Direct Sunlight From A Low Sun
I have, for some time now, a couple of goldfish.
They are healthy and active.
Since I moved the location of the aquarium (the light source) has changed.
Now, during winter, there is direct sunlight from outside coming into the tank.
And the thing I worry about is whether or not this damages their retinas.
I live in the Netherlands so the low standing sun isn't too intense but still, I shield them from it.
It takes somewhere between 2 to 3 hour for the light to pass.
Are my fish in danger of getting blinded by that?
The aquarium its self is roughly 8 to 10 feet away from the window.
I have no problems with algae or anything.
Thanks for your time. Hope to hear from you soon.
I haven't read any reports referring to sunlight causing damage to a Goldfish's retinas.
There are two varieties in particular that would be very susceptible to damage and they are the Celestial and Water Bubble Eye.
Both these varieties have eyes that face upwards, and over the millennia that they have been bred, there would have been some reference to protecting their eyes from sun damage.
I have bred both varieties and have never given them extra protection from the sun. None of my fish ever developed cataracts that it is believed can result from UVB light damaging the eye lens in humans and other mammals.
The other important fact to consider is UVB light doesn't penetrate glass, only UVA does.
Experiments have been done subjecting juvenile Goldfish to massive doses of UV light, but these amounts were far in excess of natural light. I don't believe your fish will be unduly harmed by 2-3 hours of direct sunlight.