For years, the runaway success of red lionfish in the Caribbean Basin has produced much debate among biologists, but a new study published in PLoS One may have isolated one powerful advantage of the invasive species. Authors Oona Lönnstedt and Mark McCormick of Australia’s James Cook University believe that lionfish might be “invisible” to their prey.

“Lionfish are native to the Pacific, but have been taking over the Caribbean Basin ever since they were accidentally introduced almost 30 years ago,” McCormick told phys.org. “Their extreme success as an invasive predator has long been a mystery to ecologists worldwide.”

In the study, researchers took a number of juvenile damselfish and exposed them to three predator species. The damselfish were able to detect rockcod and Zebra turkeyfish, but the red lionfish were virtually undetected.

“Surprisingly, the common prey fish were unable to learn that the lionfish represented a threat, which was very different to their response to two other fish predators,” Lönnstedt said.

The lionfish managed to sneak up on every single damselfish put in their tank, a success rate that was not matched by the other two predators. When researchers turned to the use of damselfish experienced with predators, they found that fewer fish were caught by rockcod and Zebra turkeyfish, but it did not dampen the red lionfish’s success rate. It seemed to be that because the invasive lionfish were so visually different from native predators in the Caribbean Basin, prey fish often failed to recognize them as a threat. Their natural camouflage and lack of odor makes lionfish an impressive marine predator.

“Our findings suggest that lionfish are one of the definitive fish predators,” researchers wrote in the study. “Their feeding success is not achieved though speed and surprise, but through a unique form of crypsis that circumvents the well-established mechanism whereby prey fishes learn about their predators.”

The researchers stated that few cases of invasive predators have been more devastating to the United State’s East Coast and the Caribbean Basin than lionfish, calling the species an “ultimate predator.” Many biologists and conservationists would agree. Lionfish are veritable swimming arsenals. Spiny, venomous fin rays deter predators and have long been the bane of divers across their natural range. Lionfish venom has been documented to cause convulsions, dizziness, nausea, and in extreme cases even paralysis and heart failure in humans. When hunting, lionfish will blow jets of water at prey animals to disorient them and are characterized as “aggressive” in their depredation of smaller fish.

Of the many species of lionfish, only the red and common lionfish have established populations in the Atlantic Ocean and are deemed invasive. The species was accidentally introduced to Florida in the mid-1980s, reputedly because aquarium owners wanted to dispose of a few unwanted specimens, and quickly took hold across the region. Lionfish are native to the Pacific Ocean, where they are kept in check by a few, specialized predators. In the Atlantic, their only predator is often a larger lionfish.

According to the study, these “hyper-successful nuisance invaders” have already impacted the populations of native fish and the marine environments they inhabit.

“It is only by obtaining a detailed understanding of the encounter between the lionfish predator and its native prey that we can better understand why these predators may have become so successful in their novel system,” Lönnstedt and McCormick wrote.

According to the National Oceanic and Atmospheric Administration, the only significant form of population control for invasive lionfish are human anglers and conservation efforts.

Image from Alexander Vasenin on the Wikimedia Commons

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  • Bart Smith

    “…only the red and common lionfish have established populations in the Atlantic Ocean and are deemed invasive.”

    Hmmm, my sources indicate that the red lionfish and the common lionfish are the same species, more “officially” known as the volitan lionfish.

    The ledges and wrecks off NC towards the deeper limits of SCUBA are absolutely infested with them. Mostly volitans, but I have also seen spotfin lionfish. The populations of native fish have been devastated in these areas.

    • mogul264

      Perhaps divers should start an extermination of these to ‘thin the herd’! Introducing another non-native predator to feed on lionfish can bring up a whole new set of problems! Just killing them will result a reduction in predators, especially the reds! Open season or whatever is necessary! The remains will be quickly extracted and eaten by other scavengers, crabs, etc.

      • Bart Smith

        We try, but there’s so dang many of them it would take an army of divers, working around the clock, months to even make a dent in the population.

        Plus, they reproduce ridiculously fast. I forget the exact numbers, but according to what I’ve read, a female can lay thousands upon thousands of eggs every few days. And it only takes about a year for one to reach sexual maturity. Reportedly the entire Atlantic population has been traced through DNA back to a half dozen females.

        They’re pretty tasty, but I’m not sure the risk of imposed by those spines when you have to get them off a spear and into a bag is worth it.

      • mogul264

        Rather that spearing, how about one of those ‘vacuum’ dredge hose things used in seabed gold collecting! Suck them up and run through a wire screen! Just chunks then! If they’re that thick, this would work wicked fast! AND, no dangerous fins to hazard removal from your spears! This would also work for those guys on “Sharks” to harvest them!

      • Bart Smith

        I’m not sure they’d stay still for you to get a dredge nozzle close enough to them to suck them in. Besides that, we’re talking about fairly deep water. The highest concentrations I’ve seen are on ledges in 250’+ range. Having to pull that much dredge hose through the water would make it dang near impossible to move across the bottom. Throw in the slightest amount of current and you’re going wherever it drags you.

        To just kill them, a spear with the barb removed works fine. You stick it through them and the water resistance makes them slide right off when you pull back – no real close contact.

        Like you said, a dredge would tear them to shreds and I was referencing trying to harvest them for food. In that case you’d need to get them in a bag or something and carry them back to the boat. This involves much closer contact, making the chance for one of those poisonous spines to stick you much greater.

        I’ve handled enough other fish to know that getting stuck by a spine is quite common, even when you’re being careful. It hurts and can get infected if you don’t take care of it, but with most fish it’s not a big deal. With a lionfish on the other hand…

      • mogul264

        Sorry, didn’t realize about the depth! That much hose, even a LIGHTER hose, would be MURDER to handle. Forget I said anything!

  • John1943

    There were a couple of guys on “sharks” the other day trying to raise money for a Lionfish harvesting scheme to sell these as table fish. I think it fell down because the team could not envisage large scale spearing being effective or adequate to supply sufficient fish.

    • Bart Smith

      The “Sharks” were correct. When commercial spear fishing you have to go for big, valuable fish to make it worthwhile. Unless your in real shallow water, you don’t have time to shoot, remove the fish from the spear, get him on a stringer or in a bag, and move onto the next fish very many times. Being that active, along with diving deep, makes you burn through your air supply in a hurry.

      Even with an infinite air supply, you still have to deal with no decompression time limits which get shorter with each successive dive. In the waters I dive, running up deco time and hanging out in the mid-water while holding a bag of dead, bleeding fish isn’t exactly the brightest idea. Sometimes, it’s sketchy enough when you can go straight from the bottom to the boat. So yeah, let’s dangle on a rope for an extended time period while holding a bag that puts out a scent trail for the tigers, bulls, and whoever else is in the neighborhood.