Sunlight affecting the fish?

Ok - here's something I never thought about - does the amount of direct
sunlight affect the way the fish act. I have a passive solar house (sited
to take advantage of the winter sun to heat the house) and now the tank gets
direct sun for a several hours during the AM; something it doesn't from
March (when I moved the tank) to late November. Since November, the fish
(especially the larger of the two) get real quiet in the AM and get active
again around 3 PM - after the sun is past the house. Cloudy days, they are
as active as in the late afternoon to early evening. No matter what, they
do start begging if you approach the tank.

Should I be shading the tank some?

Now, I am fairly sure there is a direct correlation here. Sunny days=quiet
fish, cloudy days= active fish.

Thanks for you time

Cheryl