How Bad Is It?

In 2010, scientists named the lionfish one of the top threats to the world’s biodiversity. In some places, lionfish have reduced native fish populations by 80 percent. How is that possible?

Unlike many other fish, lionfish never say no to food. They can eat one to two fish per minute. Over a year, this works out to hundreds of thousands of fish eaten by lionfish.

They feed mostly on small fish. Yet, lionfish can wipe out entire groups of crustaceans, such as shrimps, too.

They also eat the young of larger fish. This makes it hard for some species to rebuild their population.

A lionfish swims near a mangrove forest.

New Rules

Lionfish behave in unexpected ways. This makes them more dangerous than most predators. Here’s an example. Mangrove forests have always been a safe place for young reef fish. These stretches of sea between rivers and oceans are brackish. They are a mix of freshwater and saltwater. Most ocean predators don’t hunt there. But the lionfish hunts there with ease.

Lionfish disrupt reef behavior, too. For example, certain cleaning stations there are “safety zones.” Larger fish line up to get parasites picked off of them by smaller fish. The cleaner fish get an easy meal. The larger fish get clean and enjoy better health.

This young snapper is being cleaned by humpback cleaner shrimp.

Part of the bargain is the larger fish don’t eat the cleaner fish while the work is being done. But lionfish don't follow that rule!

Fish aren’t the only living things threatened by lionfish. Many reef corals are also under attack. When lionfish eat too many plant‑eating fish, there’s nothing to eat algae. So, algae grow out of control. Algae cover the corals, choking off light that corals depend upon. The corals die. This leads to a loss of habitat for other reef creatures.

These lionfish crowd together on one coral reef.