With water constituting about 71% of the earth’s surface, most of the planet’s organisms inhabit water bodies. It’s safe to assume that the oceans and seas have a myriad of dangerous creatures since the land has a fair share of deadly animals.
Fishes are significant water-dwelling critters and the most numerous vertebrates on the planet. However, unlike the typical gentle and vulnerable fishes in artificial ponds and aquariums, natural water bodies serve as homes for various harmful fish species. While some are bloodthirsty predators, others are poisonous or possess other fatal defensive mechanisms.
This guide presents the world’s ten most dangerous fish. We highlight in detail the fish species that can harm humans to enable you to avoid them entirely or apply caution when dealing with them if you must. Also, it provides information on the treatment solutions for the venom of some dangerous fishes.
Before going into the main issue, it’s necessary to evaluate and appreciate the animal species referred to as “fish” briefly.
A Recap of the Makeup of Fishes
The term “fishes” refers to several species of vertebrates that inhabit the world’s fresh and salt waters. With about 36,000 species, fish constitutes the broadest vertebrate group. The species within the group show pretty much distinction as the other vertebrate classes differ from each other.
There are five classes of living fishes, with these being the three largest:
- Agnathans or jawless fishes have gills in pouches and lack limb girdles, e.g., lampreys and hagfishes.
- Chondrichthyes or cartilaginous fishes are made entirely of cartilage, lack a swim bladder, and their scales and teeth consist of placoid materials, e.g., sharks, rays, and skates.
- Bony fishes are the largest class. Its members possess scales made up of overlapping thin bone plates and operculum-covered gill slits, e.g., seahorses, blue marlins, puffers, and ocean sunfishes.
Generally, fishes share several features with other vertebrates, including:
- Gill slits, which other vertebrates possess at some point in their lifecycle
- A notochord or skeletal-supporting rod
- A posterior hollow nerve cord
- A tail
Although most fishes are cold-blooded, the opah (Lampris guttatus) is distinctly warm-blooded.
The animals termed “fishes” have existed for over 450 million years. They’ve evolved continuously to fit into most aquatic habitat types within this period.
Fun Fact — Land vertebrates are highly modified fishes. When some fish species colonized the terrestrial habitat, they evolved to become four-legged (tetrapod) vertebrates.
Several fishes conform to their typical definition as slippery, streamlined water-dwelling vertebrates. However, there are more distinctive species.
For instance, some possess elongated bodies, while others have shortened bodies. Their bodies may be flattened or laterally compressed, primarily in fishes that live at the bottom of water bodies.
Fish fins are another variable feature; some are highly extended, comprising complex shapes while others are reduced. On the contrary, some fish species lack fins entirely. In addition, the positions of the eyes, nostrils, mouths, and gill openings differ significantly.
The nutritional habits of fish depend on the species. Some species, such as sharks, mosquitofish, and piranhas, are carnivorous, feeding on other fishes, mosquito larvae, or other aquatic creatures. On the other hand, several fish species are herbivorous, consuming aquatic plants, algae, or lichens.
Most fishes hatch from somewhat small eggs within a few days to several weeks following the dispersal of the eggs into the water. Recently hatched young fishes, called larvae, are partially undeveloped. Eventually, their body structures, including fins, organs, and skeleton, become fully formed.
Most Dangerous Fish in the World
Fish are beneficial to humans as a food source, attractive pets, and mosquito-controlling creatures. Still, some species pose severe risks to humans. Several fish species may attack humans, while others deliver poison shots if they are mishandled or threatened.
The top ten most dangerous fishes include:
- Red lionfish
- Great white shark
- Moray eels
- Atlantic mantra
- Electric eel
Let’s take a good look at each species and what makes them particularly dangerous.
10. Puffers (Tetraodon lineatus)
Puffers refer to various fish species in the family Tetraodontidae. There are about 90 species in the family.
Recognized by numerous names, including swellfish, pufferfish, balloonfish, or blowfish, they’re primarily marine and estuarine species, living in the sea and brackish water. They may also inhabit freshwater in some cases.
Fun Fact — Puffers are also called balloonfish or swellfish because of their remarkable ability to immensely inflate themselves with air and water to become globular in shape when disturbed or threatened.
