The crowned squirrelfish is an interesting fish, but it requires some special considerations to be kept in an aquarium. First of all, as you can tell by the size of the eye, this fish is primarily nocturnal. This means that they do not like the bright lighting of many marine aquariums, and regardless of the lighting they require caves, overhangs and the like where they can hover during the daylight hours. They also prefer to be in the company of others of their species, which means that they really need to be kept in a very large tank.
If you can provide them with a large enough tank, conspecifics, and plenty of places to hang out in, then the crowned squirrelfish is very easy to take care of. They will eat just about anything, and the best foods to present to them are chopped fish, clam or shrimp as well as any of the prepared frozen foods. They may take a long time to become adjusted enough that they will come out and feed during the day, so at least initially you need to feed them when the tank lights are just going out. Having a moonlight phase for the tank lighting is extremely important with this fish, as they will not become active in total darkness.