Lionfish

The case of the pretty, nasty fish

The lionfish is a type of bony marine fish native to the Indian and Pacific Oceans. It belongs to the scorpionfish family.

Pterois volitans is the scientific name given to the red lionfish and it is closely related to the devil lionfish (Pterois miles), so the use of lionfish in this context covers P. miles although most records used for research for this page are about P. volitans. Other names include peacock lionfish, red firefish, turkeyfish.

The Misplaced

Appearance

These fish have prominent elongated fins and spines which make them conspicuous. The membranes of the fins are often spotted. The body is white or cream coloured with red to reddish-brown vertical stripes of variable widths. Venom glands at the base of certain fin spines produce a number of toxins (collectively “venom”) that are injected in a potential predator via the spines. The venom of the red lionfish may be delivered by spines of the dorsal, anal and pelvic fins and is known to cause a severe reaction in humans.

They grow to a length of about 40 cm and average weight is around 1.2 kg.

Ecology and feeding

The preferred habitats 0f P. volitans are areas of warm water with coral reefs or coastal waters with rocky bottoms to lurk in. They also appear to like artificial reefs and sunken ships. Lionfish cannot breed in waters colder than 10 degrees Celsius, so this limits their distribution to tropical and temperate regions. Typically lionfish inhabit depths down to about 50 meters, but there are reports of sightings down to 300m.

A lionfish's diet consists primarily of fish and crustaceans. They hunt mostly at night, and have two major hunting strategies
1) they use their long fins to corral a prey animal into a corner and gobble them up whole
2) they stalk a prey animal and then strike at it extremely quickly and gobble it up whole

Voracious, unfussy feeders, they will eat any suitable prey that they can fit into their mouths. And they can expand their stomachs to accommodate large amounts of food if the opportunity comes their way. On the other hand, they can survive without food for weeks at a time when food is scarce.

Predators known to hunt lionfish in their native habitat include cornetfish, grouper, large eels, bobbit worms, frog fish, other scorpionfish, sharks and others. In areas they have invaded, they do not suffer from heavy predation as many of the potential hunters have not had time to recognise them as prey species.

Reproduction and Life cycle

Female lionfish are sexually mature at approx 12 months old.

Under optimal temperature conditions, lionfish readily mate at any time of the year. A female can lay up to 2 million eggs in a year. The eggs are fertilised externally, and begin to form embryos just twelve hours after fertilization. The eggs hatch into larvae in 36 hours. The larvae are then dispersed by ocean currents. Juveniles differ in form from adults, and it takes about 4 months for all adult features to be developed.

The average lifespan of P. volitans in the wild is approx. 10 years.

The Displaced

The presence of P. volitans and P. miles is probably due to deliberate or inadvertent releases from aquaria both (domestic and commercial), or from ballast water released from ships.
Lionfish do not target specific species when they invade. They outcompete native predators of fish, due to their voracious appetites and quick reproductive cycle. They can exert some pressure on the whole ecosystem by changing the balance of the food web. By preying on herbivorous fishes that consume macro-algae, P. volitans creates an increase in the likelihood of algal overgrowth which will exert a negative effect on the invaded environments.

The consequences

Where is the invasion?

Note: In addition to the well known invasion of the Atlantic Ocean, lionfish are using the Suez Canal to gain access to Mediterranean waters.

lionfish global distribution :drawing — lionfish global distribution

Mediterranean spread of lionfish sightings

Some facts about the consequences of lionfish invasion

Lionfish can reach densities of over 1 adult every 200 square meters.
On sites with heavy infestations, lionfish have been responsible for about 90% reductions in the populations of native fish they prey on.
Lionfish have minimal impact from parasites compared to native fish species.

Adapted from REEF factsheet

Case study: The Caribbean Sea

It only took lionfish 5 years to spread throughout the Caribbean Sea, where they are increasing coral reef ecosystem stress.

Animated version is available at Lionfish University

Case study: Brazilian coastal waters

Off the Brazil coast, sporadic records of low numbers of lionfish have been made since 2014. It was thought these were not indicative of established populations.

In 2022, a more systematic study was made. A team of 20 scientists released a journal article in which they reported on

the continuing invasion process along the Brazilian Province by multiple sightings (72) of lionfish from March to May 2022 in estuaries, seagrass beds, and artificial and natural reefs across 240 km of the Brazilian coast. These are the first records of lionfish in coastal northeast Brazil and the shallowest records (1–16 m) from South Atlantic tropical waters. The largest simultaneous records of lionfish in breakwaters, fishing weirs, and marambaias (artificial reefs used as fishing grounds) on the Brazilian Northeastern coast indicate that these man-made structures are suitable habitats for this species. Most of the lionfish (58%) were recorded in artificial reefs and fishing weirs. Moreover, the detection of invasions in marginal reefs, estuaries, and two marine protected areas characterized by moderately turbid water and high sedimentation rates highlights the adaptability of the lionfish, making it extremely difficult for divers and fishers to capture them.

The invasion success and establishment of lionfish are attributable to its dispersal mode, high reproductive rates, rapid growth, lack of natural predators in invaded areas, defensive venomous spines, cryptic habits, color and behavior, habitat generality, high competitive ability, low parasite load, and efficient predation. These biological and ecological attributes allowed the rapid geographic spread of this species in new environments, causing ecological impacts with multiple detrimental effects on native populations, threatening local biodiversity and some economically important species.¹

Tackling the lionfish problem

One strategy to reduce lionfish populations is conducting fishing tournaments which can rapidly lower lionfish numbers temporarily if well attended. Also, officials have tried offering bounties for catches. And there have been attempts to promote a retail industry in providing lionfish to restaurants as it is regarded as tasty eating.

Another tack is the use of specially designed lionfish traps, although these do not, as yet, have a high rate of success.

Some effort has been put into teaching sharks to hunt and eat lionfish. A problem with this appears to be the learning capacity of sharks. They will eat lionfish given to them but most have not connected this with catching them for themselves in the wild. It is thought that local grouper species are naturally learning to catch lionfish.

While total removal is proving very difficult, keeping numbers down through these strategies does take some of the pressure off natives.