Fishing Forum

What does our fish finders see? The fish of a part of the fish? I had heard that it bounces off of a part of the fish, but that doesn't seem right to me. Any one know?
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Easy, it sees the block of air in the fish. The less air, the less of a signal return. Ocean salmon only inflate their air bladders when chasing bait up in the water column so they are rarely seen on a fish finder. As soon as they enter fresh water they need the added buoyancy so they can be seen on the finder.
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Thanks for that information
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A sound wave is produced by the fishfinder and sent through the water. At the source, the wave is narrow; however as it penetrates deeper, the sound wave spreads forming a cone, or what is commonly called a beam (think flashlight). When the sound wave encounters something within this beam, it bounces back to the fishfinder. By measuring the very small amount of time between when the sound wave was send out and when it bounces back your fishfinder calculates the distance and draws it on the screen.
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Interesting technology to say the least...I understand its bouncing off the air bladder inside the fish...so fish like Gobies dont have bladders and cannot suspended in open water dont show up on the sonar...It seems Kokanee dont seem to show up much either since I always get hit when nothing is really on the screen...
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[quote Jimbojump]Interesting technology to say the least...I understand its bouncing off the air bladder inside the fish...so fish like Gobies dont have bladders and cannot suspended in open water dont show up on the sonar...It seems Kokanee dont seem to show up much either since I always get hit when nothing is really on the screen...[/quote]

If a fish with a bladder, like a perch, is sitting right on the bottom, you may or may not see it depending on the resolution or "separation" on your sonar. Some will see .5 inches of separation between bottom and a fish or fish to fish while others may require 2 inches (or possibly more) depending on the unit you have.
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Don is so correct about the ocean. We sometimes can see the salmon schools surrounding our boat shortly after landing a fish....15 or 20 coho or pinks.....and not so much as a blip on the Humminbird. But it will pick up a small bottom dweller at 400' or a school of herring or candlefish with great accuracy. Mike
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[quote Jimbojump]Interesting technology to say the least...I understand its bouncing off the air bladder inside the fish...so fish like Gobies dont have bladders and cannot suspended in open water dont show up on the sonar...It seems Kokanee dont seem to show up much either since I always get hit when nothing is really on the screen...[/quote]

Kokanee have the largest air bladder for the size of the fish of any fresh water high altitude fish. They should be seen easier than trout and show up as larger arches than trout. I can usually tell the difference between species simply by the return using a quality aftermarket transducer like the P66 or better on a Lowrance or Furuno unit.
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[quote MMDon]Kokanee have the largest air bladder for the size of the fish of any fresh water high altitude fish. They should be seen easier than trout and show up as larger arches than trout. I can usually tell the difference between species simply by the return using a quality aftermarket transducer like the P66 or better on a Lowrance or Furuno unit.[/quote]
Where do I find this "P66"...who makes it?I just installed a Lowrance elite 5 unit and wouldnt mind something that improved it
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Airmar makes the P66 and other sonar transducers that allow you to even see fish at normal boat speed rather than seeing a black screen. I'll send you a link to where you can get them.
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