Clown knives are very beautiful, graceful, peaceful predators that are primarily nocturnal, but can be taught to feed during the dayling. But they are not reccommended for beginners because they do grow to immense lengths, sometimes topping three feet or more. They're primarily an ambush predator, although if feeling comfortable in their habitat, they'll seek out food.
The Clown knives I've had have always been babies, and they'll eat feeder guppies/minnows, and occasionally can be trained to a ciclid pellet, krill, or flake. Always gut load your feeder fish to make sure clown knives get the full nutrition from the meal.
They get along with just about everything that would leave them alone, and even though their an African fish, I have kept them sucessfully with Green and Gold Sevrums, Blood Parrots, and other relatively quiet SA Cichlids. I would not reccommend them with Pacu or other very fast fish since these may shy the clown knife into hiding all the time.
Things definately not to put with a clown knife are fish that are small enough to fit into his mouth, like neons and such.
Clown knives are also sometimes called Featherbacks, or Featherfins, so check these two ailiases when looking for information as well.
~~Colesea