F.W. Lionfish are really cool, I've kept a couple in the past. They don't call 'em lionfish for nothing as eventually you will hear a strange growling noise coming from the tank in the middle of the night and it will be the lionfish. They don't do it that often but you'll hear it if you're in the same room or close by. Mine refused anything but live feeder goldfish and maybe nightcrawlers if I recall. I have read that they are somewhat of a brackish water fish and survive longer under brackish conditions but I kept mine in pure fresh water before I knew better... Yours looks really healthy, nice!
This species is best suited for a saltwater or brackish water tank containing tank mates that are too large to fit into its cavernous mouth. It can only be kept in fresh water for a short time, but it cannot be permanently maintained in freshwater as it will not live for long. Acclimate them to a brackish tank slowly, over a period of about a week. A heavy brackish water of 2.5 % to 3% salinity (density 1.020-1.024) is suggested.
Provide a minimum tank size of 40 gallons or more for a juvenile. Larger fish will need much more room with 100 gallons or more being best. A gravel bottom along with rock caves to provide some hiding cover is recommended to keep one in good condition.
Make sure to do your research guys. They are not freshwater at all.
I had seen one in the LFS myself years ago and inquired about it. The second I heard brackish I changed my mind. Since then I've seen them on tv in saltwater.