My husband has two tanks of fish (one 60 gallon and one 75 gallon.) Right now there are mainly african cichlids in each tank. One tank was originally set up with salt water but he changed over to fresh water. At the beginning of this hobby one of his early tanks had south american cichlids. We had two very large oscars (about 7" long) who would come up to rub along his hand when he was wiping the inside glass down, very similar to how a cat rubs against you. He in turn would pet them. When it's feeding time they would splash and splash (wigging their little bodies like an excited doggie!) They really were very bright! Occasionally he would give them a piece or two of dog food kibble which they thought of as a treat! Our kitties love to watch them and by now the fish are used to the cats and know that they can't be reached by kittie paws!