How To Read Fish Finder: A Beginner’s Guide to Understanding Fish Finder Displays

Fish Finder Guides

Learning to read a fish finder is not as difficult as it may seem. In fact, with a little practice, you can read your fish finder like a pro in no time.

The first step is to know what is a fish finder and how it works. The next step is interpreting the sonar images. Once you know how to read a fish finder, you can use it to locate schools of fish, identify underwater structures, and even drop your bait or lure in the right spot to increase your chances of a successful catch.

How to Read 2D Sonar

2D Sonar image

2D Sonar is composed of different colors to indicate the fish and structures below the boat. The colors represent the intensity of the echo returning to the transducer. The following is a guide to help you understand what the different colors on the 2D Sonar screen represent.

The Yellow and Red areas on the 2D Sonar image above represent high reflectivity targets such as fish and hard bottom, while the Blue represents low reflectivity targets such as plants. The strongest return is shown in yellow, while blue indicates the weakest signal. The color pallet can be customized in your fish finder according to your preferences.

In the first screenshot, surface clutter is shown in yellow. At the bottom of the image, you can see yellow and red, representing the water’s hard and soft bottoms.

When looking at the sonar image, you will want to pay attention to the thickness of the line at the bottom of the screen. This indicates how hard the bottom is. A thick yellow bar (indicating our strongest return) will suggest that the bottom of the water is rocky and not soft like sand or silt. However, keep in mind that the thickness can also be affected by the sensitivity of the sonar. At 100% sensitivity setting, bottom may appear very thick, while at 10% it might be very thin.

Identifying Fish

fish under sonar beam illustration

A fish on your sonar screen will look like an arch or a straight line like a worm.

A fish arch will form as the transducer moves over the fish or as the fish moves through the sonar beam. The arch will form if the fish enters the beam on one side and exits through the opposite side, going through the middle of the cone. Arches are usually visible when the boat moves at roughly 4 – 6 miles per hour.

Otherwise, if the boat is stationary and the fish is still, straight squiggly lines like worms are formed on the sonar screen.

Sonar with fish arches

Let’s analyze the above Sonar image. Some of these arches have yellow, which is generally a good sign. It usually means that the fish are bigger with stronger returns. If you see a lot of arches with yellow, that’s a good sign.

However, you can also see some of these returns only have the orangish-red or blue. This could mean that the fish are smaller or near the edge of the cone of your transducer and are returning a weaker signal.

How to Read Down Imaging

Down imaging sonar is a great tool for finding fish, especially when fishing offshore around rocky areas or ledges. With down imaging, you get a much clearer picture of what is below your boat, making it easier to distinguish between fish, rocks, and other structures.

tree branch visible in down imaging

Down imaging returns are typically displayed vertically, similar to 2D sonar readings. The most recent information appears on the right side of the screen.

To best read down imaging data, remember that the sonar return’s strength determines the image’s shade. Softer objects or bottom terrain produce weaker returns and dark shades. Harder bottom terrain or objects generate stronger returns and light shades.

down imaging fish cluster

Down Imaging Sonar is an impressive technology that can show you individual fish. Fish schools will appear on the screen as a tight cluster, while individual fish will appear as solid marks. You can zoom the image on the screen to look at the fish details more clearly.

You can distinguish between bait, game fish, and even different species. This allows you to target only the fish you’re after.

chirp sonar down imaging side by side school of fish
sonar and down imaging comparison

The images above are excellent examples of how the school of fish looks like on CHIRP Sonar and Down Imaging Sonar.

Down imaging transducers typically have two frequencies: 800 kHz and 455 kHz. The 800 frequency will give you the clearest picture in less than 50 feet of water, while the 455 frequency is better for deep reservoirs (up to 400 feet). If you’re looking for a hump or rock pile in depths of 75 feet or more, the 455 frequency is ideal.

How to Read Side Imaging

Most anglers find it difficult to read a fish finder, especially when understanding the side imaging feature. However, with a little practice, you can learn how to use this technology to your advantage.

Sonar Down Imaging and Side Imaging Split Screen

Side Imaging sonar is different from traditional 2D sonar. The sonar history moves from top to bottom instead of moving right to left. The most recent areas you’ve passed over are shown at the top of the screen.

Side imaging explained

The boat and transducer are in the center of the screen, and the transducer beam is displayed as the white line running down the screen.

The dark area in the center of the screen is the water column directly under the boat. The colored area on the left and right sides of the screen is the waterbed. It represents everything on the boat’s left and right sides.

Side Imaging Screenshot

The different shades produced by the side imaging sonar can help you reveal what’s below. The brighter the color, the stronger the return from the object below. For example, a softer bottom or deeper water will appear in darker shades, while a hard bottom or shallower water will appear lighter.

schools of stripers MEGA side imaging Humminbird Solix

Shadows are another thing to look for when reading side imaging sonar. Imagine the sonar beam as a flashlight shining on the objects in the water. If an object is large, it will cast a large shadow. Smaller objects will produce smaller shadows. As in the image above, there are large shadows cast by the school of Stripers.

Fish are usually found around structures. After you have identified the structure by examining the shadows and different shades of return, it’s easier to find fish.

side imaging group of fish
side imaging group of fish 2

The images above show how side imaging can be used to find fish in deep water. The red arrows point to the group of fish that appear as marks, and their corresponding shadows are visible at the bottom of the waterbed. The distance between the mark and shadow can indicate how deep the fish is and where we should place the bait.

side imaging fish highlighted

Another thing to look for when reading side imaging sonar is bait balls. These are schools of baitfish that larger predators are chasing. The baitfish will appear as a tight cluster on the screen, and the predators will be nearby, as seen in the image above.

How to Identify Bait Fish

schools of bait fish on Sonar

In the image above, there are three clouds of Bait Fish on the sonar screen. They are bright yellow along with different colors on the palette. It’s bright yellow in the center which means it is a very dense school of bait, and it’s probably tiny bait.

Tiny baitfish can get very close to each other and form a dense school, especially when threatened by predators. Hence, on 2D Sonar, the dense school of Baits looks like a cloud or lump with the strongest return.

This school of bait fish can be confused with rock or tree if it is close to the bottom. A great way to distinguish that is if you notice that the top edge is smooth, it is likely that you are seeing a school of baitfish. If, however, the top edge is rough, it could be a tree or a bush.

How to Identify Bass

Individual fish usually appear as dots or marks in down imaging and side imaging. Bass swims loosely together and not in tight schools like bait balls.

Bass fish identification

When determining whether a dot is a bass or another fish species, it is important to look at the space between the dots. If there is a lot of space between the dots, they are most likely bass. However, if the dots are tightly grouped, then it is likely another species of fish.

Bass highlighted in down imaging

The distribution of dots on the screen is another indicator of whether a fish is a Bass. If the dots are more spread out horizontally than vertically, you are likely looking at bass. Bass usually stay close to the bottom or suspend in the water column much more horizontally than vertically, so they will look longer than tall on the screen.