Do fish see may fly wings?

Discussion in 'Fly Fishing Entomology' started by Golden Trout, Aug 26, 2012.

  1. Been tying for many years and have tried any number of materials for may fly wings. Just want to hear your opinions on whether or not the wings are actually seen or perhaps represent an actual triggering mechanism in trout.
  2. Hi Golden Trout-
    The short answer yes.

    To understand why and when, read this article.
  3. Really good read in that link
  4. Thanks, Taxon, good stuff.
  5. This will change things. Thanks!
  6. Hi Thom-

    Perhaps so, but I'm really now sure what you mean by that.
  7. Regarding the link you posted. In understanding how a fish sees the fly changes how I will both tie and fish.


    I've been using wings primarily as a camouflaged visual aide to help me locate the fly. That will change.

    I will be trying rubber legs on more patterns and will try to get at least some of the legs of any fly "under the mirror."

    Try to locate the spot where that rising fish was prior to the strike based on what I now know.

    I'll have more confidence in tiny flies now that I know their height also factors in to their ability to be seen by fish.
  8. Hi Thom-

    Thanks for the clarification.
  9. Several comments and corrections on How Does a Trout Catch a Fly?.

    1. The diameter of the window is about equal to the depth of the fish.

    2. The fish is deeper and closer than it appears.

    3. Why are fly rods made to balance with a cast of 30 feet of fly line? The reason is the optical characteristics of the window.

    The window is NOT perfectly optically clear. The 10 degrees along each edge is compressed so that the fish cannot see this area clearly. At 30 feet from the edge of the window, the 10 degree line is at a height of 5 feet anything BELOW 5 feet is distorted and the fish will not likely notice it. So if we stay below the 5 degree line and keep the fly rod below the 10 degree line we can cast to the fish and not be noticed. ( The average angler can kneel him/her self below 5 feet by kneeling)

    The size of the window also compresses the image of the outside world into a very limited space that gets increasingly smaller as the fish gets closer to the surface. You can now understand why, when the trout is feeding selectively and holding just under the surface, we can get very very close to the fish. His image of us is limited by the window size as well as the 10° line.

    Since the edge of the window is closer to you than the fish, just add the depth of the fish to the 30 feet and the added length of the leader to the 30 feet of fly line will still allow you to cast beyond the window so the so the fly and leader will not land in the window.

    What if you are closer or further than 30 feet? I use the rule of 6. The rule of 3 determines tippet size to fly size by dividing the hook size by 3 to get tippet size. Similarly, divide your distance from the outer edge of the trout's window by 6 to find how far above the water you can be before being seen. If you are 18 feet way, you need to be lower than 3 feet, at 24 ft, you need to be lower than 4 feet and so on. Simple

    This illustration is from Gary Borger's book Presentation:


    4. Objects in the window are DISTORTED! 180 degrees of vision are crammed into a 97.5 degree window. That is why the trout cannot see the lowest 10 degrees. Because of refraction or the bending of light by the water surface, only objects that are directly overhead can be seen accurately. As the illustration in Borger's book shows when the mayfly is at the windows edge, it's image is bent so it is elevated ABOVE the surface. Similarly, this bending of light is what causes us to think the fish is further away and more shallow than it truly is (see rule 2).

    The fish has adapted to this distorted view of the outside world but it is not an accurate view. Similarly, we must adapt and place the fish in the correct position relative to us.

    5. The trout can use the mirror to see both up and down. Even when it is looking up it can see objects that would normally be below it's field of vision. So trout can see the river bottom by looking up. Not only can they see things below their plane of vision, they can even see prey hidden behind structure.

    This illustration is from Gary Borger's book Presentation:


    6. There is no need to use rubber legs to get them "under" the mirror. The author mistakenly uses the term under to mean beneath. He has misled you as I explain below.

    In addition to things that break through the mirror and wings that appear in the mirror, there is a third way that trout can detect food. Anything floating on the water, bends the water surface and this causes the angle of light refraction to change. What happens is that small windows are created on that bend surface, and these windows are seen a sparkles of light in the mirror. The feet of a floating insects are seen as depressions and sparkles in the mirror before the wings of the object appear in the window. The author is incorrect in saying that the legs have to break through the meniscus to be seen.

    He quotes Goddard and Clarke Correctly as writing, "It is these star-bursts of light created by the indentations of the feet of the dun floating on the surface, that are the first trigger to the trout's predatory mechanism."

    The author is also incorrect in saying that the body of the mayfly has to break through to be seen. The depression in the surface tilts the surface so that it creates a window through which the body is seen. It body is not sunken below the surface, the surface is tilted!

