I used to work in a LFS when I was a lot younger. I remember they used to have a massive aquarium which acted as the counter, it was at least 6 feet long and 4 feet high.
In the tank, they had a massive Clown Knife Fish which was easily 2ft long and a Red Tail Catfish which was roughly the same size if my memory serves me right. Where it was so big, obviously the Clown Knife didn't do an awful lot of darting around; it liked to hover around at mid level for long periods. I really loved the markings of this fish and the way its tail ripples when it's hovering.
We used to feed these live goldfish, normally fancies as the shop had an abundance of these. The cat used to swallow them whole, whereas the Clown Knife used to sneak up behind the fish and take it's back end clean off and then go back for the rest.
I'd love to get one, but I haven't at this point in time got any suitable tankmates. I've got a community tank at the moment, but that might change soon!