1. Troutnut Forum
›
2. Fly Fishing
›
3. UV spectrum and trout

Most of us have had a trout hit a fluorescent strike indicator, and after seeing some photos on the web of scorpions under black lights, I've begun to wonder about insects that trout eat and uv dubbing. Do trout foods react with uv light, and do trout see and respond? If so, might dubbing that includes some or all uv reactive materials provide another trigger? Are there any studies on this?

I picked up an interesting book on this subject recently, "The New Scientific Angling: Trout and Ultraviolet Vision" by Reed F. Curry. Unfortunately I haven't had time to read it, so I can't summarize. I can, however, give basic answers to your questions. Many aquatic insects do reflect UV light, and the trout can see it.

I don't know if there are experiments showing whether they respond to it or not, but I think it's probably like any other stimulus (including other colors) they could potentially key on when forming a search image for prey.

Interesting Jason, I didn't know bugs reflected UV. My only understanding about UV was to try and avoid it with clothing as it makes you stand out from trees, rocks, etc. I know bugs are attracted to black lights...

I've always wondered what it looks like to animals like deer. The visible spectrum (to us) has gradations of difference, so why not UV? I also wonder why deer need to see it, but we don't.

“Understanding Trout Behavior” by John Goddard & Brian Clarke.

Although they do not address UV light they do cite scientific studies on how trout have been shown to react to our visible spectrum. They claim studies have shown that the color red is most easily seen by the trout which is, if I’m not mistaken, at the longer end of the light spectrum.

Great book, Alan. Very thought provoking. I've often wondered about those studies. It's interesting that trout apparently see best that color that most quickly fades the deeper it gets or the less ambient light there is. The chapter that talked about line color really impacted my outlook on the subject.

When they first started making synthetic dubbing in the 1970's someone sold a box of 24 plastic pill jars each with a different color. One of them was a dark maroon/purple. I tied a hares ear with that and had such good luck with it that for years my friends and I used nothing else when we fished nymphs. Even bought several more vials of just that color. Since I often was standing around a blacklight with my fishing jacket on it wasn't long til I noticed that the purple hares ear fluoresced. Always wondered if that is why the trout loved the thing.

I found the discussion of the "prismatic ring known as Snell's Circle" rather interesting. I have not seen that mentioned elsewhere.

I did a little quick refresher research and was reminded that fluorescence and reflecting UV are two different things. The former ability is due to the presence of phosphors that absorb UV and emit the energy back as light in the visible spectrum (such as your purple dubbing, Dave). The latter capability actually reflects UV much like an apple reflects light in the red spectrum. Such critters capable of this would look black to us (or at least those parts that do), even if held under a black light.

As an aside, it is ironical that outdoor clothing companies go out of their way to stop their clothes from fluorescing in response to demand created by "hunting experts" that really has nothing to do with game's ability to see UV. In any light other than pure UV (black light) these fluorescing qualities are muted by the reflection of normal light off the material to barely be noticeable unless it contained a super abundance of phosphors (fluorescent material). Those ads you see in outdoor mags of fluorescing hunting clothes glowing bright in a field of gray are not the way game sees the stuff, any more than we do. Another irony is that since game animals are supposedly poor at seeing reds and oranges, low light fluorescence in these colors are probably not picked up by them but seen very well by humans. The ability to see red and orange well comes in handy for an animal destined to master fire. Also comes in handy for not mistaking others of their kind (if they are wearing these colors) when using fire to launch deadly projectiles.:)

Anyway, back on point - the real question is since everything that looks black to us doesn't necessarily look black to the trout, what does it look like? More importantly, how do we imitate it?

Allan -

You're right, it's in Chapter 7 on what the trout sees of our flies and I've never seen it mentioned in another angler work either (that I remember). It is the best case for the importance of both wing and body color even with a bright sun overhead (and the reason why I don't throw in with those boys that think wing color is not all that important). One would think all a fish sees is a black silhouette with the sun behind the bug, but tain't so. I must admit to often forgetting this lesson.

For you guys that don't know what we are talking about, Snell's circle is the thin rim of the window where it meets the mirror. It acts like a prism that allows the fish to see the full colors of the critter without the back lighting that occurs in the rest of the window. This explains why the sophisticated buggers will usually drift holding the fly in this zone while inspecting it, especially when the sun is high overhead or in their faces.

