How to Read a Fish Finder to Find Structure and Fish

Reading the long list of advanced features available on the latest fish finders, you might need a computer science degree just to turn on the machine. But the same engineering that makes these modern fishing accessories powerful tools, also makes them easy to use. Choosing the best type of sonar and knowing how to interpret fish marks from bait and hard structure from soft bottom has never been easier. With exciting innovations like side view and live view sonar, combined with the best traditional fish finder, the capabilities of the most advanced electronics are at your fingertips. With all this new technology, let our experts learn how to read a fish finder to find and structure fish.

What is the best type of sonar?

Over the past few years, fish finder technology has leaped into the future. In addition to reading fish and structure below the boat, the best fish finders see to the side and in front of the boat. 

Traditional sonar sends a cone-shaped signal from a transducer. The signal bounces off the bottom and returns to the transducer to display an image of fish and structure below the boat. A step up from traditional sonar, CHIRP emits two signals at different frequencies. Like stereo sound, the two signals provide a more detailed image of fish and structure.

Using a high frequency signal, downscan sonar captures a photo-like interpretation of structure and fish. Instead of colored blobs and scratches on a traditional sonar display, the downscan image shows details of wrecks, rock piles, and deadfalls. Use traditional sonar to find fish, then switch to downscan to investigate structure.

Side view sonar shoots a high-frequency signal to the side of the boat to capture fish and structure up to 200 feet away. Mark a target with the side view, then circle around and zero in on the mark.

The most recent advancement is live view sonar. Like a scene from 20,000 Leagues under the Sea, live view sonar uses a directional transducer to take video of fish swimming in front of the transducer. Live view uses a directional sonar to capture images 360 degrees around the boat.

At first, the technology behind these amazing tools seems complicated, but the biggest advancement in sonar is accessibility. Using the latest generation of fish finders is easy and a great piece of fishing equipment to have.

How to read a sonar to find fish

When the sonar signal bounces off a target, it returns the transducer with valuable information. Fish finder signals are so powerful that an angler can distinguish between bait and fish, or hard structure and soft bottom. 

To detect fish, the signal bounces off the fish’s air bladder. A high-power sonar has strong target separation. The user can see individual fish and schools of bait. The best sonar will even differentiate between bass and catfish or a school of menhaden or a school of anchovies. 

Each fish finder is different. After practice, users can interpret the image for information about the fish. On a traditional or CHIRP fish finder, large fish appear as an arch or streak. Bait schools look like a blob or cloud. Larger, tightly packed bait will be a blob, while smaller baitfish look like a cloud. With experience, an angler can tell a bass from a walleye and shad from shiners.

On a traditional or CHIRP fish finder, the color display provides important information. Each system has its own color palette. In general, lighter colors are softer returns, and darker colors represent dense targets. Hard bottom might be dark red while sand and mud show up as orange or yellow. Tight groups of big fish will be dark red, and scattered schools of small bait will show up in light green. The best fish finder will pick up fish swimming close to the bottom. Look for a lighter color line directly over the darker bottom line. 

The best fish finders offer several color palettes to meet the conditions and user preferences. For example, white background is easier to see in direct sunlight, and dark blue shows more detail in low light.

Side scan sonar picks up fish and bait on either side of the boat. These sonars use a monochrome display with lighter shades representing dense targets. The key to finding fish is looking for the shadow. The signal returns an image of the target, leaving a dark echo behind it. The shadow not only helps identify fish or bait, but shows how deep it’s swimming.

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How to read a fish finder for structure

In addition to finding fish and bait, a fish finder is a valuable tool to find rocks, sand, mud, aquatic grass, stumps, reefs, and shipwrecks. Learning to interpret the colors and shapes will allow you to read the bottom like an open book.

Understanding the color palette on your fish finder is key to interpreting the bottom. Darker red return is harder bottom while lighter blue or green could be sand or mud. Hard structures like a reef or wreck will appear as a darker red mark rising from the bottom. Clumps of grass are softer than the bottom, so they appear as a darker signal. 

Down view sonar presents a photo-like image of the structure below the boat. Reading the monochrome display, you can see slight variations in a rockpile or wreck and clumps of vegetation around solid tree stumps.

On a side view fish finder, the signal returns images of structure and the sonar shadow behind it. A longer shadow indicates structure higher off the bottom.

Not all fishing tips have to do with how to cast and what lure to use. Learning to interpret the signals and identify the best areas to fish in is also part of the fun.

Tune your sonar for optimal performance

Most fish finders are ready to use right out of the box. Install the transducer and connect it to the display unit. Then, run the power cable to the battery. Push the power button and go fishing.

However, there are some simple adjustments to get the most out of your fish finder. A traditional sonar sends out a cone-shaped signal that is wider at the bottom than at the transducer. The deeper the bottom, the wider the signal—resulting in a less detailed image.

The best fish finders have a dual signal to get the best return in deep or shallow water—a wider beam for shallow water and a narrow beam for the deep. Fish finders with a CHIRP transducer send two signals for a stereo view of fish and structure.

For side view sonar, a wider range will pick up fish and structure farther from the boat while reducing image clarity.

Adjust the scroll speed to match the boat speed. A faster scroll speed will pick up fish and structure in less detail at a higher boat speed. 

To pick up small targets in deep water, increase the signal gain. To detect fish swimming higher in the water, reduce the gain.

Another deep water trick is to use the fish finder in split screen mode. One side of the screen shows the entire water column while the other side zooms in on the bottom. 

The easiest adjustment is setting the screen color. For traditional and CHIRP sonar, choose a blue or white background depending on where you use the fish finder. White tends to look better in direct sunlight, while blue shows greater target separation in low light.

The best way to adjust a fish finder is to start with factory settings and then experiment with slight adjustments to meet the fishing conditions and your preferences.

A final word about how to read a fish finder

Never have anglers had so many fishing tools to see below the water. Traditional, CHIRP, side view, down view, and forward-seeing sonar provide a detailed image of fish and structure so anglers can find fish.

The biggest advancement in fish finder technology comes in the user interface. These systems are advanced but easy to access. Still, it takes practice and experience to interpret the display for the most accurate information. After a little practice, you’ll be finding fish like a pro.