UV Vision in Fish: Match the Ultra-Violet-Hatch (Article 1 of 2)

UV Vision in Fish: Match the Ultra-Violet-Hatch (Article 1 of 2)


I get it, you can't ‘see like a fish.’ For that matter you can’t experience what other humans ‘see’ either; and yet we take for granted that it’s probably similar to our own experiences (most of us have trichromatic vision and are able to see plus or minus a million [1,000,000] colors). We’re the same species after all. But, what about People who can only see an assortment of ten thousand (10,000) colors, who are born color-blind (aka Di-chromatic, meaning they see using two primary colors only)? 

And what of People with superhuman vision who have four primaries (i.e. Tetra-chromatic vision) and see the world through the lenses of a hundred million (100,000,000) colors? They describe what you and I would call a grey pebble path as vibrant with all sorts of colors. You don’t support the idea that their experiences are the same as yours. Why not? The answer of course lies in the Science of it all. 

The Human eye possesses Rods and Cones. Rods allow us to see contrast in low light (think dusk till dawn) conditions. Colors basically fade to shades of grey during low light so being able to have better perception of contrast is king. 

Cones on the other hand allow us to see colors (think ROY-G-BIV). When some of these cones are damaged or missing this can lead to what we have termed color blindness. For example, if you’re color blind, Greens and Reds may look the same. There’s an easy test for this developed by S. Ishihara, see below. Do you see a number? If not, you could very well be missing some cones for Greens and Reds. 


So, Rods and Cones, there you have it. Well, that’s only half the story. The eyes of other animals possess systems of Rods and Cones as well. Like humans, some fish are missing some Cones, but most fish have a far superior assortment of Rods than we do. Meaning, they are experts in contrast. If you’ve ever fished with a Black or Black and White spoon in green or murky water you know this fact all too well since you no doubt caught fish. A black spoon in turbid water stands out to a fish like a black dot on a white wall! 


 This isn’t only because Fish have more and better Rods. It’s also because Fish (most) also have the ability to see Ultra-Violet (UV) light. UV light creates an even starker contrast between objects and their background. The pictures above are identical still frames of images in turbid water. The one to the left you’ll recognize, as Human vision. The one to the right you won’t, its UV/fish vision. If your ancestors had evolved in murky waters and needed to be able to find prey to survive you would probably have UV vision too :). 

There are plenty of examples in other species as well. Bees, for instance, have excellent UV vision and flowers in turn coevolved UV color patterns which proved useful for pollination (Chittka et al., 1994; Kevan et al., 2001). Similarly, various fruits and berries that are disseminated by birds with UV vision also reflect UV light, but not until they ripen (amazing). Ripe fruits that are stripped of their UV reflection capabilities in laboratory research studies are eaten far less often (Altschuler, 2001). Reindeer also have UV vision and browse on lichen and moss in dimly lit Arctic conditions. Because these plants reflect UV light they contrast against “white” snow and are easily seen and eaten by these deer (Tyler et al., 2014a). 

Mentioned above, humans have Trichromatic vision. This means we have three primary (Red, Yellow, and Blue), and three secondary (Orange, Green, and Purple) colors in our visual spectrum. These, a total of six, comprise our Basic colors (Indigo is not a color, it’s the Pluto of colors, Google its history and definition, it’s fascinating). Objects and light (waves and matter/stuff) that we see as the color white and as white light are composed of all three primary colors reflecting simultaneously. 

This is precisely why Sunlight isn’t seen as Black rays of sun or Blue, or Red, or Yellow. Rays of sun are white (no sunlight isn’t clear, it's white, and before we get caught up in the minutia of the argument consider the snowflake. A snowflake is transparent white, the sum of all snowflakes are white, white since they’re no longer transparent in mass) because they are comprised of all color in our visible spectrum. Similarly, white objects are composed of all of the colors in our visual spectrum and therefore reflect all colors, thus appearing white. Black objects, on the other hand, are comprised of no color. Black objects therefore absorb all color, thus reflecting no color. 

If I haven’t lost you yet this is where things will get a bit more abstract. Many animals, including many fish, have Tetra-chromatic color vision. This means they have four, not three, primary color cones. Tetra-chromatic color vision, having four primary color cones, requires a combination of four primary colors within an object before the object is the color white (i.e. seen as being white). In other words, four primary colors comprise the color white, not three like with humans. Any clue what the forth color is? Hint: This article is about UV vision. 

“Until 1990, only a few animals were recognized as being sensitive to UV light, but we now know that a great diversity, possibly even the majority, of animal species can visually detect and respond to it.” Journal of Experimental Biology, - Thomas W. Cronin, Michael J. Bok. 

Human eye lenses, unlike the eye lenses of other animals, don’t allow Ultraviolet light to penetrate the eye. As UV light pertains to vision under water the research is quite remarkable, “…(UV) intensity remains in clear water to sustain vision at depths of 100m (up to 300ft) and beyond.” - Losey et al. 1999

Like Bees to flowers and birds to ripe fruit, the eyes of a fish not only allow UV light to penetrate through their lenses, but the scales of fish reflect UV light! This is an important finding for fans of Sportfishing and lure manufacturers alike. It bears repeating… fish scales reflect UV light (A ‘white’ lure attempting to mimic the underbelly of fish won’t appear white, more gray and muted, without the addition of UV properties). 

In feeder fish UV evolved through sexual selection where more vibrant mates were preferred. In Pelagic and other predatory fish nearer the top of the food chain, UV vision evolved out of necessity, it would seem, in response to those with the trait being more successful in targeting said feeder fish. In other words, those Predator fish that had the genetic mutation that allowed for UV vision, the ability to pick out and pick off prey, were able to find food sources easier and therefore passed their genes onto more offspring (just like in birds with UV vision and just like in Bees). 

A final argument for UV. My personal favorite lure color combination is Purple/Chartreuse. I’m willing to wager that at least one (1) of your top five (5) lures have a shade of Chartreuse (Yellow-ish Green) in them. It’s because chartreuse works (Five of Diamonds, Lemon-Ice, Coyote, 57 chevy, Baycity Bruiser, Gorgeous George, the list goes on and on and on and on), it catches and keeps on catching. It doesn’t matter if you’re fishing for Bass, Walleye, Brown Trout, or Salmon. Here’s the thing: What we see as the natural color yellow is actually made of two perceptually different color spectrums (if you have 4 cones and tetra-chromatic vision). If you were a fish you would visualize both yellow and UV‐yellow. Again, the color yellow naturally has UV properties embedded in it. You’ve been using UV lures and catching throngs of fish, possibly without knowing it. 


Happy fish and Tight lines. Welcome to the Evolution,

Article written by Mike Hiller

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