Lionfish are non-native and invasive to the Caribbean Sea.
A fish species is considered invasive if its position in an ecosystem negatively impacts other species. Generally, these are non-native species which have been introduced into a region by humans (either intentionally or unintentionally) with detrimental consequence to resident fish and other aquatic organisms. However, some argue that a native species can also be considered invasive if humans have altered its natural ecosystem to the point where the species can throw the whole system into disequilibrium.
For further information, please check out a related post on The Fisheries Blog – Blurred lines: Can climate change-induced range expansion qualify a species as invasive?