Sun's Ultra Violet Rays and Trout

It must be stressed that what follows are only observations from a trout farmer who has operated a fee fish pond for more than 30 years.
Here is the dilemma:
It's a nice summer day's afternoon when tourist would like to take their family to a fee fishing farm but upon their arrival the trout aren't interested in participating. This is all rather embarrassing because the pond is well stocked and the water conditions are well within parameters - and  there are paying customers who know how to angle.
I though this situation may be unique to our location, but soon found other trout farmers experiencing similar concerns. At first we were sure that it must be the water temperature that was too high and the trout were lethargic due to oxygen starvation. Our meters showed that the dissolved oxygen was within acceptable levels and that there was no saturation of other gases. An operator located in the mountains of Colorado near Pike's Peak contacted me because he was perplexed over this same problem. I've talked to pond operators and owners of private ponds with a combined experience of many hundred of years

After eliminating water temperature and quality - what could be the problem? However, there was another clue right before us.
Even though the trout were reluctant to bite on the bait being used, once their 'normal food' pellets were broadcast onto the pond, these 'lethargic animals' erupted into a feeding frenzy. These were the same fish that bit well all day before when it was overcast and raining; in fact these same fish bit well earlier in the day (7-9:30 a.m.). So what was so different about this afternoon. We can only assumed it wasn't because of the sunny condition because we are open year around and have this particular trouble only in the summer months.
It became apparent that there is probably is a correlation between how well trout took the bait and the UV reading. There is existing published data that shows that trout do use some of the UV range.

Click here to see today's UV index MAP of N. America:
Conclusion:
After careful consideration, it is our opinion that a trout's ability to see is more acute as the UV value increases. It is further suggested that the trout are able to distinguish what is, and isn't, their 'normal food'. It is also apparent that the trout can observe people on shore much more readily on high UV days.

We invite others to offer their comments.
David Hedley
Hedley's Trout Farm