Big Malawi haps. They are some of the very few true open water freshwater fish. They will constantly swimming, and they are predatory. The fact that they like hard water makes them easier to care for for most people, and they tend to be pretty hardy. They are also true pursuit predators, something else rare for a freshwater fish. I wish I had a tank to put them in. Not my picture, but the fish on top, Champsochromis caeruleus, grows over a foot long.