Pterois is a genus of venomous marine fish, commonly known as lionfish, native to the Indo-Pacific. Pterois, also called zebrafish, firefish, turkeyfish or butterfly-cod, 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 a recent and significant invasive species in the west Atlantic, Caribbean Sea and Mediterranean Sea.
There are currently 12 recognized species in this genus:
- Pterois andover G. R. Allen & Erdmann, 2008 (Andover lionfish)
- Pterois antennata (Bloch, 1787) (Spot-fin lionfish)
- Pterois brevipectoralis (Mandritsa, 2002)
- Pterois cincta Rüppell, 1838 (Red Sea lionfish) 
- Pterois lunulata Temminck & Schlegel, 1843 (Luna lionfish)
- Pterois miles (J. W. Bennett, 1828) (Devil firefish)
- Pterois mombasae (J. L. B. Smith, 1957) (Frill-fin turkeyfish)
- Pterois paucispinula Matsunuma & Motomura, 2014 
- Pterois radiata G. Cuvier, 1829 (Clear-fin lionfish) 
- Pterois russelii E. T. Bennett, 1831 (Soldier lionfish)
- Pterois sphex D. S. Jordan & Evermann, 1903 (Hawaiian turkeyfish)
- Pterois volitans (Linnaeus, 1758) (Red 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 a day suggests lionfish feed most actively from 7:00–11:00 a.m., and decrease 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. In addition to confusing prey, these jets of water also alter the orientation of the prey so that the smaller fish is facing the lionfish. This results in a higher degree to predatory efficiency as head-first capture is easier for the lionfish. (In general, when smaller fishes escape from possible danger, they do so against the current.)
Predators and parasites
Aside from instances of larger lionfish individuals engaging in cannibalism on smaller individuals, adult lionfish have few identified natural predators, likely from 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.
Interaction with 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 venomous 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 adults, 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. There is a possibility for a human to be stung without any venom being injected. If venom is injected, the sting will hurt more than just briefly. Lionfish are not aggressive towards swimmers. Most accidents happen to fishermen, who happen to catch them.
Lionfish are edible if prepared correctly (see below).
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 twelve 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. They have been described as "one of the most aggressively invasive species on the planet".
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, before Hurricane Andrew. The lionfish resemble those of the Philippines, implicating the aquarium trade. The lionfish may have been purposely discarded by unsatisfied aquarium enthusiasts. This is in part because lionfish require an experienced aquarist, but are often sold to novices who find their care too difficult. In 2001, NOAA documented several sightings of lionfish off the coast of Florida, Georgia, South Carolina, North Carolina, Bermuda, and Delaware. In August 2014, when the Gulf Stream was discharging into the mouth of the Delaware Bay, two lionfish were caught by a surf fisherman off the ocean side shore of Cape Henlopen State Park: one red one that weighed 1 pound 4.5 ounces and one common one that weighed 1 pound 2 ounces. Three days later a 1-pound 3 ounce red lionfish was caught off the shore of Broadkill Beach which is in the Delaware Bay approximately 15 miles north of Cape Henlopen State Park. Lionfish were first detected in the Bahamas in 2004. In June 2013 lionfish were discovered as far east as Barbados, and as far south as the Los Roques Archipelago and many Venezuelan continental beaches. Lionfish were first sighted in Brazilian waters in late 2014. Genetic testing on a single captured individual revealed that it was related to the populations found in the Caribbean, suggesting larval dispersal rather than an additional release.
P. volitans and P. 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, Trinidad and Tobago, 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.
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.
The lionfish invasion is considered to be one of the most serious recent threats to Caribbean and Florida coral reef ecosystems. To help address the pervasive problem, in 2015 National Oceanic and Atmospheric Administration (NOAA) partnered with the Gulf and Caribbean Fisheries Institute to set up a lionfish portal to provide scientifically accurate information on the invasion and its impacts. The lionfish web portal is aimed at all those involved and affected, including coastal managers, educators and the public and the portal was designed as a source of training videos, fact sheets, examples of management plans, and guidelines for monitoring. The web portal draws on the expertise of NOAA's own scientists as well as other scientists and policy makers from academia NGO and managers.
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%.
Control and eradication efforts
Red lionfish are an invasive species, yet relatively little is known about them. NOAA has research foci 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.
Rigorous and repeated removal of lionfish from invaded waters could potentially control the exponential expansion of the lionfish in invaded waters. A 2010 study showed effective maintenance would require the monthly harvest of at least 27% of the adult population. Because lionfish are able to reproduce monthly, this effort must be maintained throughout the entire year.
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, for the first time the Florida Keys National Marine Sanctuary began licensing divers to kill lionfish inside the sanctuary in an attempt to eradicate the fish.
Conservation groups and community organizations in the Eastern United States have organized hunting expeditions for Pterois such as the Environment Education Foundation's ‘lionfish derby’ held annually in Florida. Divemasters from Cozumel to the Honduran Bay Islands and at Reef Conservation International which operates in the Sapodilla Cayes Marine Reserve off Punta Gorda, Belize, now routinely spear them during dives.
While culling by marine protection agencies and volunteer divers is an important element of control efforts, development of market-based approaches, which create commercial incentives for removals, has been seen as a means to sustain control efforts. The foremost of these market approaches is the promotion of lionfish as a food item. Another is the use of lionfish spines, fins and tails for jewelry and other decorative items. Lionfish jewelry production initiatives are underway in Belize, the Bahamas and St. Vincent and the Grenadines.
Lionfish as Food campaign
In 2010, NOAA began a campaign to encourage the consumption of the fish. The "Lionfish as Food" campaign encourages human hunting of the fish as the only form of control known to date. Encouraging the consumption of lionfish could not only help to maintain a reasonable population density, but also provide an alternative fishing source to overfished populations, such as grouper and snapper. NOAA also encourages people to report lionfish sightings, to help track lionfish population dispersal. To promote the campaign, the Roman Catholic Church in Colombia agreed to have their clergy's sermons suggest to their parishioners (84% of the population) to eat the fish species on Fridays, Lent and Easter, which proved highly successful to decrease the invasive fish problem.
When properly filleted, the naturally venomous fish is safe to eat. There has been some concern about the risk of ciguatera food poisoning (CFP) from consumption of lionfish, and the FDA included lionfish on the list of species at risk for CFP when lionfish are harvested in some areas tested positive for ciguatera. However, there have been no verified cases of CFP from consumption of lionfish, and published research has found that the toxins in lionfish venom may be causing false positives in tests for presence of ciguatera. The Reef Environmental Education Foundation provides advice to 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. Recipes for lionfish include deep frying, ceviche, jerky, grilling,and sashimi.
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