Ponderings

I would imagine fish can see each other due to the fact that bettas in containers next to one another will flare at each other. Also, I fill my water up to the point that I can't see the water line anymore. It doesn't really matter how high you fill it, it is really just a matter of personal preference. The water splashing out of the filter isn't a bad thing and it will add more O2 to your tank.

I believe that the fish can see each other if the tanks are very close. Think about it. When my fish see me coming close to the tank, they gather close to the surface because they think it is time to eat. They associate me with the food that they are getting. So I would say that yes they can see other fish in close proximity even if it is in another tank.

About the water level, I think it is just a matter of preference. Myself, I don't like to see water levels so I fill the tank's water just above the rim so I do not see any water levels. If the water levels are lower the filters make more noise which some people don't like, but it will offer more oxygen for the surface via more aggitation of the waters surface which allows more oxygen to break at the surface. So, It's up to you and what you prefer in your tank. I hope this helps.

Marinemom

this is so strange. i was just wondering the same thing today. i recently (sat.) got some fish for my planted tank which is right next to my dempsey's tank and he has been staring out ever since. and he never stays on that side.

so i'm thinking that yes they can .

My fish come to the glass and look at me when I come near the tanks all the time, so I assume they can see into another nearby tank.

When breeding cichlids it is fairly standard practice and has been for years to line up the tanks of similar species. The males can vent/release their aggression by guarding and displaying to the males in adjacent tanks rather than their females. It reduces or eliminates the need for dithers/targets. Of course, you do have to keep the end glasses clean.

That dates way back to Konrad Lorenz work, Read his popularization, King Solomon's Ring" sometime.

my betta at work can see me from across my desk (5 feet) he gets excited when 'visitors' stop and look at him. If he sees me come back from lunch and i dont feed him right away he will bump the tank until i look at him then he will flare at me. then i tell him "what you looking at fish-face"

so yes i imagine fish could see each other from atleast 6-8 feet.