I've recently discovered the ability to visit other Aquariums and feeding other's fish. I know I get coins for doing that, but so far while I can't really tell, I don't think anyone has visited my Aquarium.

How can you tell if someone visits you, do you get some sort of notification or something?

When they do visit you, and they feed your fish, do you yourself get anything?

Lastly, what exactly are the benefits of the visiting?