Chapter 8 on what the trout sees of us and our gear is worth reading over and over. Heck, the whole book is! I generally keep it locked away with Datus Proper and only bring them out to conjure up new tactics for tough fish I encounter and plan on visiting again.;)

BTW - No more talk about this book (other than PM's)....The more obscure it is the better, AL. It's out of print and unobtainable, isn't it?:)

I can remember my "glow bug" days where my little corkies were painted with phosphorescent paint I believe is the term. We'd "energize" our glow bugs with a flashlight, and some used a camera flash to energize them. They'd retain their light bulb effect for a few casts. Got to be mesmerizing watching that glow bug bounce down the stream. When the glow bug disappeared you'd set the hook, and mine did behind a rock, and I set my graphite rod hard under a low level bridge, that I'd forgotten I was under. That was the end of my steelheading at nite.

That set me straight and to thinking. I always assumed (there's that word again), that a trout looking up at my fly was seeing a silhouette. What about my nymphs? I guess they are seeing true colors, too?
Bruce

Back when I was at University a researcher in fish vision had a lab down the hall from mine. He was at the time doing some research on UV vision in fish. I queried him on it and his work was preliminary at the time but from what I remember and what I was able to read, that UV sensitivity is mostly in fish at the fry stage. It was believed they employed it to better resolve zooplankton in very shallow waters. Apparently, UV does not penetrate far into water, and then only in very clear water. Also, not all species looked at possess UV sensitivity. If I remember right trout fry possess it as do bluegills and yellow perch, the latter possibly into adulthood. I thought that trout lost that sensitivity by adulthood.

I believe there has been more research since but I don't know where that stands. Jason, will you do a book report? :)


We used to fish phosphorescent casting spoons before daylight for trout on Lake Ontario. They worked remarkably better than standard finishes in pre-dawn light. We did not energize them much with lights as that wasn't necessary. Too much light was not good I remember. We threw painted fluorescent colors on dark overcast days and shiny metallic reflectives on bright days. Appropriate visibility was key.

To this day I also put phosphorescent vinyl fabric paint dots on my rods as a measuring tape. They show up well in low light and in full darkness a camera flash supercharges them. Just turn your head away when you do it.

Thanks, Kurt for making the distinction between fluorescing and reflecting uv; it is the former that I was thinking of. For example, put your apple caddis pupae under a black light and see how they look. Like Creno, I've noticed that some favorite dubbings fluoresce under black light, and linking that fact with the photos of scorpions under black lights I've wondered the same thing that he did: is this quality a trigger? I guess the thing to do is get some mayflies, caddis, etc. under a black light to see how they look. And, I suppose that even if they don't fluoresce, it still may be a trigger for some other reason. Curiosity even. Trout are, as we know, strange critters.

Most shallow water fishes see red since it is only available there. It's believed it originally developed as a counter --a contrasting receptor-- to background colors that prey fishes developed camouflage in. That's the evolutionary understanding. It's bolstered by some interesting research. Apparently salmon and steelhead are esp sensitive to blue-greens, the background (most light available) in an open ocean photic environment. But being anadromous, when they come shallow to spawn, they develop a red sensitive pigment that helps them in shallow water. It also is the important nuptial color. I believe something similar may happen in all salmonids as they each use reds in body pigments in shallow waters. Late summer and autumn browns seem to become particularly "ornery" around reds (my explanation for why that feisty male brown in one of my trip reports a while back, struck an apple floating downstream!

Largemouth bass have two pigments -a green and a red. It is believed the green is sensitive to algae-tinted and vegetated background color (most available reflected light) and the red (the complement of green) is a contrast color that helps bass pick out prey against the green backdrop.

I remember hearing a lecture given by Bill McFarland on this very phenomenon, the evolutionary development of fish visual pigments. It was a stunning presentation in which he used color filters and fish cutout images to show how the systems worked. Very, very cool I thought.

Maybe Jason will have more to say, or correct me in my rudimentary understanding.