    In fact, not only the body and legs can be seen. A leader floating on surface tension, displaces the water surface just like a person lying on a trampoline displaces the surface. Since the water surface under the leader is now tilted and not horizontal, this creates mini windows that the fish can see just like the legs of an insect dimple the water surface allowing the trout to detect them even though they are theoretically outside of the "window". Since the light pattern is disrupted, it can be seen by the fish that are looking up AND by the fish that are looking down, because the disrupted light pattern is displayed on the stream bottom as well.

    Goddard and Clarke write, "star-bursts of light created by the indentations". These same star-bursts of light are created by floating tippet and they can be seen on the water surface and on the stream bottom.

    This is important in still waters and the clear slow waters of spring creek type fishing situations where the water surface is smooth. It also only important IF the fish are wary enough that this change in light pattern (either by the floating leader or by leader sheen) puts the fish off. This is one reason why riffles are great places to fish. The riffles create a complex surface pattern that obscures the leader and tippet.

    In England where still water fishing is an art, they treat the tippets so they will sink and not create this "rope of light" attached to the fly. These are called degreasers.

    For more information, there is a discussion and video below:

    Degreasing Your Leader - August 2010 TPO Tip of the Month

    Degreasing Your Leader ? August 2010 TPO Tip of the Month | The Dark Side Productions

    Suggestions for best line degreaser? - Fly Fishing Forums

    How do you degrease leaders? - Fly Fishing Forums
    Patrick Gould likes this.
  10. 7. There are three major differences between human vision and trout vision. They are visual acuity, depth of field, and color vision. I will discuss the first two.

    As computer users, we are familiar with pixel count. The higher the pixel density, the clearer the image. For trout and human vision, rods and cones are the equivalence of pixels. The higher the density of these visual elements, the clearer the image. Humans have a macula, which is an area of high resolution vision and dense concentration of cones. Trout do not.

    A trout has the rods and cones relatively evenly distributed over it's retina. As noted above, humans have a concentration of receptors in the fovea at the center of the macula of the retina so we can see great detail when focused on an object. A trout sees everything at the same detail and it cannot see an object better by centering its vision on it.

    We see 14 times better than a trout because we have 14 times the density of rods and cones in our retina. By comparison, an eagle or hawk has 12 times the visual acuity of a human. So our vision is relatively better than a trout than an eagle's vision compared to us.

    Check out Salmonid Vision at sexyloops.

    A trout has a round lens when compared with a human lens which is more disk shaped. Because the lens of a trout must focus light that enters the lens from water, it needs to be more spherical than a human lens which bends light entering from air. This allows the trout eye have a wide depth of field - IE, the shape of the lens does not need to change much to focus for a specific distance. So to a trout virtually everything is in focus. Humans can focus on a specific object and this allows humans to more easily concentrate their vision on a specific object.


    The seminal article on trout vision was published by an American ophthalmologist, Gordon Byrnes, MD. It was titled, How Trout See: volume 21, issue 5, of Fly Fisherman Magazine, July 1990. pp 56. That article is the work upon which the Sexyloops site and other articles on fish vision have been based.

    This is how we see a standard dry fly. We can see some of the separate "wing" through flat clear water and overlapping hackle.


    Now comes a series of photos showing what the trout sees at increasingly closer distances. The trout sees best at three inches and not any closer.

    Here is a trout's view at one foot.


    At 6 inches


    At three inches. This is as good as it gets for a trout.


    Now here is what a real insect looks like to a trout. Compare it to the fly.

    Mayfly at 6 inches


    Mayfly at 3 inches


    The key question is does that fly look like the mayfly?

    Thank goodness for the poor vision or we would rarely fool it. I think this is why sparkle of flash on a fly attracts or directs the attention of the fish. Although the flash or reflection of a floating leader can attract attention, the flash from an 8X is less than from a 5X. It is all relative to the underlying ability of the trout to see clearly.

    8. The relatively poor vision of the trout brings me to my final point, drag. I think the author is wrong when he writes that drag is noticed because the fish cannot keep the fly at the edge of it's window.

    He notes correctly earlier in the article that the trout uses the windows edge as we would use a gunsight - to lead the fly into it's mouth. If the trout has a hard time keeping a dragging fly at the windows edge, how does a trout ever eat a skating fly or a skittering caddis? It is pretty obvious to me that it has no problem keeping those objects at the edge of its window and a skittering caddis moves much more erratically than a dragging fly.

    The fish notices macro drag early on even with it's poor vision, but because of its poor visual acuity, it cannot notice micro drag until it gets close enough to the fly to notice it.

