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locate prey , primarily plankton . As these fish mature , the UV cones become less sensitive to UV and more sensitive to blue light , likely to aid in locating smaller fish and invertebrates which comprise most of their diet . Most anglers aren ’ t targeting juvenile fish , so is there even a case for using UV while fishing ? I think there is .
While many juvenile fish are hypersensitive to UV , there is considerable evidence that adult fish still retain the ability to see UV albeit highly reduced . Both humans and fish possess specialized cone shaped light sensors in our eyes that are tuned to particular light wavelengths . Humans have three cones that are sensitive in the red , green , and blue peaks . Fish possess similar cones , but these light sensitive cones also have a secondary “ beta ” peak of sensitivity that allows them to detect UV light even in the absence of a UV sensitive cone . This sensitivity to UV light in the absence of specialized cones has been documented in both the salmon family , including trout , and in the sunfish family , including bass . The degree to which these fish are using UV in locating prey has not been studied , but if UV reflectance allows my flies to look more like natural prey or entice a curiosity bite , I am more than eager to have it .
The vast majority , 95 %, of the UV light reaching the planet ’ s surface is UVA light . A smaller percentage is UVB . UVB is what gives you a sunburn , but also helps in the formation of vitamin D . However , UVA light is what fish are keying in on for visual cues . As mentioned earlier , UV light has a short wavelength . This property allows UV light to penetrate deeply into the water column like its corollary in the visible spectrum : blue . This is why the ocean appears blue , as it is the most reflected color from the water whereas colors such as red are absorbed in the top of the water column . This is why deep sea fish are often red in coloration as there is no red light available at depth , making the fish essentially invisible to predators . Water transmits light poorly so no matter what depth you are fishing , a UV lure is going to reflect a little more light , and that may just make the difference in low light situations whether fishing at depth , or at dusk or dawn .
Speaking of reflecting light , have you noticed how many UV products appear more vivid than their non UV counterparts ? This is because many UV reflecting materials are also rich in phosphors . These structures absorb light energy ( both visible and UV ) and reemit it as visible light . This is why a black light , which emits UVA light , makes UV material shine so brightly . The phosphors are taking the UVA light that you cannot see and reemitting in a spectrum of light you can see , they are like little light factories , and that ’ s the reason why phosphors are commonly added to many laundry detergents to make your whites whiter .
When looking for the maximum brightness , I always carry a small black light with me when inspecting flies and tying material . I am always going to select the material with the strongest fluorescence under a black light if I am going for brightness . Even if you don ’ t believe fish are using UV light in locating prey , the brightness argument is a compelling and brilliant one .
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