I remember tall,hexagon shaped tanks were popular in the early '80s-one setup I saw in a pet store back then was two hexagon tanks joined with two plexiglass tubes so fish could swim between the two tanks.
I remember those. I think they were made of plexiglass.
About the dog: We had a collie in the 50s that mostly stayed outside. When we brought him in though, he would lunge, nose first at the front of the smaller tank under the 10 gallon where he could see fish swimming. I did not know that dogs were that attracted to fish.
Yes, that's exactly what out Buddy does when he see's fish moving in the tank. I think it's the movement of the fish that gets him going. One time we were in a PetSmart and I kept him back from the fish tanks. He started making all these strange sounds at the fish, like he was talking to them.
In our home aquarium when I was growing up we had Discus fish. When you walked across the room they would follow your direction.
I remember reading something about modern aquarium care that recommended you change out 1/2 the water in the tank weekly. In a large tank that would definitely be cumbersome. It's supposed to help eliminate the ammonia and nitrates in the water.