The lionfish is an Olympic athlete of digestion — and that's an ecological disaster

Originally published on November 9, 2019.

The lionfish is known to be a ferocious predator. Now scientists have discovered just how ferocious a digester the invasive species can be.

Lionfish have delicate, ornamental fins that fan out around their bodies, resembling a lion's mane. They are native to waters off Fiji, and were probably accidentally released in the Atlantic Ocean in the 1980s. Since then, the population has exploded around the Caribbean and in waters off the southeastern U.S.

Canadian Erika Eliason, an assistant professor of ecology, evolution and marine biology at the University of California, Santa Barbara, was part of a team that studied how the lionfish's appetite could contribute to its success as an invasive predator.

Eliason and colleagues from Carleton University used nets while scuba diving to capture lionfish in the Bahamas, taking care to avoid the creature's venomous spines. 

Then they took the lionfish to tanks in the lab. Next they fed the fish as many silverside prey as they could gobble. 

The researchers also used a respirometer — a device that measures oxygen consumption, to get a picture of the animals level of metabolic activity.

They found the lionfish were capable of eating huge meals — up to 13 per cent of their body mass. But what was really remarkable was the amount of metabolic energy they were able to devote to digestion, the team reported in October in the Journal of Experimental Biology. 

The scientists chased the fish around a tank to try to max out the animals' metabolic rate.  They found that their metabolism was operating at a much higher level — about 1.7 times higher — when they were eating, than when they were swimming vigorously. They say this is quite different from other predatory fish.

"They seem to just be able to stuff themselves completely and use up all their energetic capacity for digestion without leaving any energy in the tank for locomotion. It's kind of like if you eat a whole bunch of food during Thanksgiving and just lay on the couch and can't move at all. It's like lionfish, that's their strategy."

A tasty solution

Eliason suspects the venomous spines on the lionfish's fins mean it doesn't need to escape from predators. Instead, lionfish can devote their energy to pigging out and digesting the meal. 

What's more, the researchers found lionfish ate more and digested more efficiently at a warm temperature.

The concern is, that efficiency might translate into a more invasive predator that could also expand its range north. 

To keep its numbers in check, local campaigns encourage people to spear and eat lionfish. 

"I can say firsthand that lionfish are very tasty," Eliason said.