Marine Poisonings

Marine Toxicology

Weever Stings and Other Poisonous Fish

A large number of fish, mollusks, anemones, and other marine organisms can cause toxic reactions upon contact with humans. Of the approximately 27,000 known species in the ocean, about 1,700 are considered more or less poisonous. This number exceeds the combined number of all known poisonous vertebrates. Poisoning from marine species can occur after consuming toxic fish or after stings or contact, usually from venomous spines. The most common poisonings from fish consumption are scombroid poisoning, ciguatera poisoning, and fugu poisoning (pufferfish), with fugu poisoning being the most severe, having resulted in several deaths.

It is becoming increasingly common for Swedes to dive or swim in tropical waters, exposing themselves to various poisonous marine species. Consumption of toxic exotic fish has also become more common in Europe due to imports. Several cases of ciguatera poisoning have been reported in Germany in recent years.

For information on other toxic marine animals and algae, please refer to the treatment overview:
Jellyfish, Algae, and Toxic Marine Animals

Greater Weever (Trachinus draco)

The greater weever is an edible fish found along the Swedish west coast down to the Öresund, most commonly in Bohuslän.

Description

The greater weever is long and slender, typically a few decimeters long. It has a shimmering green, yellow, and black pattern on a yellow-green background. The mouth is upward-facing, giving the fish a slightly sulky appearance.

The weever has venomous spines on its back and gill fins. It can inject venom, primarily from its dorsal fins. The fish has two dorsal fins, with the front one being venomous. The toxin is hemorrhagic, neurotoxic, and necrotizing. Unlike lionfish, the weever does not attack but only stings in self-defense.
External link to image of greater weever from the Swedish Agency for Marine and Water Management website

Risk of Sting

The weever moves toward the coast in spring and remains near the shores during summer when most stings occur. The fish hides in the sand on the seabed, with only its eyes and mouth visible, waiting for prey.

• Stings commonly occur when fishers clean their nets after catching weevers and accidentally touch the venomous spines with their fingers.
• It is risky to unhook a weever from a fishing line, as stings can occur. Note that the gill fins, not just the dorsal fins, have venomous spines!
• Foot stings can happen if someone steps on a weever.

The weever’s venom remains active even after the fish has died. A sting from a weever results in severe inflammation, causing pain, swelling, and numbness. Despite its venom, the weever is a fine food fish (similar in taste to sole) and can be purchased from fish markets.

Lesser Weever (Echiichtys vipera)

Along the Danish west coast in the Atlantic, there is a smaller variant of the weever called the lesser weever. This fish is also found in the English Channel, the eastern Atlantic, along the French west coast, in the Black Sea, and in the Mediterranean.

The lesser weever is considered Europe’s most dangerous fish. It is about 15 cm long and sand-colored, with a black dorsal fin equipped with venomous spines. The spines are sharp enough to penetrate a wetsuit or flip-flop sandals. The lesser weever’s toxin contains more serotonin than its larger relative, which is believed to explain the more pronounced pain associated with stings from this fish.
External link to photo of lesser weever

Symptoms

Common symptoms of weever stings include:

• intense pain
• swelling
• numbness
• loss of sensation
• skin discoloration

Additional general symptoms may include:

• nausea
• general discomfort
• headache
• dizziness
• chills
• sweating
• drowsiness
• generalized seizures (in rare cases)

While the sting is not typically life-threatening, bacterial infections can develop in the affected skin, complicating the course of recovery.

Sensory loss after a weever sting is usually temporary but can persist or even become permanent in rare cases. Swelling may last for a prolonged period, often up to a month, and in some cases, up to a year. However, the toxin only remains active for a maximum of 48 hours.

Treatment

• The affected body part should be immersed in hot water (at least 40°C) immediately after the sting to inactivate the toxin (denature the protein) and achieve immediate and effective pain relief. The water should be around 45°C, and care should be taken to avoid scalding. The affected area should be kept in the warm water until lasting pain relief is achieved. The treatment should last at least 30 minutes but may need to continue for up to 90 minutes. Refill the container with fresh hot water during the treatment and, if possible, use a water thermometer to monitor the temperature.
• If any venomous spines remain in the wound, they should be removed, possibly through surgical intervention. If difficult to locate, ultrasound may help detect the spines.
• The affected area should otherwise be left alone, and the wound should be kept clean.
• Antibiotics are only administered if a secondary infection occurs, which is not uncommon.

