Pterois is a genus of venomous marine fish, commonly known as lionfish, native to the Indo-Pacific. Pterois is characterized by conspicuous warning coloration with red, white, creamy, or black bands, showy pectoral fins, and venomous spiky fin rays. Pterois radiata, Pterois volitans, and Pterois miles are the most commonly studied species in the genus. Pterois species are popular aquarium fish. P. volitans and P. miles are significant invasive species in the west Atlantic and Caribbean Sea.
The currently recognized species in this genus are:
- Pterois andover G. R. Allen & Erdmann, 2008
- Pterois antennata (Bloch, 1787) (spotfin lionfish)
- Pterois brevipectoralis (Mandritsa, 2002)
- Pterois lunulata Temminck & Schlegel, 1843 (luna lionfish)
- Pterois miles (John Whitchurch Bennett, 1828) (devil firefish)
- Pterois mombasae (J. L. B. Smith, 1957) (frillfin turkeyfish)
- Pterois radiata G. Cuvier, 1829 (clearfin lionfish)
- Pterois russelii E. T. Bennett, 1831 (soldier lionfish)
- Pterois sphex D. S. Jordan & Evermann, 1903 (Hawaiian turkeyfish)
- Pterois volitans (Linnaeus, 1758) (red lionfish, volitans lionfish)
Pterois fish in the Atlantic range from 5 to 45 cm (2.0 to 17.7 in) in length, weighing from 0.025 to 1.3 kg (0.055 to 2.866 lb). They are well known for their ornate beauty, venomous spines, and unique tentacles. Juvenile lionfish have a unique tentacle located above their eye sockets that varies in phenotype between species. The evolution of this tentacle is suggested to serve to continually attract new prey; studies also suggest it plays a role in sexual selection.
Ecology and behavior
Pterois species can live from five to 15 years and have complex courtship and mating behaviors. Females release two mucus-filled egg clusters frequently, which can contain as many as 15,000 eggs. Studies on Pterois reproductive habits have increased significantly in the past decade. All the species are aposematic: they have conspicuous coloration with boldly contrasting stripes and wide fans of projecting spines, advertising their ability to defend themselves.
According to a study that involved the dissection of over 1,400 lionfish stomachs from Bahamian to North Carolinian waters, Pterois fish prey mostly on small fish, invertebrates, and mollusks in large amounts, with some specimens’ stomachs containing up to six different species of prey. The amount of prey in lionfish stomachs over the course of the day suggests lionfish feed most actively from 7:00–11:00 am, with decreased feeding throughout the afternoon. Lionfish are skilled hunters, using specialized bilateral swim bladder muscles to provide exquisite control of location in the water column, allowing the fish to alter its center of gravity to better attack prey. The lionfish then spreads its large pectoral fins and swallows its prey in a single motion. They blow jets of water while approaching prey, apparently to disorient them.
Predators and parasites
Aside from instances of larger lionfish individuals engaging in cannibalism on smaller individuals, adult lionfish have few identified natural predators. This is likely due to the effectiveness of their venomous spines. Moray eels (family Muraenidae), bluespotted cornetfish (Fistularia commersonii), and large groupers, like the tiger grouper (Mycteroperca tigris) and Nassau grouper (Epinephelus striatus), have been observed preying on lionfish. It remains unknown, however, how commonly these predators prey on lionfish. Sharks are also believed to be capable of preying on lionfish with no ill effects from their spines. Park officials of the Roatan Marine Park in Honduras have attempted to train sharks to feed on lionfish as of 2011 in an attempt to control the invasive populations in the Caribbean. Predators of larvae and juvenile lionfish remain unknown, but may prove to be the primary limiting factor of lionfish populations in their native range.