These species are found in both warm and temperate regions of the world. Typically, they have strong, prickly skins and four relatively large teeth merged into an upper and lower plate.
Their fused teeth, the basis of their scientific name (Tetraodontidae), form a beak-like structure with a split between each jaw. The giants of the species grow to approximately 90 centimeters (3 feet) long, but most are way tinier.
Pufferfishes are carnivorous, feeding on crustaceans and mollusks. Their modified teeth are an adaptive feature for crushing the hard shells of their prey.
Most pufferfishes are poisonous, and some are reputable among the most poisonous vertebrates on the planet. Several species’ internal organs, including the liver and occasionally the skin, contain tetrodotoxin, a highly toxic substance. When eaten, they’re lethal to most animals.
Regardless, the meat of various puffers is used as food, particularly in Japan, where it forms a delicacy known as fugu. The diet must be prepared by specially trained chefs who are aware of the safe parts of the fish and the adequate quantity to consume.
Meanwhile, the dish is entirely avoided by the royal family due to the extreme toxicity of various puffers. In Korea and China, puffer meat is used to prepare bogeo and hétún, respectively.
In Florida, the authorities have banned the harvesting of puffers from several water bodies due to the neurological symptoms exhibited by people who consume pufferfish in Titusville, Florida.
The treatment for pufferfish poisoning is primarily supportive. It employs gastric lavage and activated charcoal to decontaminate the intestines.
In addition, the patient requires life support until the toxin is metabolized. Several accounts indicate anticholinesterases, such as edrophonium, may be effective against tetrodotoxin.
9. Red lionfish (Pterois volitans)
Lionfishes, also known as Pterois, are various showy fish species native to the Indo-Pacific region. They belong to Scorpaenidae, the scorpionfish family, and the order Scorpaeniformes. Notable as a venomous coral reef fish, the red lionfish is presently an invasive species in the Caribbean sea and East Coast water bodies of the United States.
The red lionfish is among the most renowned species of Pterois, commonly kept by fish lovers. It possesses red, white, and brown stripes and measures about 30 centimeters (12 inches) as an adult. Apart from its prominent zebra-like stripes pattern, it has long dorsal fin spines and broadened pectoral fins.
Fun Fact — Like other lionfishes, the red lionfish has enormous venomous spines protruding from its body, reminiscent of a lion’s mane. Hence, the name “lionfish.”
The fish’s peculiar venomous dorsal spines make it inedible and help it to defend itself against potential predators. When facing a threat, the red lionfish spreads and displays its fins to warn the attacker and flips upside-down to sting the assailant with its spines if the threat persists.
Although the sting isn’t fatal to humans, envenomed humans experience several uncomfortable symptoms.
Symptoms of being stung by a lionfish may include:
- Severe pain
- Breathing difficulties
The treatment usually involves soaking the affected part in hot water as most hospitals don’t perform specific therapies.
The red lionfish has a quick reproduction rate. In conjunction with the absence of natural enemies in the East Coast and Gulf of Mexico regions, it has resulted in its establishment as an invasive species and significant reduction of local reef fishes.
Generally, lionfish are ravenous feeders, hunting from late afternoon to the next day, and have even outcompeted other predatory fish. They hunt by cornering their prey with their large fins and subsequently using their sharp reflexes to swallow the game wholly.
The increasing population of red lionfish and their high prey consumption rates may play a significant role in the currently waning fish densities trend. Thus, they are becoming a danger to delicate ecosystems due to their invasive nature.
8. Candiru (Vandellia cirrhosa)
The candiru, also known as vampire fish, is a scaleless, parasitic freshwater catfish belonging to the Trichomycteridae family. They’re native to the Amazon River area, including:
Candirus are translucent and resemble eels. Smaller species may grow to about 2.5 centimeters (1 inch).
Other common characteristics of candirus include:
- A small head surrounded by short sensory barrels
- Gill covers with backward-pointing spines
- An apparently distended belly
They feed on blood and are typically seen in the gill cavities of larger fishes. Although commonly thought to infiltrate the urethras of swimming animals, the idea of candirus entering human urethras is still controversial.