Seek medical attention if:

• General symptoms develop.
• Persistent, severe pain occurs.
• Surgical removal of a venomous spine is required (ultrasound may help locate the spine).

Stonefish (Synanceia verrucosa)

The stonefish is a highly venomous fish found in the tropical parts of the Indian Ocean and the Pacific. Stonefish grow up to 30-60 cm long and are ambush predators, quickly attacking and consuming small fish. They can harm humans through stings from their venomous spines.

The stonefish belongs to the scorpionfish family (Scorpaenidae) and is considered one of the most venomous fish. Several deaths have been reported, some occurring within an hour after the sting. There are several subspecies of Synanceia, including Synanceia verrucosa, Synanceia erosa, and Synanceia trachynis, varying in size.

Description

The stonefish has a highly developed camouflage, making it very difficult to spot, even when looking directly at it. The fish often hides in the sand, with only its mouth and eyes visible. Its warty appearance makes it blend in with surrounding rocks and algae. The stonefish has 13 venomous spines on its dorsal fins, which it raises immediately when approached, touched, or stepped on. Its venom is complex, containing neurotoxins, myotoxins, and proteins that cause a strong antigenic reaction. Antivenom for stonefish venom is available and can be used for systemic treatment in cases of severe symptoms following a sting.

Symptoms

The venom from the stonefish is extremely toxic, and a sting causes immediate, severe pain.

Common symptoms include:

• intense pain
• swelling
• numbness
• loss of sensation
• skin discoloration

Additional general symptoms may include:

• nausea
• general discomfort
• headache
• dizziness
• chills
• sweating
• blood pressure drops and seizures (in rare cases)
• circulatory and respiratory complications in severe cases

The venom can be fatal, causing rapid deterioration within minutes. Deaths have occurred within an hour after a sting.

Treatment

• The affected body part should be immersed in hot water immediately after the sting. This inactivates the toxin (denaturing the protein). The water should be around 45°C, and the affected area should be kept in the warm water for 30-90 minutes, until lasting pain relief is achieved.
• Tetanus immune globulin (250 IU intramuscularly) should be administered if tetanus protection is lacking; otherwise, give tetanus vaccine subcutaneously (recommended, though scientific evidence is limited, as tetanus cases have been described).
• For severe systemic symptoms or shock, treatment with specific antivenom for stonefish venom should be given.

Lionfish (Pterois volitans)

The lionfish is a striking, zebra-like fish found among coral reefs in the Indian Ocean and the western Pacific. It can cause poisoning through its venomous spines. It is also found along the U.S. east coast. In Sweden, the lionfish is only present in aquariums.

The lionfish belongs to the genus Pterois, which is a subgroup of the scorpionfish family (Scorpaenidae).

Description

The lionfish can grow up to 38 cm and weigh up to 1 kilogram, but it is usually somewhat smaller. It is a beautiful fish with brown and white stripes, sometimes referred to as the “zebra fish” or “lionfish.”

The lionfish hunts fish and crustaceans at night, hiding among coral reefs during the day. Its large pectoral, pelvic, and dorsal fins move slowly, resembling elegant veils.

The lionfish has venomous glands in the first three dorsal spines, which secrete a neurotoxic venom. Local and systemic symptoms may develop. The venom contains inflammatory substances such as prostaglandins and thromboxane B2.

The lionfish can actively sting with its dorsal spines when threatened. Stings commonly affect the lower limbs. In Sweden, most injuries are reported among those working with aquarium fish.
External link to a photo of a lionfish, Wikipedia

Symptoms

The venom glands of the lionfish are smaller than those of the stonefish. Although the venom is highly toxic, the sting primarily causes intense, immediate pain.

Common symptoms, besides pain, include:

• swelling
• numbness
• loss of sensation
• skin discoloration

Additional general symptoms may include:

• nausea and vomiting
• general discomfort
• headache
• dizziness
• chills
• sweating
• drowsiness
• circulatory and respiratory issues (rare cases)

Deaths are extremely rare but can occur. The venom remains active even after the fish is dead and can survive freezing. Secondary infections are common after stings.

Treatment

The affected body part should be immediately immersed in hot water. This inactivates the toxin (denatures the protein). The water should be at least 40°C, preferably between 45°C and 50°C. The affected area should remain in the hot water for 30-90 minutes, until lasting pain relief is achieved. Ultrasound should be used to locate and surgically remove any venomous spines that may remain.

