Color Vision in Trout and Salmon

by Gary Borger

Publisher's note: I'm tired of looking at Gary Borger pictured with very large trout. So instead we're improving our artistic content with Jason Borger's lovely lithographs.

Color vision is a well-defined trait in shallow-water fishes of both oceanic and fresh water systems. It evolved, as it did in other animals, as a mechanism to allow the fish to better separate potential food items from the background. In the watery environment, the background may be either the bottom (normally a tarnish olive to green color) or the background may be the water itself. When looking horizontally through clear water, the background appears pale, silvery blue. This phenomenon is known as background space light and is caused by the scattering of blue light as it passes through the water. In water with a lot of suspended algae, the background space light is greenish yellow, and in tea-colored bog water, the background space light appears reddish brown.

"Three Domestics and an Import" The brook trout, the rainbow and the cutthroat are the natives, the brown is the import.

Lithograph 1 by Jason Borger

Thus, for opportunistically feeding trout and salmon, flies or lures with strong coloration and/or a lot of flash--which makes them stand out strongly against the background spacelight--are great fish attractors. The red and yellow Mickey Finn bucktail is as effective today as when introduced to the angling community by John Alden Knight a half century ago, and the Royal Wulff is such a great dry fly because its white wings and iridescent peacock herl body are easily seen by both fish and fly fisher. Fluorescent colors stand out strongly against background spacelight of any color, and fluorescent shades of reds, oranges, purples, and chartreuse are highly attractive to salmon and trout.

Anyone fishing for steelhead or migrating salmon is well aware of the attractiveness of lures of these colors. And anglers fishing "glo-bugs" have discovered that trout will take them readily at any time, not just during the spawning migrations. Black lures and flies can be very effective also because they have such a strong silhouette. Silver lures, or flies constructed with tinsels or materials like Flashabou, sparkle and flash when retrieved because they strongly reflect all light that falls upon them. Below about fifteen feet, where the light level falls off sharply, fluorescent and highly reflective lures and flies are most effective.

Night anglers often differ sharply on the color of the lures they most prefer. Since they all catch fish, they must all be right. The truth is, when the light level falls below 0.1 foot candle (a typical star-lit night without a moon) all colors become just shades of gray. White still looks white, however, and I like it for top water lures because I can see them. Anglers fishing for king salmon in the Lake States report excellent success with subsurface, phosphorescent lures that glow in the dark.

For selectively feeding trout, color not only serves to separate the food organisms from the background, but also serves as one of the four major characteristics that triggers feeding (the others are size, shape, and behavior of the food item). Thus for the fly fisher, color becomes a necessary consideration when choosing the best fly to match a natural food item of selective trout.

The question then becomes, how accurate does the color match have to be? It was a question that started me on a twenty-year experiment into the color preferences of selectively feeding trout. First I assured myself that selective trout are definitely sensitive to colors. They can and do distinguish between brown and olive, for instance.

In response to the obvious question raised by this result, I found that even though trout can distinguish colors, they do not discriminate between very fine shades of any one color for selective feeding purposes. The reason for this lack of color hyper-sensitivity is simple: the food organisms vary slightly in color. If the fish were too color sensitive, much food would be lost. For selective feeding purposes, trout will normally discriminate between about four or five shades of a color, from the palest shade to the darkest.

I also discovered that when matching some insects, a shade of a color different from the shade of the natural can be more attractive to selective trout; usually the more attractive shade has more chroma (the color appears more intense than the color of the natural). The reasons are complex and not completely understood. For one thing, the food organism is often multicolored, and one of these colors might stand out more to the trout than other colors. Trout see further into the ultraviolet range than do humans and perhaps are seeing a "color" that is not visible to us. Then, too, the watery environment could be influencing the transmission of specific colors. In addition, skylight varies during the day. In morning and evening, for instance, skylight contains more red; therefore, at these times reds, oranges, and browns will stand out more than other colors. There's still some very interesting work to be done in this area.

Pay attention to color when selecting lures or flies for trout and salmon; it could keep you from getting a case of the fishing blues.

Gary Borger - Tomorrow River Press bar