Guppies Eyes

[Odie]

I have 5 surviving guppies, about 3 months old that I inherited from a first grade teacher's classroom science project. I have noticed that at different times the guppies eyes seem to be completely black, and it almost looks like the blackness shows internally under the eye also. The next morning the eyes look perfectly normal with small black area surrounded by silver ring. Any ideas on what is happening? Thanks!

 

[*Fishkies*]

I have noticed that also with guppies. Not exactly sure what that is. Maybe it's how they prepare to sleep at night.