Hazard to humans
Lionfish are known for their venomous fin rays, an uncommon feature among marine fish in the East Coast coral reefs. The potency of their venom makes them excellent predators and poisonous to fishermen and divers. Pterois venom produced negative inotropic and chronotropic effects when tested in both frog and clam hearts and has a depressing effect on rabbit blood pressure. These results are thought to be due to nitric oxide release. In humans, Pterois venom can cause systemic effects such as extreme pain, nausea, vomiting, fever, breathing difficulties, convulsions, dizziness, redness on the affected area, headache, numbness, paresthesia (pins and needles), heartburn, diarrhea, and sweating. Rarely, such stings can cause temporary paralysis of the limbs, heart failure, and even death. Fatalities are common in very young children, the elderly, those with a weak immune system, or those who are allergic to their venom. Their venom is rarely fatal to healthy humans, but some species have enough venom to produce extreme discomfort for a period of several days. However, Pterois venom is a danger to allergic victims as they may experience anaphylaxis, a serious and often life-threatening condition that requires immediate emergency medical treatment. Severe allergic reactions to Pterois venom include chest pain, severe breathing difficulties, a drop in blood pressure, swelling of the tongue, sweating, runny nose, or slurred speech. Such reactions can be fatal if not treated.
Lionfish are edible if prepared correctly.
Native range and habitat
The lionfish is a predator native to the Indo-Pacific. It aggressively preys on small fish and invertebrates. They can be found around the seaward edge of reefs and coral, in lagoons, and on rocky surfaces to 50 m deep. They show a preference for turbid inshore areas and in harbors, and have a generally hostile attitude and are territorial towards other reef fish. Many universities in the Indo-Pacific have documented reports of Pterois aggression towards divers and researchers.
Invasive introduction and range
Two of the nine species of Pterois, the red lionfish (P. volitans) and the common lionfish (P. miles), have established themselves as significant invasive species off the East Coast of the United States and in the Caribbean. About 93% of the invasive population in the Western Atlantic is P. volitans.
The red lionfish is found off the East Coast of the United States and the Caribbean Sea, and was likely first introduced off the Florida coast by the early to mid-1990s. This introduction may have occurred in 1992 when Hurricane Andrew destroyed an aquarium in southern Florida, releasing six lionfish into Biscayne Bay. However, a lionfish was discovered off the coast of Dania Beach, south Florida, as early as 1985, prior to Hurricane Andrew. The lionfish resemble those of the Philippines, implicating the aquarium trade. The lionfish may have been purposefully discarded by unsatisfied aquarium enthusiasts. In 2001, NOAA documented multiple sightings of lionfish off the coast of Florida, Georgia, South Carolina, North Carolina, and Bermuda, and they were first detected in the Bahamas in 2004. Recently (June 2013) they have been discovered as far east as Barbados, and as far south as the Los Roques Archipelago and many Venezuelan continental beaches.
P. volitans and P.terois miles are native to subtropical and tropical regions from southern Japan and southern Korea to the east coast of Australia, Indonesia, Micronesia, French Polynesia, and the South Pacific Ocean. Adult lionfish specimens are now found along the United States East Coast from Cape Hatteras, North Carolina, to Florida, and off Bermuda, the Bahamas, and throughout the Caribbean, including the Turks and Caicos, Haiti, Cuba, the Dominican Republic, the Cayman Islands, Aruba, Curacao, Bonaire, Puerto Rico, St. Croix, Belize, Honduras, and Mexico. Population densities continue to increase in the invaded areas, resulting in a population boom of up to 700% in some areas between 2004 and 2008. Population densities have reached levels orders of magnitude greater than in their native ranges.
Pelagic larval dispersion is assumed to occur through oceanic currents, including the Gulf Stream and the Caribbean Current. Currents could eventually result in new populations along the Gulf Coast. Ballast water can also contribute to the dispersal.
Extreme temperatures present geographical constraints in the distribution of aquatic species, indicating temperature tolerance plays a role in the lionfish’s survival, reproduction, and range of distribution. The abrupt differences in water temperatures north and south of Cape Hatteras directly correlate with the abundance and distribution of Pterois. Pterois expanded along the southeastern coast of the United States and occupied thermal-appropriate zones within 10 years. Although the timeline of observations points to the east coast of Florida as the initial source of the western Atlantic invasion, the relationship of the United States East Coast and Bahamian lionfish invasion is uncertain. Lionfish can tolerate a minimum salinity of 5 parts per thousand and even withstand pulses of freshwater, which means they can also be found in estuaries of freshwater rivers.
Control and eradication efforts
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The population density of the invasive lionfish is increasing very quickly, and efforts are underway in several areas to bring it under control. However, to completely eradicate the lionfish from its new habitats seems unlikely. A study from 2010 using population modeling used data collected about the known life history of the lionfish inhabiting the Caribbean coral reefs to figure out the best means of eradication. The study showed the most effective way to even maintain current lionfish population densities, at least 27% of the invasive adult populations would have to be killed monthly. Because lionfish are able to reproduce monthly throughout the entire year, this effort must be maintained monthly for the maintenance of current population densities.
