Interaction, their awareness of what is outside the tank.
You can train them!
I have my 7" umbee taking it's pellets from tweezers held an inch above the water.
The crazy swimming up n down the glass when you get home.
My fish all went weird n started hiding coz I shilted a table and chairs, heheh, they definitely observe me.
If I am on the other side of the room, they will chase each other but if I turn my head and look straight at them they stop, like naughty puppies.
J
