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Old 11-11-2012, 02:04 PM
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Default Re: Does blue excite the trout?

Originally Posted by nrp5087 View Post
On Thursday evening at my flyfishing club my professor told me that the color blue has been proven to excite the rainbow trout and other species. This was determined from placing a sensor into the optical lobe of the trout and presenting the color blue to the fish. I decided to test it out and tied a blue wolly bugger with red hackle and this is what i caught out of spring creek PA
I have a contrary view to your professor.

First let me state that I have also heard that rainbow trout are sensitive to blue, hence the Patriot fly which is a version of the Royal Wulff with blue floss substituted for the peacock herl. So I have had time to think about the proposition that blue is a good color because the color stimulates the trout brain.

Click the image to open in full size.

However, I hate it when professors say that kind of stuff. It is way more complicated than the response in an occipital lobe of a trout. I think your professor has overstated what actually occurs. Color vision depends on the cones that are in the retina of the trout. Trout have 4 types of cones to our 3.

Humans have red, green and blue cones:

erythrolabe; peak absorption at 565nm; red
chlorolabe; peak absorption at 535nm; green

cyanolabe; peak absorption at 440nm; blue

Trout have 4 sets of cones

Red 600nm
Green 535nm
Blue 440nm
Ultra Violet 355nm

Note that their green and blue cones are IDENTICAL to our green and blue cones. They see into the infra red with a longer wavelength of 600nm and into the UV centered at 355nm. The UV cones disappear as the fish matures so adult trout have exactly the same green and blue vision that we have. Adult trout do NOT see into the UV and are not sensitive to UV.

How does you professor know that trout are more sensitive to blue than humans? I can understand operating and put a sensor on a fish brain. However, have they done that to a human? I doubt it. If not, then he cannot say that the trout is more or less sensitive to blue than humans are.

In addition, even if the color blue has a greater response in the brain that the color red, there is no proof that this has a linear effect in feeding behavior. We could as easily theorize that the color blue is more vibrant and scares the fish.

I could state that the reason blue has a stronger response is that it is a survival benefit that helps them identify predators and that therefore, the color blue scares trout. Do I have evidence for that? No, but if a professor said that in a lecture would it be believable? Yes.

I have heard many things in lectures that have later been shown to be false. I suggest that this is one that needs further evidence. How can further evidence be provided?

There must be chain of evidence to "prove" a theory AND there must be NO OTHER reason that could explain the result. Both tests must be met. In this case, there is no such chain of evidence PLUS there is an alternative explanation. Here we have only the evidence that blue results in a response in the occipital lobe but WHAT DOES THAT MEAN in terms of behavior?

The reason I say this is that I tied up the Patriot fly and found it to be ineffective on rainbows compared to a regular Royal Wulff. The peacock herl was better in my experience.

Is there other phenomena than can explain why fish might respond to blue when they don't to red? Yes, there is. It is because the color blue has a shorter wavelength than the color red and blue light has higher energy so it penetrates deeper into water. The color blue is also more easily reflected back. That is why the ocean looks blue and not red. Water is colorless but deep water looks blue because blue light penetrates deeper and is more easily reflected back to us. So fish can see blue from further off.

So if fish react to blue and your professor says it is because of the occipital lobe response, he needs to disprove that it is because they can see the color blue from further off and in deeper water.

Why is the ocean blue?


"Discovery consists of seeing what everybody has seen and thinking what nobody has thought"..........Szent-Gyorgy
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