lionfish are a marine fish and needs a fully cycled marine tank.
they are also predators and will eat any small fish and crustaceans.
they also have spines that are venomous.
they do best, but not solely in a species tank(a tank specific to one fish).
I would not suggest getting one until you've had a lot of experience with Saltwater. They are highly venomous and dangerous to care for. While it won't kill you to get stung, it will require a trip to the hospital. They also are somewhat difficult to care for compared to Freshwater.