So tell us please, does the fish retina have the same color sensitivity as humans?
Dr. K really goes into this in detail, particularly as it relates to salmonids.
A fish's eye actually has three different types of light receptors (the old rods and cones thing). Looking upwards, the corresponding area of receptors inside the eye is optimized for differentiating dark objects against light backgrounds. Looking downward, the eye is optimized for seeing light objects against dark backgrounds. Only when the fish is looking at something at eye level is the eye optimized for seeing variations in color.
He also notes that when salmon and steelhead first arrive from the ocean, their vision is biased towards blues and greens, and the closer they get to spawning, the more their vision shifts to the red and orange spectrum.
Overall, what has struck me about the Kageyama book is how difficult flies can be to see underwater, particularly when the fly is in deep or murky water conditions or even when the sun is shining brightly. He makes the point, as we all have experienced at one time or another, that in clouded water conditions on a river, you really have to smack the fish in the nose with the fly to get a take. If your drift is off by a foot, sometimes that's enough for the fish not to see the fly in time. It's obvious here that a more visible fly would be more productive than a more hatch matching pattern.
Follow a sample of his reasoning based upon his studies and wide fishing experience: if you are fishing a nymph that the fish would normally see above its eye level (obviously a common occurrence), bright sun, bubbles and froth, and a bright sky all make it difficult for the fish to see your fly. In this case, a black fly is the most visible (highest contrast against the background). A white fly would be backlit, but would tend to blend into the bright background, not contrast with it.
Similarly, something reflective such as wire ribbing or a bead head also helps the fish spot the fly, but a metallic brown or gold is recommended over silver. Why? Dr. K describes it very well. If you are driving in dense, luminous fog, someone driving with their lights on is not very visible to you. However, if that person is driving with amber tinted fog lamps, that coloring contrasts with the prevailing white and is quite visible even though it is also quite light. The metallic brown or gold bead serves the same function.
The immediate influence his findings have upon my flytying are that I will tye favorite patterns in at least two versions: one to fish on overcast days or when the fly is fished deep, when the water is murky or when the prevailing background that the fish will see the fly against is dark. The other version would be for clearer water, bright conditions, shallow fishing and when the prevailing background that the fish will see the fly against is light.
For a particular pattern I might use more silver or white, black and fluorescent colors in the first (dark) case. I would use more copper or brass and black or dark brown in the second (light) case. Flash materials in general work because they help the fish see the fly.
Just altering favorite patterns to account for two prevailing extremes of light conditions would be a major change in my thinking. They would be tools, just like having the hatch-matched, natural material imitation would be a tool.
But just tying patterns in two versions would be a gross oversimplification of Dr. K's conclusions. There is so much more to this, particularly in regards to a very careful selection materials for tying.
But, based upon my fishing experience, Dr. K. really has this one dialed in... It will be fascinating to pursue and test.
A moderate caveat...the book is oriented toward steelhead fishing and lures, although flyfishing is covered. What you will conclude, as I did, is that few flyfishing materials produce flies that are easily visible to fish under more difficult conditions. And difficult conditions can be as simple as having to fish your fly more than five feet deep on a cloudy day!
Wes Wada Bend, Oregon
