How can they see threw a pitch black glass.?

Question

HI i have two fish two male so i seperate them with a pitch black glass. One each side of the tank with a pitch black piece of glass in between.

Now this is what i dont understand, they cannot see threw there, not even a shadow goes threw.

Yet somehow, they know the other one is there. And want to fight. How is it possible.

Thank you very much
Muhammad

Answer 1

I bet they aren't seeing each other really. I think that once the glass is wet and standing in the tank they are each seeing their own reflection and wanting to fight it.

MM

Answer 2

yea, black glass is almost like a mirror