I used to wonder if trout saw colour. Then I did some research and found out that they do as their eyes are similar to humans. Interestingly enough, although they do see colour, the very idea of colour being seen at different depths is another matter.
I memorized the initials ROY G BIV (more on this later) as a method of remembering which colours held true to certain depths. If you remember your science from school you know that colour is the visual perception based on the wavelengths in the electromagnetic spectrum with violet being at the ultraviolet end of the spectrum and red being at the other end known as the infrared spectrum, specifically, this is the portion we see or perceive as light reflected or emitted by objects. According to Britannica, colour is described by hue, lightness, and saturation. It must be further noted that colour is not an inherent property of matter, but rather a result of how our eyes and brains interpret the wavelengths of light.
Ron Newman, in his book “Rainbow Trout Fly Fishing” dedicates an entire chapter to sensory perceptions of Rainbow Trout. This includes what fish see. He notes that rainbows are primarily sight feeders despite the fact that they are near-sighted, with a maximum visual distance of five meters during optimal water conditions.
Another piece of information I found indicated that trout can detect four spectrums of light: Red, Green, Blue, and Ultraviolet. But apparently, the ability to see in the ultraviolet spectrum fades after a couple of years.
What I memorized was the colours that changed first as they descended into the depths of fresh water. Basically, the colours fade into differing shades from grey to black.
Referring to chart 10, provided to me by Ron Newman, one can see how colours fall out of the visual spectrum as a colour descends in the water column. What is important to note is that optimum light penetration is when the sun is at the apex and the water is the clearest. It goes without saying then that sunlight, at either side of its peak, penetrates less and of course the colours fade more quickly.
Looking at the chart it is easy to see where the acronym ROY G BIV is derived as it relates to the colours that fade first from the spectrum underwater, with red being the first and violet being the last. The importance to the angler then is knowing that red, for instance, on a bright clear day with the sun directly overhead, begins to fade at a depth of three feet (one meter) and has changed to either a grey or black shade at 15 feet (five meters).
The rest of the colours follow suit at differing depths, with violet retaining 87 per cent of its original colour at 24 feet (eight meters). It must be kept in mind that this is the optimal sunlight penetration, and anything less, such as sunrise, sunset, or clouds will change this.
Using this information, the angler can decide which colour may be most visible to a Rainbow trout at any given time of day depending on the water clarity. Of interest may be that ultraviolet rays are not altered by cloud cover. I interpret this to mean that the violets, indigos, and blues remain somewhat more visible despite a cloud cover to various depths while colours at the infrared end of the spectrum are impacted on cloudy days.
While chart 10 provides some intriguing information, I think that more research is needed to fully understand just what a fish actually sees. It is common knowledge among kokanee fishers that they seem to prefer pink for some reason.
Trout in shallow water can see greens well, so a green shrimp pattern is quite productive. I am still unsure of why a bloodworm pattern fished at a depth of six meters or more will catch fish consistently. It is my guess that the fish do not see it as red, but merely as a representative shade of the bloodworms (Chironomid larvae) they have been feeding on. At least, that is my opinion, so don’t take it as a fact!
What is important to note is how colours are impacted by depths, light, weather, and time of day. Since I do not have all the answers, I will leave it up to the reader to do some experimenting with colours throughout the upcoming fishing season.
