They are gulpers, so anything that it can fit in its mouth it will even if it is only able to eat half the fish. Obviously they are venomous, they like low flow and don't do well with aggressive tank mates like triggers. Most unless they are of the dwarf variety will get over a ft in length and become more difficult to feed, unless you like using a entire pack of frozen food for each feeding. The damsel may live for awhile in the tank but he also will become a snack for the lionfish. They are also dirty fish, not as bad as triggers and puffers as far as biting off food and spitting chunks into the water column but a oversized protein skimmer is a must