LionFish says......
Well, there is a very fine line between this subject. Technically if you keep a reef with inverts like shrimp and crabs you shouldn't get one. However, if you get large fish and have no shrimp and crabs then it is entirely possible. But you must remember that the smallest lion in the hobby is the Dwarf Lion which get up to 8 inches in any tank. You need a minimum of a 50 gallon tank and must not keep any small fish. Lions are very good predators so you can't pull anything by them meaning no small fish, no crabs, and no shrimp. If you meet all requirementts then it is possible. Any questions?