Oh, this is FUN!! Go get a bottle with a narrow neck, small mouth and fill it to the very tip-top with water. Place an index card over the mouth of the bottle and hold it on tightly, not letting any air slip in, as you turn the bottle upside down. (Do this in the bathtub.) Then, slip away the index card and keep trying until you get the water to stay up inside the bottle. So, go do that and then come back..... we'll wait..... no don't read ahead.... go on.....
If no air goes up inside the bottle, the water will remain suspended inside the bottle (for a little while). That's the trick.
That bottomless aquarium implies that it is also topless, since the air bubbler is running, that air is going someplace, out into the room... or it would be filling up the "aquarium" with air, displacing the water, if the aquarium were sealed on top, right? Okay, so there is not a lid on the top of the aquarium....
So it isn't like the bottle trick. The bottle, once you turn it upside down, only has an opening at the bottom and not the top. If air doesn't displace the water inside, the water stays up there (for a little while) in the bottle. Not so this bottomless aquarium.
The only way the water would stay up in that aquarium is if it the system were sealed and no air could get in.... it ain't sealed and air is getting in (the bubbler).... you can't stand water up just because it has aquarium glass sides around it..... just what part of "gravity" and "liquid" don't you understand
Besides, the fish swim funny............