    So the illustration of Goddard and Clark are a bit misleading in showing us insects in the detail that we see. The article I noted above by Gordon Byrnes, MD is actually what the trout sees. To really understand what is going on we need not only to know the physics of the trout's window which the article explains fairly well. We also need to understand the biology of trout vision and how it differs from human vision. For more complete understanding we need to know how what the trout sees differs from what we see.

    "Discovery consists of seeing what everybody has seen and thinking what nobody has thought"..........Szent-Gyorgy
    Patrick Gould likes this.
  11. Hi Silver-

    Good info, thanks for providing. ;)
  12. Thanks for the kind words.

    As an added note, the poor vision of the trout explains why the size and shape of a fly are so important. With poor vision size is detectable and as the fly becomes closer, shape is detected. Micro drag cannot be detected until the fish gets very close.

    Poor vision also explains what some anglers call "missed strikes". They are actually late refusals. A rising fish has no brakes to stop its rise. So if it sees micro drag just before it is about to eat the fly, it closes its mouth and momentum causes it to bump the fly. The angler strikes and there is no fish hooked because the fish has not taken the fly.
  13. Thanks for the lesson and sorry for hijacking this thread, but...

    A question, does white frothy water modify this at all? I've read it reduces reflections of the surface giving fish a better view of what's on top. Does it reduce the mirror effect or modify the window? Prior to reading the article and your post I thought it simply changed the background color, sort of like how I use different colors of paper for a background behind my vise to provide contrast to the colors of the materials I'm using. I'm now thinking it may do something else but exactly what I don't know.
  14. Hi Tom-

    I don't know; perhaps silvercreek will.
  15. What do you mean by frothy white water?

    1. Discolored water such as chalky water from a glacial run off stream?

    This decreases the distance a fish can see. It is similar to us looking through a fog, except they are looking with poorer vision. It decreases the ability of fish to see a floating fly, and even in a hatch there will be less surface feeding.

    2. Fast choppy water like riffles? There are several factors at work here.

    The water is faster so the fish have less time to decide to eat or not eat. So they make more mistakes and they will take our flies relatively more often that if the water was glassy and the flow consistent and slower.

    Fly Choice - We need to use bushier flies or flies with foam, to get the flies to float so our fly choice is affected by the water type. The flies that are needed to fool fish in very slow flows may get drowned in very fast water.

    The fish see less detail because there is not a consistent window through which to see the fly. The water surface is tilted and the degree of tilt is consistently changing. Instead of a flat mirror ceiling with a clear window the fish sees a disorganized ceiling of mixed and changing mirrors and windows.

    This means we can get closer to the fish because it never gets a good look at us even if we are above the 10 degree line. The roar of the fast water also obscures the ability of the fish to detect us through its lateral line that detects lower level vibrations and noise.

    That is one reason the area behind a rock, in front of a rock, or next to the bank are good places to fish. These are areas that hydraulic forces create a smooth water surface for the fish to see through and shelters the fish from the current. If we do cast consistently into this slow area of water like the "**Secret River" next to the bank, we may need to use a more realistic pattern to fool the fish than if we were to fish the fast riffles on top.

    3. Water with floating bubbles?

    If an area is filled with bubbles, it decreases the ability of the fish to see through the bubbles. I've never seen a river whose surface is covered withy bubbles.

    I like bubbles because they reveal the speed and direction of current flow. The adage of fish the "scum line" is a good one. Bubbles reveal current seam lines and current seam lines are the conveyor belts that bring floating food to the fish.

    Use the bubbles to show you not only where food accumulates, but also to let you know if you are getting drag. Your fly should move exactly at the same speed and direction as the bubble next to it. Bubble are good because they are food and drag detectors.

    **Secret River refers to what Gary Borger calls that ribbon of quiet water along the bank.

    Gary is a friend and I fished the Madison for several days this summer with Gary and Gene.

    The Three Amigos - Myself, Gary and Gene:


    Here are three posts he wrote on his blog about out time together. The first refers to the secret river.

    You might enjoy these photos of Gary as he hooks the runaway trout and his backside as he is chasing it downstream. Believe it or not the fish took Gary well below the log home seen at the right edge of the second photo. We estimated that we were 700 yards or over 1/3 of a mile from where Gary hooked up.


  16. Silvercreek, thank you. You did answer my question. By "white frothy water" I meant something like the water in the right center section of your 2nd picture. My favorite river is a small one with many pools and many of these pools have boulders where the water enters that creates something of a chute. The river also changes elevation quite a bit so the water past these chutes is very well aerated but not all that choppy. These are my favorite spots to fish and now I have a better understanding of why.

    Thanks again for sharing your knowledge.
  17. Great info Silver! I'm a "what is the reasoning behind the action" type of person so I love learning stuff like this.

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