A fishfinder is a special tool that helps people who love to go fishing to find fish in the water.
It looks like a small computer screen that you can put on your boat. The screen shows color pictures of what's happening underneath your boat in the water.
The fishfinder works by using sound waves. It sends out sound waves that bounce off objects in the water, like fish, and then come back to the fishfinder.
The fishfinder then uses those sound waves to make a picture of what's in the water. You can see if there are any fish around and how deep they are.
This helps you know where to go to catch fish and how deep you need to put your fishing line in the water.
It's like having a special map that shows you where all the fish are hiding. And if you're lucky, you might catch a lot of fish and have a great day of fishing!