My article first appeared in Fly Fish America magazine Feb 2000.
So many fishing lures available today boast about great attractive powers. Some lures rattle, some click, some fly. On balance, these "lures" are designed and built to hook fishermen, not fish. Why should fly fishers care about lures? The more I see fly tiers adding gimmicks to flies, the more their flies resemble lures. The more I see flies resemble lures, the more seriously I appreciate them for strictly flyfisher "entertainment" purposes. Understanding how a fish sees will help you tie flies designed, not to entertain, but to catch fish.
A fish lives in water, which just like air, is a fluid. Being a much denser fluid, water greatly impacts the properties of light. Like our eyes, fish eyes have a cornea, an iris, a lens, and a retina full of rods and cones, but many functions of the fish's eye are modified to deal with the impact of a water environment and produce excellent underwater vision.
Two major lens modifications affect the fish's vision profoundly - its lens is round, and it is much denser than our eye's lens. The fish's lens can therefore focus heavily refracted light on the fish's retina, so it clearly sees objects under water. To vary its focus, the fish moves its lens forward and backward. A freshwater fish is naturally farsighted, so when it wants to focus on close objects, it moves its lens moves back from the cornea and closeup focus is achieved. Fish enjoy a tremendous field of view, with 180 degrees of overlapping vision from both eyes. With their swimming motion and eye movements, fish generally don't have blind spots behind them, and have good depth perception.
Fish don't need or have eyelids for keeping their eyes moist, thus many fishers believe that fish cannot control the amount of light entering their eyes. They believe fish hide in low light areas to escape bright light. WRONG! The fish eye controls light in a different way than our eyes do. Instead of an iris closing, or eyelids closing cutting down light into the eye, according to Dr. Bob Reinert, professor at the University of Georgia, athens, "the fish uses synchronized movement of the rods, cones, and pigment granules in the pigmented portion of the retina" to control light entering the eye. One drawback to the method is that changing from low light to bright light may take a fish much longer than it takes us, but he can handle great variations in light.
Fish can see color! According to Dr. Reinert, "One of the best indicators that at least some fish see color is that they have cones, which are the color receptors in higher vertebrates. Another indicator is that many fishes are highly colored, and the most colorful fishes are found in shallow, well-lighted waters, where they are exposed to the full color spectrum." Based on testing, the primary biological advantage of color vision for a fish is being able to contrast food targets against a variety of backgrounds. As a fly fisher, you should know that color can really impact a fly's effectiveness at times.
What are effective flies? According to Doug Hannon, the "BASS Professor", from the fish's eye view, small flies emulating an abundant source of prey that glide quietly through the water with the least amount of turbulence would be most effective, because that is how real prey behaves underwater. These small, quiet, simple flies, tied in natural colors don't give off negative cues which the fish see and sense. Sized to match available food sources, they can be presented to emulate the actual prey's motions. For example, crayfish may sink slowly, then dart off in short motions, settle to the bottom, and dart off again. Minnows will suspend, change directions, suspend, and slowly swim away. All are small, quiet, food organisms. Small crayfish, minnow, and leech patterns seem natural and are VERY effective for warm and cold water fish. Know the impression and natural actions of the prey you're trying to emulate, then tie your flies with materials that create the impression of the organism and present it naturally. Seen through the eyes of fish, your flies will appear natural and will catch many more fish. Keep the gimmickry out of your fly designs and keep your flies effective!
A tremendous resource on fish biology is entitled FRS 330, Fish and Wildlife Biology, by Dr. Robert Reinert, 1997, available at the University of Georgia bookstore, Athens. Phone: 706-549-3081.
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