Can Trout See UV Light? The Answer Might Surprise You

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Close up image of trout's head.

Trout can see UV light, but only when they are younger and focused on zooplankton as a food source. As trout grow bigger and older, they lose the cones in their eyes that allow them to see UV light. Therefore, there’s no reason for you to use UV-reactive baits, flies and lures when you’re fishing for trout.

Trout eyes are UV-sensitive when they’re young. They lose this ability over time. 

Trout are hatched with the ability to see ultraviolet light, according to researchers, but their ability to see that light fades over time. 

Just like humans, trout have eyes equipped with rods and cones, which gives them the ability to see colors to varying degrees. But, as young fish — fry and parr — trout have the ability to see UV light. This helps them find zooplankton, the food they need to grow. 

As they get larger and start eating larger prey, like insects, worms and fish eggs, trout lose their UV-light sensitivity

So, as an angler who, presumably, is targeting adult fish, there’s no reason for you to worry about UV-reflective flies, lures or baits. It’s just not necessary. 

Why Does the Ability Fade?

It’s likely simple evolution, but nobody really knows for sure why trout lose their ability to see UV light rays. It might simply be because the ability becomes less necessary as trout grow into more predatory fish. 

For years, I spent hours at the fly-tying vise using UV-sensitive tying materials and even UV-sensitive resins. As it turns out, I was wasting my time.

By the time I used the flies to fish for trout, the fish I was after couldn’t tell the difference between UV materials and just plain old tying material. Bummer, right?

Seeing UV light rays at a young age shouldn’t be confused with a trout’s ability to see colors (they can see colors, by the way). Instead, the ability is likely associated with the necessity to see the very small zooplankton. 

Zooplankton are miniscule creatures, like newly hatched insect larvae, trout need to survive as fry and parr. These small critters reflect UV light, and small trout can see them. 

Since you’re not after small trout, there’s no need to use UV-reflective flies or lures. No sense wasting time and money on those materials, right?

Why Does the Ability Fade?

According to researchers, the eye cones in young trout that enable them to sense UV rays disappear over time. UV-sensitive cones are not present in the eyes of mature trout.

Instead, mature trout have very well-developed cones that allow them to blue light rays extremely well. 

This could be because blue light rays are short and can penetrate water better than other colors. Red, for instance, fades greatly in water 10 feet deep or deeper. Red light rays are longer and don’t penetrate water as well as blue light rays.

Nevertheless, blue light and UV light are not the same thing. When I fish streamer flies in deep water, I often use flies tied with a blue-hued tinsel that trout can see. When I fish in shallower water, I tend to use flies that incorporate red. 

But the UV lure or UV-reflective tying material? You don’t need it. Return it to the store and get your hard-earned money back!

If Uv Light Doesn’t Matter to Anglers, What Does Matter?

Man's hand with black glove holding a trout with bait on it's mouth.
Black flies and lures work well in low light and dark, stained water. Black blocks out all other light, making it easier for trout to see.

There are several colors of baits, lures and flies you should consider when you’re fishing for trout. 

If you’re after trout, you’re going to have better luck using flies, lures and baits in the red color spectrum. Trout see even drab reds as quite brilliant.

You can also enjoy success with yellow and chartreuse baits. On darker days or or in dirty water, anglers should consider black flies, lures and baits. Black blocks out all other light, making it easier for trout to see black flies and lures, even at night. 

Trout, too, are very perceptive of purple baits. Red and purple flies, lures and baits can be particularly effective in clear water. Red and purple are found in natural food sources for trout, like earthworms and salmon eggs.

As an angler, you are almost always going to be better served by matching the prey base that’s readily available for trout. In other words, “match the hatch.”

When I fish for trout in high, turbid water, I like to use fly patterns tied to mimic worms, because moving water often washes earthworms into the river or creek. 

When I fish during a prolific mayfly hatch, I fish with dry flies that look like the insects that are hatching. This makes perfect sense, right? And it has nothing to do with UV materials. Nothing.

Using UV-reactive flies, lures and baits probably doesn’t improve your chances if you’re after trout. The latest research debunks a long-held belief that UV light sensitivity persists in trout throughout their life cycles. 

That’s just not the case, and there’s absolutely no reason for you to invest extra money in UV-reflective baits, lures or fly-tying materials. 

Instead, you should focus on baits, lures and flies that mimic natural food sources. 

Final Thoughts

Man's hand holding a small trout with bait on it's mouth.
Sometimes, using fly patterns or baits that mimic natural food sources is more important that using lures, flies or baits in certain colors.

While it’s always been fashionable to pursue trout with UV-reactive flies, lures and baits, don’t fall for the hype. Mature trout can’t see UV-reflective materials, so there’s no need for you to use them. 

If you must choose a color that gives you the confidence to cast to trout, consider red and purple flies, lures and baits in clear water, yellow or chartreuse baits in tannic or stained water and black or blue flies in dark, turbid or deep water. 

There’s no need for UV-reactive materials in flies, lures or baits — adult trout don’t have the eye cones to see them. Instead, you should focus on “matching the hatch,” and fish with baits and flies that are present in the water or imitate the trout’s natural food base.


What Does “match the Hatch” Mean?

It’s a term used by fly fishers who try to match the color, size and silhouette of natural food sources for trout by tying flies that look like those food sources. 

For instance, a San Juan Worm is tied to look like a small earthworm or red worm. A Pale Morning Dun is tied to look like a pale, yellow mayfly that’s common on trout rivers. 

Can Other Fish See Uv-reflective Materials?

Yes, some fish retain their UV sensitivity as adults. Do your research on the fish you’re after and how they see light and color. This can help you be a better angler.

Is Color the Most Important Factor When Choosing a Fly, Lure or Bait?

There’s no doubt that color is an important factor. But, before choosing a fly, lure or bait, you should first consider what natural food sources are present in the water you’re fishing. 

And, if you’re a dry-fly angler, remember that trout will look at your presentation from below, meaning they will likely only see the fly’s silhouette. 

You should choose a dry fly that has a silhouette the trout might recognize. 

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