Spotted Trunkfish (Lactophrys bicaudalis)

The spotted trunkfish is a coral reef fish that secretes a ciguatera toxin when touched from glands on its back. The toxin is only dangerous when the fish is consumed, so there is no immediate danger to divers from contact. However, sharks can die after eating a trunkfish. Moray eels and many other coral fish may also contain high levels of ciguatera toxin when eaten.

Scombrotoxin Poisoning

Consumption of fish from the Scombridae and Scomberesocidae families can cause a poisoning syndrome known as scombrotoxin poisoning or scombroid poisoning. The syndrome commonly occurs after eating various species of tuna or mackerel, such as skipjack tuna or bonito. These fish are often consumed in salads, particularly in the Mediterranean region.

Scombrotoxin poisoning occurs after eating fish contaminated with bacteria that release large amounts of histidine. The bacteria include E. coli, Proteus, Klebsiella, and Aerobacter. In these bacteria, histamine and histamine-like substances (histidine) are produced by the enzyme histidine decarboxylase.

Scombrotoxin poisoning is not an allergic reaction, but the symptoms are similar.

Symptoms

Symptoms usually appear within an hour after consumption. The symptomatology is related to histamine release and includes:

• sweating
• nausea
• vomiting
• diarrhea
• headache
• palpitations
• flushing (redness)
• hives
• dizziness
• swelling of the face, lips, and tongue (in rare cases)

Respiratory problems can occur, such as bronchoconstriction and a drop in blood pressure. Symptoms are usually short-lived and subside within 8-10 hours.

Treatment

• Treatment with antihistamines that block H₁ and H₂ receptors is recommended, such as cimetidine (Tagamet) 400 mg x 2.
• Cortisone is not indicated and may, in fact, prolong the course.
• Severe cases must be treated with intravenous fluids, antihistamines, and adrenaline.

Ciguatera Poisoning

Poisoning can occur after consuming fish belonging to the ciguatera genus. These fish are mainly found in the West Indies and the Caribbean Sea. They include Napoleon fish, parrotfish, barracuda, tropical sea bass, red snapper, amberjack, kingfish, and other exotic fish that live around coral reefs. Ciguatera poisoning is common in and around the Dominican Republic. Parrotfish can also contain tetrodotoxin, which is significantly worse.

Ciguatera toxin originates from toxin-producing algae found in coral reefs and has moved up the food chain. The fish smells and tastes normal. The toxin concentration is highest in the liver and intestines of the fish.

Symptoms

Common symptoms include:

• nausea
• vomiting
• diarrhea
• general malaise, fatigue, and drowsiness
• myalgia, neck pain
• chills and sweating
• neurological symptoms (polyneuropathy), paresthesia, numbness, and loss of sensation in the extremities, mainly the lower ones, but cranial nerve involvement can also occur
• pain, aches, and muscle weakness
• metallic taste in the mouth
• pain upon cold contact, allodynia
• blood pressure drop, bradycardia
• coma in severe cases

Gastrointestinal symptoms last for 1-2 days, while other symptoms last up to a week. Neurological symptoms can be prolonged and, in rare cases, permanent. This is referred to as chronic ciguatera poisoning, which may result in allodynia and chronic pain. Clinical neurophysiology tests may show reduced nerve conduction in the affected limb.

The diagnosis is made based on the patient’s history and clinical presentation. Ciguatera toxin testing in humans is under development but not yet an established method. However, fish remnants can be analyzed to confirm the presence of ciguatera toxin. This should be done if multiple people have been poisoned, and health authorities should be notified.

Treatment

Primarily symptomatic, with rest and intravenous fluids if necessary. Intravenous Mannitol (1 g/kg) has shown good effects on neurological and muscular symptoms in several case reports when administered within 48 hours of onset. However, the scientific evidence for mannitol treatment is weak, and the treatment has been questioned. No other specific treatment is available. Antihistamines may help, as well as common analgesics like paracetamol (Alvedon) for pain.

Fugu Poisoning

In Japan and some other Asian countries, pufferfish, Fugu, is considered a delicacy when prepared correctly. Several species of pufferfish include Takifugu rubripes, Lagocephalus, and Sphoeroides. Pufferfish live in the Pacific Ocean, the Red Sea, and the Indian Ocean. They are primarily found around Japan, China, the Philippines, and Taiwan but also in the West Indies and Mexico. Pufferfish are also called knobby tetraodontid fish due to their knobby appearance and four strong teeth. Poisoning occurs after consumption.