Yes to both, Bruce. What is also true is that we aren't quite sure what that means in terms of fooling trout. The fact is trout often respond in ways we can't explain. Why do trout often prefer orange or purple when they're chomping on olive baetids? I've had times during PMD hatches when perfectly matching sulfur is rejected time after time while the same fly in tannish gray slays them. Your recent topic on Baetis nymph color is another case in point. Excluding my Ripe Nymph (that's really fished as an emerger of sorts) and the BH American PT (with a flashabou wingcase that I fish as a general attractor), I use only three nymphs in baetid shape to fish deeper in the column pre-hatch: A black AP (often tied with a flashabou wingcase), a paler olive nymph based on the Oliver Edwards design, and the venerable PT Nymph (original Sawyer version). The latter is by far my favorite, especially if the nymph is to be moved at all. Yet, I've never seen a baetid nymph that color. Still, all things being equal, I admit to trying to design flies that match the form and color of the naturals as closely as possible - but I also try to do this without crossing the line into the "dead zone." I'm firmly convinced trout don't like sculptures as a general rule. Way ahead of size, form, and color is life. I've found If we don't simulate that effectively, we're usually wasting our time. There's something special about hair and feathers in their various forms...:)

High Summer & the color red... Interesting, Paul. When I was a boy, trout fishing meant the High Sierra's for my family. This was way before tail waters, the ascendancy of "matching the hatch" and the opening up of the Spring Creeks further North (Hat Creek was full of course fish and Fall River was locked up tighter than a drum). Until run-off was through (which in many years meant after the 4th of July) worms ruled. That was Spring fishing to me. Summer fishing (July, August) was for dry flies. Other than the Caddis Bucktails he carried for caddis hatches (the palmered precursor of Al troth's famous fly), my dad was a firm believer in having red on the fly. His favorite patterns were the California Mosquito, Gray Hackle Yellow, Professor, Hair Wing Royal Coachman, and the Rio Grande King - all with red tails... His philosophy in fly selection was crudely based on matching the hatch by selecting the "proper" fly from his gray, yellow and green box. He carried mostly 12's but had an ample selection of 14's and 16's as well. If those didn't work, out would come either of his two attractors. There were no fly shops and you couldn't buy a decent fly anywhere except from Abercrombie & Fitch in SF, so by necessity we were fly tiers. I give him credit for not putting gold tinsel on the GHY or the Professor as was proscribed for those patterns. He said it made the flies too heavy (this was before mylar) and unnaturally bright so he ribbed them with white thread. But they absolutely had to have red tails! Catching all the fish we wanted was never a problem and we seldom saw other fly fishers.

This had been his mind since the late 40's. The only change to this canon I remember was the discovery of the Adams at some point in the mid to late 60's, probably from an article by Joe Brooks in Outdoor Life (this was before Fly Fisherman magazine). I remember we had a heck of a time learning how to dub properly so we just used gray wool yarn for the bodies. I have no idea where he got us our hackles. Later as the 60's ended, he became much more "sophisticated." I don't remember the turning point other than it was around the time we made our first forays into the Fall River country and Swisher & Richards came out. Anyway, we abandoned his precept regarding red tails and simplified fly selection. I wonder...

My how things have changed. The 1960s was a turning point, into exponential change in knowledge.

As to the color red ... Red tails on flies may have had as much to do with our own fixation on red than anything else. And it persists to this day: Red hooks, "bleeding bait" finishes, and red fishing lines are clear evidence of our mis-directed predilection for red.

Here's a poem I wrote on a bass fishing site about the subject, bc it was annoying me so much. The poem later turned up on a couple poetry sites (Fancy that!).

Seeing Red...a poem...Ahem...

Red is an apple ripe on the vine
Red is of stemware, grapes and wine
Red is of tumescence, lipstick, lingerie, and high high heels
Red's pretty important to people
Tackle manufacturer's see Green when they offer Red
Makes me see Red!

I remember an article in a Frank Amato WestCoast Mag. written by a Japanese Scientist on the visibility factor. Red dissipated rapidly as the depth increased, but he had a picture of a diver at some depth in salt water I believe. The diver had a number of different colors on his suit, but the one that was displayed very visibly was a fluorescent, red band around his wrist. Hopefully I am accurate on that account. He was emphasizing the huge difference in visibility between normal red, and fluorescent red.
And I kid you not on this one. The lure that shutdown our sockeye fishing one Summer on Lake WA adjacent to Seattle was the red, bare hook! There was a quota catch placed on the fishery, and once the anglers discovered the bare red hook, the quota was reached very quickly.