Even to accomplish these numbers seems unlikely, but as populations of lionfish continue to grow throughout the Caribbean and Western Atlantic, actions are being taken to attempt to control the quickly growing numbers. In November 2010, the Florida Keys National Marine Sanctuary began to give out licenses to divers to kill lionfish inside of the sanctuary. This is the first time this has ever been done for any species in the sanctuary, in a desperate attempt to eradicate the fish. Rigorous and repeated removal of lionfish from invaded waters will be necessary to establish control on the exponentially expanding population. Many conservation groups across the Eastern United States are organizing hunting expeditions for Pterois. The Environment Education Foundation recently hosted its third ‘lionfish derby’ in Florida, offering more than $3,000 in prize money for dive teams catching the most lionfish. Community organizations are forming across the country in hopes of halting the ever-expanding lionfish population. Divemasters from Cozumel to the Honduran Bay Islands routinely spear them during dives, sometimes killing as many as eight in an hour. Divers at Reef Conservation International's headquarters off Punta Gorda, Belize, spear an average of 30 lionfish per dive, with the single diver maximum record being 54 on one dive. Based on average kills per dive, a professional diver could easily kill 3000 to 4000 lionfish per year (three dives per day, six days per week, averaging four or more kills per dive).
Other interest groups, such as NOAA, are setting up events and campaigns to encourage the killing and eating of the fish. Many people are wary of the idea of eating a venomous fish, but when properly filleted, the fish is safe to eat. Encouraging the consumption of lionfish could not only help to maintain a reasonable population density, but also provide an alternative fishing source to other overfished populations, such as grouper and snapper. The Reef Environmental Education Foundation has even prepared a cookbook to help educate restaurant chefs on how they can incorporate the fish into their menus. The NOAA calls the lionfish a "delicious, delicately flavored fish" similar in texture to grouper. Many recipes for lionfish can be found in coastal cookbooks, some including fried lionfish, lionfish ceviche, lionfish jerky, and grilled lionfish.
The invasiveness of the red lionfish is an extreme problem, and relatively little information is still known about the animal. The NOAA has research foci in place to better understand the fish and the implications surround its invasive nature. Some of these include investigating biotechnical solutions for control of the population, and understanding how the larvae are dispersed. Another important area of study is what controls the population in its native area. Researchers hope to discover what moderates lionfish populations in the Indo-Pacific and apply this information to control the invasive populations, without introducing additional invasive species. NOAA also plans to further its "Lionfish as Food" campaign, since human hunting of the fish is the only form of control known as of September 2013. The NOAA also encourages people to report lionfish sightings, to help track lionfish population dispersal.
Long-term effects of invasion
Lionfish have successfully pioneered the coastal waters of the Atlantic in less than a decade and pose a major threat to reef ecological systems in these areas. A study comparing their abundance from Florida to North Carolina with several species of groupers found they were second only to the native scamp grouper and equally abundant to the graysby, gag, and rock hind. This could be due to a surplus of resource availability resulting from the overfishing of lionfish predators like grouper. Although the lionfish has not expanded to a population size currently causing major ecological problems, their invasion in the United States coastal waters could lead to serious problems in the future. One likely ecological impact caused by Pterois could be their impact on prey population numbers by directly affecting food web relationships. This could ultimately lead to reef deterioration and could negatively influence Atlantic trophic cascade. Lionfish have already been shown to overpopulate reef areas and display aggressive tendencies, forcing native species to move to waters where conditions might be less than desirable.
Lionfish could be decreasing Atlantic reef diversity by up to 80%. In July 2011, lionfish were reported for the first time in the Flower Garden Banks National Marine Sanctuary off the coast of Louisiana. Sanctuary officials said they believe the species will be a permanent fixture, but hope to monitor and possibly limit their presence.
Since lionfish thrive so well in the Atlantic and the Caribbean due to nutrient-rich waters and lack of predators, the species has spread tremendously. A single lionfish, located on a reef, reduced young juvenile reef fish populations by 79%. 
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