Link to image of Fugu

The fish contains a potent toxin, tetrodotoxin, which can cause severe neuromuscular poisoning and even death. Tetrodotoxin is a neurotoxin that can cause paralysis. The toxin binds to sodium channels in peripheral nerve cells and blocks neurotransmission. Ten milligrams is considered a lethal dose. It does not cross the blood-brain barrier but mainly causes peripheral paralysis, including respiratory paralysis. Tetrodotoxin is also found in other marine species like the blue-ringed octopus, parrotfish, and certain frog species (poison dart frogs). The toxin is concentrated in the fish’s internal organs, mainly the liver but also the intestines, gonads (ovaries), and skin. The pufferfish’s spines are not poisonous, but the toxin is present throughout the fish.

From 1974 to 1983, 646 cases of Fugu poisoning were reported in Japan, with 179 deaths. In severe poisoning cases, the mortality rate is estimated to be close to 50%, with paralytic paralysis and respiratory failure. The poisoned patient may develop total paralysis but remain awake and conscious until close to death. Death usually occurs within 4-6 hours of consumption, with a range of 20 minutes to 8 hours. Patients die from respiratory paralysis and asphyxiation. With artificial ventilation, mortality has dropped to around 5%. There is no antidote. The toxin is likely produced by bacteria that the fish eats, such as Vibrio alginolyticus.

Symptoms

Common symptoms of Fugu poisoning include:

• numbness around the mouth and lips
• progressive loss of sensation in the face, arms, and legs
• a feeling of numbness and lightheadedness
• headache
• abdominal pain
• nausea
• diarrhea
• progressive neuromuscular paralysis
• hypoventilation
• hypoxia
• hypercapnia
• seizures
• mental dullness
• heart arrhythmias
• cardiovascular collapse

Treatment

There is no specific antidote. Treatment is primarily symptomatic, focusing on artificial ventilation and following general intensive care principles. Since neuromuscular paralysis is common, it is crucial to support breathing and initiate mechanical ventilation and respiratory treatment as soon as possible. Treatment with intravenous fluids and inotropic drugs follows standard intensive care practices.

Stingray

This beautiful fish has caused several dangerous poisoning incidents through stings with its tail fin, often involving overly curious divers. The stingray is a cartilaginous fish and a freshwater fish found in South American rivers. Injuries usually occur when someone accidentally steps on a stingray, as they do not typically attack humans. A sting can cause pain, swelling, tenderness, and, not infrequently, secondary infections. Muscle cramps and general symptoms can occur. The sting is usually not life-threatening unless vital organs are damaged. A part of the fin may remain in the wound and should be surgically removed. Treatment with hot water (45°C for 30 minutes) on the affected body part can be tried, as with other marine stings.

ICD-10

• Fish poisoning caused by ciguatera T61.0
• Fish poisoning caused by scombroid T61.1
• Toxic effect of contact with fish T63.5

Jellyfish, Algae, and Toxic Marine Animals

A large number of fish, mollusks, anemones, and other marine organisms can trigger a toxic reaction when in contact with humans, usually through stings. Of the ocean’s approximately 27,300 known species, around 1,700 are considered more or less toxic. This is more than all known toxic vertebrates combined. About 9,000 different marine species are cnidarians (Cnidaria), named from the Greek word for “sting.” The cnidarian group includes jellyfish, coral animals, and hydras. All cnidarians are a type of predator that capture and consume prey.

An estimated 80,000 people suffer from various conditions caused by toxic marine animals each year. Most of these are skin irritations caused by nematocyst contact when an inflammatory toxin is released from cnidarians.

This guide describes the most common toxic organisms, excluding fish, found in Swedish waters and some that we may encounter in exotic locations. It is becoming more common for Swedes to dive or swim in tropical waters and be exposed to various toxic marine species. In the Mediterranean, there has been a dramatic increase in the number of jellyfish in recent years.

For more information on poisonous fish, see also:

View overview: Greater weever sting and other poisonous fish

Cnidarians are divided into four classes: anthozoans (Anthozoa), jellyfish (Scyphozoa), box jellyfish (Cubozoa), and hydrozoans (Hydrozoa).

• Anthozoa: coral animals lacking a medusa form. Solitary or colonial polyps.
• Scyphozoa: jellyfish, polyps in medusa form, ring jellyfish, lung jellyfish, and disc jellyfish.
• Cubozoa: box jellyfish with several subspecies.
• Hydrozoa: a species-rich and highly diverse subgroup of cnidarians. Colonial, e.g., Portuguese man-of-war.