There have been several alleged cases of smaller candirus species invading and parasitizing the human urethra, with some reports dating back to the 19th century. However, the first documented surgical removal of a candiru from the human urethra didn’t occur until 1997, and the event is still debatable.
When candirus enters host animals’ passage, they erect the sharp spines on their gill covers, resulting in bleeding and hemorrhage, and possibly the victim’s death.
Quick Fact — It’s pretty challenging to detect these fish species in the turbid waters they inhabit due to their bodies’ transparency.
It would help if individuals were careful around untreated natural freshwater.
7. Great White Shark (Carcharodon carcharias)
Also referred to as the white shark or white pointer, the great white shark is among the world’s most powerful and possibly deadly predatory sharks. Thanks to Steven Spielberg’s 1975 movie Jaws, this creature needs no introduction. Although publicly feared and a popular subject of animal discussions, there’s not much known about the great white shark’s life and behavior.
They’re large mackerel shark species found on the nearshore surface of all the world’s major oceans.
Fun Fact — Sharks are regarded as the planet’s largest known macropredatory fish species. The females are larger, measuring up to 6.1 meters (20 feet) and weighing about 1,905–2,268 kilograms (4,200–5,000 pounds) at maturity.
With a 2014 BBC report suggesting that white sharks may live up to 70 years or more, they’re among the longest-lived cartilaginous fishes. The fossil record indicates modern white sharks have been around for nearly 12–18 million years since the mid-Miocene Epoch period. Still, their ancestors may have lived around the Eocene Epoch, approximately 56–34 million years ago.
Though humans aren’t white pointers’ choice of prey, these fish are responsible for most reported and observed incidents of deadly unprovoked shark attacks on humans. They attack swimmers, kayakers, surfers, divers, and little boats in regions where they’re most populated.
These attacks are relatively rare, usually less than 10 cases a year worldwide. In most cases, a great white shark tends to bite its human victim once and retreat, but occasionally the shark returns for another bite.
If the shark bite is moderate, the individual may have time to flee to safety. However, large bites may result in tissue and organ damage, ultimately leading to the victim’s death.
An evaluation of great white shark attacks on humans in the western United States indicated that approximately 7% of the assaults were fatal. However, other parts of the world recorded higher fatalities, with South Africa having fatality rates exceeding 20% and Australia’s casualty rates as high as 60%.
Numerous researchers opine that sharks attack humans due to their curiosity. On the contrary, other scholars argue that shark attacks result from the sharks mistaking humans for their natural prey, like seals and sea lions. Sharks may also attempt to attack humans when their usual game becomes scarce.
6. Moray Eels (Muraena)
Moray eels are a family of eels primarily found in marine waters worldwide. There are more than 80 extant species of moray eels. In tropical and subtropical seas, they occupy shallow waters among rocks and reefs and conceal themselves in ravines.
Generally, moray eels don’t grow longer than 1.5 meters (5 feet).
Their dorsal fin extends from behind their head across their back and seamlessly unites the caudal and anal fins. Most moray eel species lack pectoral and pelvic fins, contributing to their serpentine appearance. Having relatively small eyes, morays largely depend on their highly developed sense of smell to hunt prey.
Moray eels generally possess a patterned body and have thick and smooth skin that lacks scales. In several species, the internal aspect of the mouth is also patterned.
They also have broad jaws at the edges of their protruding snout. Within their jaws are large, hard, sharp teeth employed when tearing flesh or grasping slippery prey. They may also use their teeth to inflict severe injuries on their attackers, including humans.
Moray eels are inclined to attack humans only when threatened. In such a case, they become somewhat violent. The Pacific’s Thyrsoidea macrurus is an exception, growing to about 3.5 meters (11.5 feet).
Moray eels are eaten in several regions, notably in Ancient Rome, where Muraena helena was a well-loved delicacy. However, moray eels aren’t recommended for consumption due to their potential danger.
Various moray species, specifically the giant moray and yellow-edged moray, possess high levels of ciguatoxins. The toxins are most abundant in the liver.
The following symptoms characterize ciguatera (moray eel poisoning):
- Neurological problems
- Gastrointestinal disorders
- Cardiovascular issues
The term “tigerfishes” refers to several fish species.
