Sun's Ultra Violet Rays and TroutIt 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
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:
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.
Hedley's Trout Farm