Lionfish were first reported off Florida in the mid-1980s and were established along the southeastern United States by the early 2000s. Analyses of mitochondrial haplotypes in the Atlantic population recover only a handful of distinct types, far fewer than in the native Indo-Pacific range, which is the signature of a founding event involving very few fish.
The expansion has been fast because the biology suits it. Females spawn buoyant egg masses roughly every few days year-round in warm water, the larvae drift for weeks, and Atlantic reef fish have no evolved recognition of lionfish as a threat. Native predators rarely attack them, and their venomous dorsal, pelvic and anal spines make them costly to try.
The usual dramatic framing, that Hurricane Andrew in 1992 released the founding fish from a broken aquarium, is not supported: confirmed sightings predate the storm. Culling programmes and targeted fisheries reduce density locally but there is no evidence they can reverse establishment at regional scale.