Jellyfish (Scyphozoa)

Jellyfish are free-swimming medusas, bell- or saucer-shaped, with a ring of tentacles below them. The edges of the mouth on the underside are extended into mouth tentacles or arms that hang (trail) below the animal. A small number of different jellyfish naturally occur in Swedish sea waters. Moon jellyfish, red lion’s mane jellyfish, and blue jellyfish are found along the west coast, in Kattegat and Skagerrak. Compass jellyfish and lung jellyfish can also be seen here. Of these, only moon jellyfish occurs in the Baltic Sea.

In our waters, it is primarily the red lion’s mane jellyfish that causes harm to humans, but the blue jellyfish and compass jellyfish also have cnidocytes that can cause skin irritation. The jellyfish found in Sweden mainly cause local symptoms in the form of burn-like skin irritation. In tropical countries, significantly more toxic jellyfish exist that can cause general symptoms in addition to pronounced local symptoms.

Background

Jellyfish are a type of invertebrate, soft cnidarian that mainly consists of water, bound in a gel-like body. The upper part of the jellyfish’s body forms the bell, and underneath the bell are several mouth arms and tentacles. A large number of stinging threads hang and trail from the bell.

Jellyfish swim by rhythmically contracting the bell, which creates a propulsive jet, but jellyfish mainly follow water currents passively. The long tentacles trail after the body and are used to catch prey, which is stung, broken down, and digested.

Jellyfish primarily occur during the summer and autumn in Swedish sea waters. Jellyfish live in two phases: first as polyps attached to the bottom, and then as free-swimming medusas. The free-swimming phase begins in spring when the jellyfish buds off from its polyp phase, after which the jellyfish lives in medusa form for about a year.

The red lion’s mane jellyfish is called “Lion’s Mane Jellyfish” in English, which aptly describes its appearance. The largest red lion’s mane jellyfish found had a diameter of 2.3 meters and 36.5-meter-long tentacles. Very large red jellyfish are mostly found in the open Atlantic, while along the coast, they rarely exceed 50 cm in diameter. The normal size is about 20-30 cm in diameter. The red lion’s mane jellyfish thrives in cold water. If the water temperature rises too much (above 20 degrees), the jellyfish descends to deeper and colder waters.

Classification

There are around 200 different types of jellyfish (Scyphozoa), of which about 14 species are found in Sweden. They are divided into four main groups:

Red lion’s mane jellyfish (Cyanea capillata)

Blue jellyfish (Cyanea lamarckii)

Moon jellyfish Aurelia (Aurelia aurita)

Compass jellyfish – Chrysaora (Chrysaora hysoscella)

Lung jellyfish – Rhizostoma (Rhizostoma octopus)

Lung jellyfish – Rhopilema (Rhopilema nomadica)

Another variety of lung jellyfish has become common in the Mediterranean in recent years. They can arrive in large swarms that invade locally. Skin contact can cause a moderate burn injury.

Among the most dangerous species worldwide are the Portuguese man-of-war (Bluebottle, Physalia physalis), Box jellyfish (Chironex fleckeri), and Irukandji jellyfish (Carukia barnesi). These jellyfish cause numerous serious stings (“stingers”) and poisoning incidents each year, including deaths. See further information on each jellyfish below.

Portuguese man-of-war (Bluebottle, class: Hydrozoa)

The Portuguese man-of-war (Physalia physalis) is widespread in tropical and warm temperate seas, most commonly off the coast of Florida and southeast in the Gulf of Mexico. The Bluebottle is not a true jellyfish (scyphozoa) but a jellyfish-like colonial organism (colonial cnidarian) and is classified as hydrozoa. It is also found along the coasts of Africa, and a closely related species is found in Australia (Physalia utriculus). The Bluebottle consists of a cluster of different organisms living in symbiosis. The upper part is gel-like and gas-filled, containing carbon dioxide and nitrogen. The upper part acts as a sail that lies over the water surface and drives the Bluebottle forward.

The Portuguese man-of-war is likely the jellyfish responsible for the most serious stings of all species, including deaths. Direct contact with the tentacles causes severe pain, high fever, and intense skin inflammation. The jellyfish reaches about 30 cm in diameter and floats on the surface with meter-long thick tentacles trailing far below the surface, the bell partially floating above water.

