often not as straightforward as some anglers expect them to be in terms of the imagery and data produced by the device. Depending on what type of fish finder you use, fish might appear as a small crescent-shaped fish arch, a dot or even a fish icon on older models. Some more advanced fish finder models operate using a system that requires the angler to understand what it can pick up and how to decipher the images on the screen. 

Most fish finders operate using CHIRP sonar systems. This system stands for Compressed High Intensity Radar Pulse and is an improved version of 2D sonar that was first used in fish finders many years ago. The main difference between CHIRP sonar and traditional sonar is that the older technology uses a single beam while the CHIRP sonar works using continuous beams that provide a better overall reading. 

The different types of fish finders include:

humminbird helix 10

How Do Fish Finders Work?

Depending on the technology used in the device, fish finders are capable of rendering on-screen data using several methods. The following sections briefly explain the various types of fish finders and describe how they work. 

2D Sonar

The 2D sonar fish finder is the oldest version of this technology and has been in use for decades. These devices operate using a transducer placed on the boat’s bottom. The transducer projects a conical-shaped sonar signal downward into the water and yields an image of what’s beneath the boat on the screen. 

3D Fish Finder

A much newer version of fish finder technology, the 3D device operates using a side-imaging transducer along with specialized software to render a 3D image of the fish and structure along the bottom. The images are impressive, but many anglers like to rely on live sonar technology instead of 3D fish finders as they are better at helping you distinguish one object from another. 

Live Sonar

Live sonar has only just been released in recent years and works using the same basic sonar system but with more advanced software that provides continuously updated readings that look very much like you’re watching a live-stream video of what’s happening below you’re boat. 

How to Read a Fish Finder 3

Down Imaging

Down imaging is widely considered a staple among professional anglers and fishing guides because it’s one of the most reliable forms of technology in the fish finder industry. Down imaging uses a thinner, more sensitive sonar band downward into the water. The results are more crisp and accurate images that can be read at greater depths, hundreds of feet into the water. 

What is Down Imaging

Side Imaging

Side imaging utilizes two sonar cones sent out on your boat’s left and right using a very sensitive and accurate detection method. Most professional anglers will use side and down imaging at the same time when scouting a lake before a competition, as well as during tournaments. 

Side Imaging

360 Imaging

360 imaging is virtually identical to side imaging, except it utilizes a transducer that constantly rotates and produces images in every direction that are crystal clear and accurate. As you might expect, 360 imaging is often very expensive. 

mega 360 fish finding technology


A chartplotter system is a device that combines sonar readings with a map feature which is often connected to a GPS unit. This device is mainly intended to read the boat’s position and provides a clear indication of the best course you should take and is much more useful on large lakes and reservoirs, as well as for offshore fishing. 

What Can a Fish Finder See? 

Now that you have a basic understanding of how most fish finders work, you can more easily grasp how this technology operates and what you might expect it to pick up. Since most fish finders work using one or more beams of sonar, these beams will usually pick up everything solid in the water. In the following sections, we’ll explain in greater detail how a fish finder reads some of the most common things you find in the water. 

How Does a Fish Finder Read Fish? 

A fish finder will indicate fish using a small fish icon or a fish arch. Since most fish are moving and their body shape is curved, the sonar signal will produce an outline of the top of the fish, which will appear as an arch on most modern fish finders. You can usually tell how big a fish is by the thickness of the arch, as well as the length. 

This fish arch might be longer in some instances if the fish is moving while the sonar is pulsating and reading the water. This will produce a thin, long arch that some anglers mistake as being a large fish. Experienced anglers know that you can tell when your fish finder has picked up a large fish as it will show up as a very thick arch.  

How Does a Fish Finder Read Bait Fish? 

Shad and other types of bait fish are an integral part of the fish ecosystem and virtually all specimens of game fish feed on them throughout the year. Fish finders can read schools of bait fish and shad with most of them producing an image that looks like a cloud or splotch on the screen. 

In some cases, it may be hard to distinguish a school of shad from a brush pile underwater, but most fish finders will indicate one or the other using specific colors. One of the best ways to differentiate a school of shad from a brush pile is to view the space underneath the cloud on the screen. A school of bait fish, usually called a bait ball, will usually have a blank space underneath it between the cloud and the bottom. On the other hand, a brush pile will always be connected to the bottom. 

A fish finder showing baitfish

How to Identify Depth Changes and Structure

When your fish finder is reading a section of water, it should always provide a reading of what the bottom looks like. You can identify depth changes by paying attention to these readings and looking for sharp changes in the contours of the bottom of the body of water. The best way to learn how to be fully certain of the type of depth change you’re looking at mostly comes with lots of practice. 


As you begin to use your fish finder and are better acquainted with its capabilities, you should develop an understanding of what it’s able to read and how certain you can be in the readings it produces. Be sure to do plenty of research on your fish finder’s specific make and model as there are hundreds of different choices, and each one has its own strengths and weaknesses. 

All fishing gear and equipment will have a direct correlation between the product’s price and its quality. Fish finders are no different, so be ready to make a sizable investment to acquire a great one. The best way to learn what a fish finder can see is to practice and gain plenty of experience on the water.