by Chris Patrick
Red Lionfish. (Jacek Madejski)
The lionfish (Pterois volitans) resembles a psychedelic fish-shaped peppermint, striped in red and white and decked with feathery, fan-like fins. But its venomous spines and invasive-species status make it much less innocuous than candy.
Lionfish are native to the Indo-Pacific. They’re popular aquarium fish—it’s likely ex-aquarium-owners introduced them into the Atlantic. They spread rapidly along the southeastern coast of the United States, into the Gulf of Mexico and the Caribbean.
Lionfish flourish in their introduced range, where they have no predators. They breed quickly—a female can produce up to two million eggs per year. They live a long time, sometimes more than 15 years. And they’ll eat basically anything that fits into their mouths, decimating populations of native marine animals with their voracious, indiscriminate appetites. When they arrive at a reef, they can reduce the number of native fish by 80 percent.
But lionfish may also be harmful to the native fish they can’t eat. A recently published PLOS ONE study reports that invasive lionfish are parasitized less than native fish.
Researchers, including Smithsonian Environmental Research Center estuarine zoologist Gregory Ruiz, Smithsonian Tropical Research Institute researchers Andrew Sellers and Mark Torchin, and Brian Leung of McGill University, compared the variety and abundance of parasites infecting lionfish and two species of native fish in Panama, the graysby grouper (Cephalopholis cruentata) and the lizardfish (Synodus intermedius). Lionfish, graysby grouper, and lizardfish are potential competitors because they use the same resources, preying on the same fish and living in similar habitats.
Ruiz and Sellers found parasites in Panama disproportionately infect native fish. There were twice as many parasite species and three times as many parasites total in the native fish.
Parasites also seem to damage the health of one native fish more than the lionfish. The researchers did not find a relationship between a lionfish’s health and the number of parasites it has, suggesting native parasites might not affect invasive lionfish. The more parasites infecting a graysby grouper, however, the worse its health. This burdens the graysby and may give lionfish an advantage in the competition for food and space.
The researchers also studied how lionfish parasitism varies regionally. They compared the variety and abundance of parasites in lionfish from four regions of their introduced range: Florida, Mexico, Belize, and Panama. They found certain parasites were more common at certain latitudes. At lower latitudes, like Panama, lionfish were infected with a greater variety and number of ectoparasites, parasites that live outside of their hosts.
These findings suggest that native parasites aren’t something we can count on to slow or stop the lionfish invasion. Rather, these parasites handicap the native fish, which right now are the invaders’ only competition in the Atlantic.
