Lionfish eat fish and invertebrates. Juveniles eat mostly invertebrates, with fewer fish in their diet; adult lionfish eat mostly fish. They have been shown to cannibalize each other in the wild, with larger lionfish eating smaller lionfish. Their eating habits disrupt ecosystems by competing with native fish and overfeeding on species that control algae.

Lionfish are native to Southeast Asia, but are an invasive species in warm waters all over the world. They are of particular concern in the United States and the Caribbean, where they lack natural predators. Lionfish are found as far south as Venezuela and as far north as North Carolina. Cold winters inhibit the lionfish's permanent spread further north or south, though they are reported as far north as Rhode Island during the summer months.

In addition to the destructive effect they have on ecosystems, lionfish are aggressive towards both other fish and human divers. Lion spines are venomous, and in extreme cases can cause an extreme reaction in or even kill an adult human. Despite their venomous spines, lionfish are edible when filleted and cooked properly. The National Oceanic and Atmospheric Administration encourages the fishing and human consumption of lionfish in the United States, as this is the only form of lionfish control known to be effective.