They are primarily named on the following bases:
- Their aggressiveness when caught
- Their fiercely predatory habitats
- Their appearance
Many belong to the genus Hydrocynus (Hydrocyon) and inhabit African freshwaters. They belong to the Characin family (Characidae) in the order Cypriniformes.
Generally, they’re marked, a distinctive feature relying on the species. In addition, they have one or more dark, lengthwise stripes.
Tigerfishes are fast, desirous, salmon-shaped carnivores. They have dagger-like teeth that protrude when their mouth is closed.
There are about five species of African tigerfishes, with the largest, Hydrocynus goliath, exceeding 1.8 meters (6 feet) and weighing over 57 kilograms (125 pounds). On the other hand, the smaller Hydrocynus vittatus is one of the most outstanding game fishes in the world.
In the Indo-Pacific regions, marine and freshwater tigerfishes belong to the family Theraponidae in Perciformes. One common species, the three-striped tigerfish (Therapon jarbua), is vertically-lined approximately 30 centimeters (12 inches). These fishes possess sharp spines on their gill coverings, injuring their attackers or careless handlers.
Like piranhas, African tigerfishes have interlocking, razor-sharp teeth and muscular bodies, often hunting in groups, making them formidable predators.
Quick Fact — Tigerfishes are the only freshwater species recorded and confirmed to attack and catch birds while in flight.
4. Piranha (Pygocentrus)
Piranha comprises more than 60 razor-toothed carnivorous fishes native to South American freshwaters, most especially the Amazon River. Although the 1978 movie Piranha depicted them as voracious, aggressive killers, most species are scavengers or herbivores and never exceed 60 centimeters (2 feet).
Some typical features of piranhas include:
- Deep bodies
- Saw-edged bellies
- Large, blunt heads
- Powerful jaws with sharp, triangular teeth meeting in a scissors-like bite
The red-bellied piranha (Pygocentrus nattereri) has the strongest jaws and sharpest teeth, measuring up to 50 centimeters (20 inches). In deep water, it hunts in groups that can exceed 100 members. Red-bellied piranhas prefer smaller or slightly larger prey and spread out when seeking prey.
Fun Fact — When the attacking scout among piranha hunting groups locate a game, they signal the others, possibly with sound, as piranhas have outstanding hearing abilities. Subsequently, each group member approaches the game, takes a bite, and swims away, leaving room for the others.
Another species, the lobetoothed piranha (Pygocentrus denticulate), primarily occupies the Orinoco River basin and lower Amazon tributaries. Similarly, the San Francisco piranha (Pygocentrus piraya) is native to the San Francisco River in Brazil. Both species are dangerous to humans.
Most piranha species never kill enormous animals, and their piranha attacks on individuals are severe but relatively rare. Although attracted to the smell of blood, most species scavenge more often than they kill.
3. Stonefish (Synanceia verrucosa)
Stonefishes are venomous marine fishes belonging to the family Synanceiidae. They inhabit the tropical Indo-Pacific’s shallow waters. Dwelling in the bottom of the water, they’re sluggish and live among rocks or coral and in estuaries and muddy waters.
Several characteristics of stonefish include:
- Large heads and mouth
- Small eyes
- Rocky skins with wart-like lumps
- Fleshy flaps
They’re thickset fish that rest motionless on the bottom of water bodies, blending with their surroundings in both form and color. Remarkable as dangerous fish, they stay in places difficult to see.
When people step on them, they inject doses of venom into the individuals through grooves in their dorsal-fin spines. The resulting injuries are severely painful and sometimes fatal.
2. Atlantic Manta Rays (Mobula)
Manta rays are Chondrichthyes in the family Mobulidae. The group termed manta rays or devil rays consists of various marine rays.
With its members flattened and broader than long, they have large fleshy pectoral fins resembling wings. Their pectoral fins possess extensions, identical to a devil’s horns, projecting from the anterior aspect of their head.
Devil rays also have short whip-like tails equipped, in several species, with stinging spines. They’re related to skates and sharks and occupy warm waters across continents and islands.
Capable of propelling themselves by flapping their pectoral wings, they swim at or close to the water surface. They sometimes leap or somersault out of the water and consume plankton and little fishes, sweeping them into their mouths cephalic fins.
