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> > UV Tying Materials - does this really make sense ?, Page 2

PaulRobertsMay 16th, 2014, 7:59 pm

Posts: 1776
I recently read something on UV in mature trout eyes and apparently UV ability is present in fry, then lost. It is then regained at "maturity". Some speculation was that its role may be for navigation coupled with polarized light use. When I heard "maturation" I remembered research I'd read pertaining to the gain of red visual pigments at "maturation" in anadromuous salmon and steelhead, for use in shallow water and nuptial behavior. (I was interested in this research bc it explained the short wave length nuptial coloring in steelhead and all other salmonids.

Made me wonder if the reference to UV sensitivity in “mature” rainbow trout has a purpose other than feeding, and whether it is an annual event with “annual maturation” –associated with nuptial coloring, kype development, and nuptial behaviors. Would resident rainbow populations maintain this year round?

Mack's question of whether UV vision is useful is a valid question not just for fisherman but for fish too. Evolution tends to prune less than useful functions due of energy allocation pressures.

Interestingly, female largemouth bass have been described by some anglers as “lighting up” –taking on a very UV lavender “aura”. Doug Hannon talked about this in his writing. And I’ve actually seen this too, but so infrequently (despite looking at spawning bass closer than most) that I could say it’s always present. Maybe in situ lighting was involved?

Also, I’ve always noticed that post-spawn brown trout, in particular females as they recuperate (and a get “metallic” sheen again), have lots of bright UV-ish looking blue pigment on their bodies, especially on the gill plates and forward parts of the sides of the body.

And, come to think of it… is the very pretty pale blue pigment in resident stream brown trout –usually there’s a spot behind the eye (often associated with a black spot), and the blue halo’s around the black spots on the sides (esp fore)– UV reflective? If so, this would suggest social visual cues in the UV range amongst trout. Is this maintained year round? Is it more prominent in clear water, turbid water, shade, sun?

This one is lacking the black spot behind the eye, or maybe it's obscured. Anyway, it shows a lot of the blue pigment:

Anyway, all purely speculative. The simplest speculation is that UV vision and red vision in resident trout is permanent and applicable for visual cues and for feeding. Since UV reflectance is common in the terrestrial insect world it would make sense that rout might retain UV sensitivity. But I doubt seasonal changes in trout vision has been pursued very far.
OvermywaderJune 20th, 2014, 6:40 pm
Posts: 31Paul,

I put together a short paper on the issue of ultraviolet vision in trout. It may be found at I would appreciate your criticism, perhaps finding holes in my logic.

EntomanJune 21st, 2014, 8:41 am
Northern CA & ID

Posts: 2604
Very nice article, Reed. Well articulated and certainly reasonable. Perhaps you are right.

However, it seems to me the bigger question is what to do about it. As I've asked before, how do we address it? Your photos filtered for UV show a much different picture (pardon the pun) than what the fish see, assuming they "see" UV. For example, lets further assume we can't see green. If we filter for the entire band we would associate with green and then converted it to a visible color - say red - we'd be off the mark in terms of what the trout actually see. Your photos, while interesting, present this very problem. Similarly, to simply tie with a broad spectrum reflecting uv material may be like fishing with a Kelly green fly to match the dusky olive of so many of our hatches. How do we detect the subtle shading and blending with other colors that can often be important?
"It's not that I find fishing so important, it's just that I find all other endeavors of Man equally unimportant... And not nearly as much fun!" Robert Traver, Anatomy of a Fisherman
OvermywaderJune 22nd, 2014, 5:29 pm
Posts: 31I think I understand your question. Let us say that there is a dusky olive fly hatching. I would choose a fly with colors of body, wings, and tail that were nearest to the colors of the original. That is what we do now. However, if it is a mayfly, I would know that the wings would have some bright marks in the UV, so I would add some transparent, in visible light, highly UV reflective spots on the wings of the artificial. If it was a caddis I was imitating, I would use a low UV-reflective - say 25% - coating to the wings. That way, if the underlying feather wing was highly UV-reflective, I would overcome that with my topical application. So, I don't need to know what the artificial looks like in UV, so long as I know some common attributes of the insects and other trout food and have a means of adding appropriate UV highlights.

EntomanJune 22nd, 2014, 9:48 pm
Northern CA & ID

Posts: 2604
Yeah, that's what I was getting at. Very good info, Reed. Makes sense... Thanks for sharing it!
"It's not that I find fishing so important, it's just that I find all other endeavors of Man equally unimportant... And not nearly as much fun!" Robert Traver, Anatomy of a Fisherman
CaptainconJanuary 5th, 2015, 2:10 pm
Posts: 2
Am coming late to the parade, but noticed one thing missing from all these order for UV to be effected, a UV lighting source is required. Things fluoresce under UVA, UVB or UVC, LW/MW/SW, respectively, dependent on the wavelength. UVC and UVB are basically absorbed by our atmosphere so unless you are underwater with a UVA lamp lighting your fly, the sun will be your only fluorescent illumination source. And since sunlight is dispersed through water up to 60% at only a couple of meters, UV illumination (fluorescence to us) will be nominal...and zero w/o sunlight.The thread that presented UV viability in young trout is probably most correct since it is the plankton that respond to the UV photon that allows young trout to better see their food source...quit eating plankton and UV ability disburses...and for the record, there is no UVR (reflective) that is referenced in the fly tying marketing material. UV light is either observable or not, the UV light is not "reflecting" off anything, the same way white light does not reflect off the page of the book you are reading.
TroutnutJanuary 5th, 2015, 5:05 pm
Bellevue, WA

Posts: 2555
UV light is either observable or not, the UV light is not "reflecting" off anything, the same way white light does not reflect off the page of the book you are reading.

That doesn't sound right to me. Can you clarify what you mean?
Jason Neuswanger, Ph.D.
Troutnut and salmonid ecologist
OvermywaderJanuary 9th, 2015, 2:45 pm
Posts: 31CaptainCon,

I am confused by your statements as well. Most of those things we see in the world are visible because of diffuse or specular reflection (computer screens are one exception, because they emit light in various wavelengths). When I look at a book, the page is white to me because the paper is absorbing little light and reflecting a nearly equal amount of red, green, and blue wavelengths (and UV and some IR). A red object is seen as red, because all the visible wavelengths below 620nm are absorbed, but the wavelengths between 620 and 700nm are reflected.

Solar ultraviolet light has been measured in viable amounts at a depth of 600 meters in sea water. SCUBA divers use fluorescent patches on their wetsuits and fins because UV will cause the patches to fluoresce at great depths.

We have been using UV reflective materials in our flies since the first fly was tied, centuries ago. All materials reflect some amount of UV. And mature trout can see the UV reflectance. See for more info.


CrepuscularJanuary 10th, 2015, 9:46 am
Boiling Springs, PA

Posts: 919
UV light is either observable or not, the UV light is not "reflecting" off anything, the same way white light does not reflect off the page of the book you are reading.

Huh? I too do not understand this? I'm no physicist by any stretch of the the imagination, but I'm pretty sure that the only colors we see are those wavelengths of the visible spectrum that are reflected off an object. I think some guy named Newton figured that out.
WiflyfisherJanuary 13th, 2015, 10:19 am

Posts: 612

My new killer pattern. :-)
John S.
CaptainconJanuary 13th, 2015, 11:54 am
Posts: 2
Apologize for the apples and oranges comment...was focused on fluorescence and not the visible perception of invisible (to us) was an incorrect tangent.

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