Pez león, un temible invasor
Fordivers blog

Lionfish, a fearsome invader

by Jorge Mezcua on Feb 21, 2023

Lionfish is the common name given to 10 species of venomous fish in the genus Pterois. These fish have become notorious for their destructive invasion of the Caribbean Sea and North America.

Lionfish are easily recognized by their pattern of dark vertical stripes ranging from brown to black mixed with lighter or white stripes. But what is more striking about this fish than its coloration are its fins, both anal and caudal, pectoral and dorsal, which are very long and covered with venomous spines. Undoubtedly, this animal cannot be called a traitor, since it constantly warns of its poison and danger. They are medium-sized fish, from 6 centimeters of the smallest of the genus to 42 cm. But the ones we usually associate with the image of the lionfish, the species Pterois Volitans, measure about 38 cm and can weigh up to 480 grams.

The lionfish is native to the coral reefs of the Asia-Pacific region, the countries around the Coral Triangle, the Indian Ocean to the Red Sea, and inhabits depths ranging from 4 to 120 meters.


Lionfish in Ras Mohammed, Red Sea. Image by albert kok

The poison of the lionfish

Lionfish are venomous animals that use the toxins in the spines of their fins (mainly in the dorsal fin) as a method of defense against predators. When they feel threatened, they show their dorsal fin (which has 18 venomous spines) to their attacker in an attempt to deter them. The effects of its venom, which is released when the spines are pressed and the amount released is proportional to the pressure received, like other venomous fish such as the stonefish, makes it more likely that it will not be swallowed by predators. 

Its venom is not fatal to humans, except for those who are allergic to its toxins, but the bite is very painful and causes nausea, fever and even vomiting. The treatment for a lionfish sting is first of all to stop swimming or bathing, wash the affected area with hot water up to 30ºC and go to the emergency room where they will remove the remains of the sting and apply specific treatment.

lionfish in the red sea

Lionfish in the Caribbean, pic by WIlly Volk

An invasion of difficult solution 

Exactly how lionfish made their way into the western Atlantic to occupy the Caribbean and much of the U.S. East Coast remains unclear. There are several theories regarding the beginning of the invasion, and it is believed to have begun in the early 1990s when Hurricane Andrew destroyed a South Florida aquarium and released six lionfish into Biscayne Bay.

Other sources suggest that lionfish were discovered around Florida as early as 1985, possibly because aquarium hobbyists dumped several lionfish into the ocean. In the last 20 years, lionfish have expanded their range from Cape Hatteras (North Carolina, United States) to Colombia, occupying the entire Caribbean.

In their natural habitat in the Indian and Pacific Oceans, lionfish have natural predators such as large moray eels, triggerfish, toadfish, sharks, groupers, drumlins and various species of scorpionfish that prey on them as just another reef dweller.

But in the Atlantic and the Caribbean, the native fish prefer to continue eating the species they have always eaten, rather than this new creature with a fearsome appearance, which some of them, after a first experience, would certainly prefer not to try again. Although there are already sharks or large groupers that eat them, the Atlantic and Caribbean have prey that is much more appetizing and easier to hunt.

Causes of lionfish plague

This lack of natural predators is one of the main reasons why lionfish have become a dangerous plague so quickly. To try and alleviate this serious problem, several experts in Roatan, Honduras are teaching sharks to eat lionfish by showing them that it is just another food source, as we mentioned earlier in this post. And you can already find videos of other species, such as large groupers or moray eels, feeding on them, but unfortunately it is not common.

Another reason why lionfish have become a pest is due to their nature, as they are very voracious predators, feeding on small fish and fry of potential predators such as groupers, among others. Lionfish also reproduce throughout the year, grow very fast, live up to 15 years and are fast and skilled hunters capable of devouring all types of prey.

This ability of these fish to survive and thrive has caused the lionfish population in some areas of the Caribbean to increase by as much as 700% in just 4 years, mainly of the Pterois Volitans species.

Fighting a relentless plague

For years, many local and international organizations have been trying to stop a plague that is causing serious ecological and economic damage to areas that depend on the ocean and on which many people depend.

These efforts have gone so far that in more than one marine protected area in Florida, and as of 2010, divers are allowed to kill as many lionfish as they can on each dive. Licenses also exist in parks in Cozumel and Honduras, where some divers have killed as many as 8 lionfish per dive.

Another type of activity carried out to alleviate this plague is the development of campaigns for the consumption of lionfish to promote the commercial fishing of this species, with the publication of cookbooks and specific recipes for the preparation of dishes with lionfish, or divers are asked to report, each time they make a dive, the areas, dive sites and number of lionfish found, in order to try to direct the efforts in the fishing of these fish.

Effects of the lionfish plague

The harmful effects of the lionfish plague, after almost 20 years in a territory not their own, are already being seen and may be even more damaging in the future, and many studies show that the food chain is being damaged.

On the one hand, the territorial nature of lionfish causes some native species to abandon their feeding and breeding grounds, reducing their populations and those of other species that used to feed on them. On the other hand, the gradual loss of different fish species in the Caribbean is seriously damaging the balance of the ecosystem. For example, among the species found in the stomachs of the lionfish studied were the royal grandmother fish (Gramma Loreto) or Apogon aurolineatus and several species of maidens or parrot fish such as Scarus iseri, all of which feed on algae, and the absence of this type of fish favors the uncontrolled growth of algae, seriously damaging the corals by preventing the entry of light into the reefs.

Other species preyed upon by the lionfish include the juvenile Haemulon plumierii, known as corocoro, chac-chí, ronco arará or ronco margariteño, which has a large presence in local markets and is the livelihood of many fishermen, and the Caribbean lobster, Panulirus argus, which the lionfish eats in its juvenile stage, seriously damaging the population of this lobster, the main food export of the Bahamas.

Several studies have already estimated that the loss of biodiversity in some areas due to the presence of lionfish is as high as 80%, an effect that is likely to have an impact on the dive tourism industry, as many divers will choose other destinations due to low biodiversity, few corals and too many lionfish.

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