The smallest manta ray species (Mobula diabolis), a cartilaginous fish found in Australia, doesn’t grow more than 60 centimeters (2 feet). However, the oceanic manta ray (Mobula birostris), also known as the giant devil ray, or simply Atlantic Manta, can grow beyond 7 meters (23 feet) in width.
Atlantic mantas are famous brown or black ray species. They’re significantly powerful but inoffensive when they aren’t threatened. Contrary to popular tales, they don’t envelop divers and devour them.
Fun Fact — Atlantic mantas are the fishes with one of the largest brains, with their brain weighing up to 200 grams, five to ten times larger than a whale shark’s brain. They have the most significant brain-to-mass ratio of any currently known fish. Seemingly demonstrating self-awareness, they’re among the few animals that may pass the mirror test. They also heat the blood going to their brain.
1. Electric Eel (Electrophorus electricus)
The electric eel is an elongated, cylindrical fish species native to South America. The fish generates a potent electric shock to incapacitate its prey, typically other fish. With a long, scaleless, and mainly gray-brown body, and an occasional red underside, it grows to 2.75 meters (9 feet) and weighs 22 kilograms (48.5 pounds).
The electric eel’s tail region is the longest part, constituting about four-fifths of its total length. It’s bordered along the bottom by an undulating anal fin used to propel the creature.
Although called an eel, electric eels aren’t true eels. Instead, they’re a knifefish more related to the characin fish, including piranhas and neon tetras.
Electric eels are among the chief aquatic predators of the várzea, a whitewater-flooded forest in the Amazon biome. In one fish study of the várzea forest, electric eels were found to constitute more than 70 percent of the fish biomass.
They’re typically sluggish fishes, preferring slow-moving freshwater, where they regularly swim to the surfaces to gasp air. Their mouth is richly vascularized, thus allowing them to use their mouth as a lung.
Fun Fact — Electrophorus electricus have three pairs of abdominal organs involved in electricity production. They include the main organ, Sach’s organ, and Hunter’s organ. Consisting of electrolytes, they enable the electric eel to produce high-voltage and low-voltage electric shocks.
The tendency of electric eels to shock their prey may have developed to protect their delicate mouth from injuries stemming from struggling spiny fishes. Consequently, the shocked prey is disoriented long enough for the electric eel to suck it through its mouth to its stomach.
Occasionally, the electric eel doesn’t bother to shock its prey but rather gulps them quicker than they can react. The electrical discharges may also be employed to prevent the potential game from escaping or elicit a shudder response in unseen prey that prompts the prey to give up its location.
An electric eel’s tail region comprises electric organs derived from muscle tissue and innervated by spinal nerves. These organs discharge 300–650 volts of electricity — a charge sufficiently potent to jolt humans.
Although human deaths from electric eel shock are relatively rare, multiple shocks may result in respiratory or heart failure in humans. Humans have also been known to drown in shallow water after a sudden stunning jolt from an electric eel.
Frequently Asked Questions (FAQ)
What’s the most dangerous fish in the world?
The electric eel is the world’s most dangerous fish with its ability to jolt humans with electric shocks.
What’s the most dangerous river fish in the world?
Piranhas, various razor-toothed carnivorous fishes inhabiting the Amazon river, are among the most dangerous river fishes on the Earth.
What’s the most dangerous freshwater fish in the world?
Electric eels and piranhas are the planet’s most dangerous freshwater fishes.
What’s the most dangerous fish in the sea?
With a potent venom that can leave humans in intense pain or even cause death, stonefish are the most dangerous fish in the sea.
What’s the most dangerous fish to eat?
Moray eels and puffers are dangerous to eat because of the high levels of toxins concentrated in their internal organs.
While fishes may seem like the most vulnerable vertebrate group, various species are exceedingly dangerous and capable of defending themselves. Individuals should be careful when aboard a ship or boat and when swimming to prevent dangerous or even fatal fish attacks.
It’s also vital for anglers, fish fanciers, and ichthyologists to apply caution when handling harmful fish species. More importantly, fish attack victims should seek medical or therapeutic help as soon as possible.