I've seen those photos too, Jere. What's going on there is the high frequency UV that does penetrate deep is "charging" the phosphors in that red material, which really stands out against the dark blue water.

Another interesting characteristic of the red wavelength is seen in the evening. You know those diamond sparklies caused by refraction from the insects feet and wings trapped in the meniscus during the day? Well it turns out that in the evening as the sun crosses the horizon, those diamonds turn to rubies. Since the mirror is then dark they stand out like little red beacons to the fish. Photographs of the phenomenon are amazing. Perhaps another reason for the trout seeing (needing to see) red so well?

Paul, why mis-directed? I've seen the idea that a bit of red for gills, or for blood, is a strong trigger so many times that the concept has become imprinted on my brain. Has red been disproven as a trigger for fish? (I still remember the old "tried and true" red and white bomber in my dad's tackle box--caught some nice fish on it, including some trout.) And what about that apple?

This is a long story I guess. Quick synopsis:

Over time I've come to consider color to be one of the least important variables in fishing presentation in general. There are times, places, and reasons where color (or at least visibility, but sometimes hue) can matter. But I believe color is way more important to humans than it is to fish. I have seen MANY examples of this phenomenon over time. This is an inherent (and strong) bias that lure manufacturers take advantage of. The only reason there are 200 different color patterns available in a popular trolling spoon for trout is bc people are attracted to them (makes them go "ooooooo" and buy them) and they'll even afix magic properties to favorite or novel color patterns that have nothing to do with water and fish. People fool themselves very easily. I have lots of anecdotes I could share that show this.

It's not that I don't think that red has been disproven as a trigger, it's that I don't think it's been proven in any rigorous way. Too many variables. Fisherman are NOT reliable sources. I’ve seen WAY to much blind bias amidst the myriad of variables that exist in nature. Red head lures may simply be more interesting to anglers than to fish. And when they do outshine a more drab color, it may have more to do with visibility than "red". Or confidence in the angler.

In my mind, red gills, red spots, "blood", red spots, excite anglers WAY more than fish. Bass evolved catching bluegills and crayfish. I’ve watched many successful kills and have never seen blood. Now shad can be different, but even then, a damaged shad is more apt to be missing scales than bleeding. Now throw some bluefish in there (called “choppers”) and you may have something there.

Again, that's not to say that there are times and places; I'm just talking in general, where people should be concentrating their time (and mysticisms). The apple may be, is likely, one of those times when color mattered. The fact that anadromous salmonids gain a red sensitive pigment upon coming shallow, that reds (and oranges) are important in the visual aspects of nuptial ritual, that aggressive territorial males get the brightest color (females the palest), lead me to be believe that color (reds esp) helps identify rival males. This is true in a fish in which nuptial rituals are very well studied, the stickleback. Males are heavily patterned and exhibit red while females exhibit pale silvery color (lack of color) and individual fish use these patterns for recognition.
http://www.dailytech.com/Canadian+Researchers+Recreate+Climate+ChangeDriven+Fish+Evolution/article19266.htm See the second image.
A pale silver dummy female lowered into the tank can elicit courtship in male sticklebacks, whereas one with a red spot gets attacked. There are many fish well studied in which imm males sneak past a dominant male to spawn by mimicing the color of females -namely having no color. This has been shown for bluegills as well as many freshwater cichlids and saltwater reef species. Many gamefish, including trout and bass, also have more heavily patterned males and paler more silvery females.

So… It was my speculation that that male brown bit that size 5/0 apple bc it was screaming RED! It was early September (early pre-spawn) and that large male (for that stream) was aggressively spanning the length and breadth of the pool chasing other trout it encountered. It wasn’t just displacing competitors from feeding lies, it never held a feeding lie for more than a few moments to rest. It appeared to me that hormones were flowing. When that apple drifted into view I was amused to see it rise right up and take an aggressive bite at it. My guess is, although I‘m curious, it would have done so with an orange, or a chartreuse tennis ball (also common flotsam in this section of urban stream). So I’m not sure if RED is the only game in town, but since all salmonids including almost all browns have some red (at least in spotting) that red is potentially socially significant and a likely target for aggression.