What Trout See

Photo by V. Loftus, all rights reserved

Photo by V. Loftus

A recent April spring afternoon left me in a state of pure bliss: I had landed 28 trout during an explosive bite. Wanting to determine if the nonstop action would be impacted by the color of the fly, I tested five different seal bugger colors: olive, orange, white, black, and burgundy. Which color do you think was the most productive?

Surprisingly, all colors worked! No matter the color of fly, repeated takes were like being hit by a freight train. Rainbows launched out of the water completing multiple five foot aerials. Yet other times I have found trout can be very finicky in what they take. Understanding how various factors affect light and what trout see will help us refine our presentation and increase our angling success.

Photo by V. Loftus, all rights reserved

Photo by V. Loftus

Time of day
The amount of light that penetrates the water can vary based on the time of day due to the angle of sunlight penetrating the water. On this recent spring day, when trout looked up towards the surface of the water, the high overhead position of the sun meant the fly could only be viewed as a silhouette. The bright sun’s position midday made it impossible for the trout to distinguish the fly’s color. This is because the smooth, glassy conditions allowed more light to penetrate into the water column causing the flies to be backlit. Trout keyed on the movement of the dark silhouette and less on the color. During midday, when the fly is the same depth of the trout, then and only then is the color distinguishable.

In low light periods such as dawn and dusk, feeding trout will often hunt closer to the surface where they have a smaller field of vision. When fish are deeper, anything above them is seen as though looking through a cone. The deeper they are, the wider their field of vision. When they are closer to the surface, the more restricted and narrow their visible window. If the angler is outside the range of the trout’s visual window, the trout will not be alerted to the angler’s presence.

When sight casting, trout will be just below the surface and color will be more critical. In such conditions, you must be precise with your fly placement in order for it to be seen. Place the fly far enough ahead of the cruising fish to attract it, but not close enough to frighten it.

When trout are feeding near the surface or even in the film, their viewing angle is small and tight and they can see detail close up. This allows anglers to approach feeding fish much closer and not be noticed compared to when fish are holding deeper. When trout are holding deep, they have a larger viewing window of what is above them, including the angler. Long casts keep the angler outside of the trout’s viewing window, which avoids spooking the fish.

Photo by T. Loftus, all rights reservered

Photo by T. Loftus

Depth of Water
In clear and shallow water, colors will be more recognizable in the top few feet. However, three to six feet down, colors become muted as less light penetrates the water column. Additionally, since water is denser than air, light bends when it hits the water. Light becomes scattered and colors change, and become subdued. In clear water, red and orange (colors with long wavelengths) are absorbed first. Colors with shorter wavelengths (violet, blue and green) remain visible as darker silhouettes.

Dr. David Ross, explains in “Fish Eyesight: Does Color Matter?” how color selectivity becomes less critical when fishing deep. At 10 feet, roughly 60 percent of the total light will be absorbed. This causes the color of the fly to appear gray and eventually turn black as the depth increases. Absorption of light and the filtering out of color wavelengths also effects vision horizontally through the water. If the fly is a few feet away horizontally from the trout at a deeper water depth, the fly will appear grey. To get a better idea of how this would appear to the trout, view these seal buggers in black and white:

Photo by T. Loftus, all rights reserved

Photo by T. Loftus

Photo by T. Loftus

Stained Water
Imagine looking through green tinted sunglasses; some colors will be stronger while others subdued. In the same way, colors seen by the trout are affected by particulates in the water. For example, a burnt orange fly in green algae stained water will appear orange/brown. Additionally, since there is less light in heavily stained water, dark flies produce a clearer silhouette and are therefore easier to see and more effective in such conditions.

Trout Vision
Trout and human eyes have many similarities. Both share lens-covered retinas that contain rod and cone photoreceptors. Rod cells perceive contrast in low light, cone cells provide color vision. The trout’s cones are tuned to colors: red, green and blue – the same as the human eye.

One difference is that trout do not use rods and cones at the same time, the way humans do. Trout cones are activated only during the day so trout can see color while the sensitive rods are disengaged to protect them from bright sunlight. At night, the trout’s cones disengage and the rods activated to see in the dark. Since the trout cannot see color at night, they rely on contrast and key on the silhouette.

The only time that trout activate both their rods and cones at the same time is for a brief period during dawn and dusk. Small prey have two-toned bodies: dark on top and a lighter belly. Flies with a darker upper and lighter underside replicate the appearance of natural prey. This is why minnow patters are so successful during dawn and dusk as they offer an appetizing silhouette to feeding fish.

Do fish see UV light? Debate continues…

Photo by T. Loftus, all rights reserved

Midge Pupae, Photo by T. Loftus

Whether or not to add UV materials to a fly is an ongoing debate in the scientific and angling communities. Some researchers say young juvenile fish still in the Parr stage have the ability to see UV light and which later shifts from ultraviolet to blue. Others say that the ability to see UV light disappears by the time the trout is two years old. Still others believe that certain species use UV for only a part of their life cycle. Some researchers counter that trout retain the ability to see UV light into adulthood.

It is up to the reader to decide if UV seems to make a difference based on their own experience. Personally, I have found that in heavily stained water, the flash of iridescent UV material can add contrast and increase the fly’s visibility. However, an excessive amount of UV flash can spook trout on bright clear days.

Remember, in stillwater all living food sources that trout pursue emit UV light. Can trout see it? Or do they rely on silhouette and movement?  You be the judge.

Conclusion
As anglers transform a simple hook wrapped with material into something appearing to be living, breathing, and tasty, we select our favorite colors based on personal experience. However, those colors will be perceived differently depending on the time of day, position of the sun, and the degree of light penetration in the water.

Tips:

  • Sight casting requires precision: place the fly ahead of the trout in order for the fly to be seen.
  • When fishing deep with chironomid patterns under an indicator, choose a dark fly.
  • In low light or stained water, select flies with contrasting colors and/or darker colors.
  • Try various colored flies when angling on sunny days in shallow water to determine whether there is a color preference.
  • When the sun is high, any color in your fly box should be equally effective.
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