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There was news recently of the discovery of a gene in some trout and salmon that apparently will allow those fish to change color at will, much like the famous chameleon. As reported in the online journal, Medical Daily, some trout can change color to better match whatever the background happens to be at the moment. All trout fishermen know that those fish can be very hard to see sometimes, even in clear water, so that’s partly the reason why.

What’s most surprising to me is that this color-change phenomenon has been so little described–almost never, actually–in the hundreds of books devoted to trout fishing. And I think the reason for that is because while trout fishermen might have seen it happen, they haven’t realized what it is they’re actually seeing.

I have only encountered this once, at least that I could see in a definitive way. Many years ago, I watched a brown trout in a clear, sunlit pool. The fish had distinct zebra-like bars on its sides, a perfect match to the pattern of shadows on the pool’s bottom. I caught the fish, and by the time I landed it the bars had disappeared. It was really weird, and I passed it off to an optical illusion on my part.

Years later, I read a research paper by one Thomas Jenkins, who as a biologist in California in the 1960s had spent thousands of hours observing stream-trout behavior from an elevated platform. Jenkins noted such color changes in both brown and rainbow trout, with brown trout showing the most dramatic changes. As Jenkins described it:

“General lightening and darkening of [skin] background color in response to varying bottom colors and light intensities was observed in both species, but the change was slower and less extensive in rainbow trout. In addition to lightening and darkening, the ability to produce various mottled patterns has been ascribed to stream-living trout…I observed this type of response of pattern to background in many brown trout, but never in rainbow trout…”

Jenkins went on to note that such color changes in brown trout could happen in as little as 30 seconds.

In recent years, I’ve seen this mentioned very occasionally on various Internet bulletin boards when anglers have noted seeing an odd-looking brown trout. The response among commenters at that point has invariably been denial, that the original poster was confused as to what species he was seeing, and various other explanations–all but the right one.

But that chameleon-like change among brown trout is in fact true, however seldom described. And my question to you is whether or not you’ve ever seen it happen….

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