Follow the link for a picture of a Portuguese man-of-war:

Box jellyfish (class: Cubozoa)

The Australian box jellyfish, the “Box Jellyfish” (Chironex fleckeri), is a very dangerous jellyfish. The box jellyfish has a transparent, blue-tinged, cube-shaped bell. It is estimated to have caused around sixty deaths, mainly along Australia’s northern and western coasts. There are about 40 known subspecies, many of which are much smaller than the large box jellyfish. The jellyfish can weigh up to 2 kg, the bell can be as large as a salad bowl, and the tentacles grow up to 2 meters long. The cubic bell has four long tentacles covered with dangerous cnidocytes.

The box jellyfish moves relatively quickly, with its tentacles trailing in the water. Each tentacle contains millions of stinging capsules (nematocysts), which can cause severe burns and intense pain upon contact. It is estimated that the jellyfish has no fewer than 5 billion nematocysts in total.

Irukandji jellyfish (class: Cubozoa)

The Irukandji jellyfish (Carukia barnesi) is a dangerous little “stinger,” significantly smaller than the box jellyfish, with a bell about the size of a wristwatch face (about 2 cm in diameter). It is mostly found in Australia, particularly in northern Queensland. The Irukandji jellyfish usually inhabits deeper waters but may be swept toward beaches after storms. The jellyfish often appears in schools or groups.

Contact with the Irukandji jellyfish can cause more general symptoms, including nausea, general malaise, and disorientation. The toxin releases catecholamines, which cause a significant increase in pulse and blood pressure, and heart arrhythmias may occur. Symptoms can begin 30 minutes after contact, starting with intense pain that gradually worsens. The affected body part swells noticeably as the pain intensifies.

In the northern Mediterranean, along the coasts of Spain, France, and Italy, there are many jellyfish that can cause varying degrees of burns. Here is a brief description of some of them.

Pelagia noctiluca jellyfish

The Pelagia noctiluca jellyfish (Spanish: “Clavel de mar” – Sea Carnation) is pink or bluish (violet) and translucent, with multiple darker spots on the bell and tentacles. The bell is hemispherical with a diameter of 5-10 cm. It has 4 larger central mouth arms and 16 peripheral tentacles. The dark red tentacles resemble octopus arms and are heavily covered in cnidocytes. The bell contains bioluminescent cells that create a fascinating glow in the water at night or upon contact. Pelagia noctiluca jellyfish can cause relatively severe burns upon contact with the skin.

Mediterranean jellyfish (Cotylorhiza tuberculata)

Mediterranean jellyfish are commonly called “fried eggs” because they resemble fried eggs (Spanish: “Aguacuajada” or “Huevo frito”). Mediterranean jellyfish are yellow with a flat, compact bell with a central hemispherical yellow elevation, measuring 20-35 cm in diameter. Below the bell are 8 inverted mouth arms, giving the jellyfish a compact appearance. The underside of the bell with the mouth arms is whitish with dark or bluish-black spots. The bell is divided into 16 lobes. Mediterranean jellyfish cause mild to moderate burns upon contact with the skin.

Lung jellyfish (Rhizostoma pulmo)

The lung jellyfish (Spanish: “Aguamala”) is related to the jellyfish found in Swedish waters. The jellyfish is large, with a whitish-violet hemispherical bell and a blue edge band. The bell can grow up to a meter in diameter (90-100 cm). The bell has blue-violet lobes without stinging threads but with 8 compound mouth arms. The mouth arms form a whitish, solid mouth base. Lung jellyfish cause only mild burns upon contact with the skin.

Compass jellyfish (Chrysaora hysoscella)

Compass jellyfish are found in both the Mediterranean and northern seas (Spanish: “Compases”). They have a whitish to yellowish translucent bell with a diameter of up to 30 cm. The bell has darker radial lines that make it resemble a compass. Compass jellyfish cause relatively severe burns upon contact with the skin.

By-the-wind sailor (Velella velella)

The by-the-wind sailor jellyfish is small, 1-5 cm thick or wide, with a gel-like body that it uses as a sail above the water surface for movement (Spanish: “Velero”). The sail is covered with a whitish membrane. The bell is violet or bluish and translucent. Around the body is a blue-violet ring of relatively short threads. It resembles but should not be confused with the much more dangerous Portuguese man-of-war. The by-the-wind sailor is harmless upon contact with the skin.

Crystal jellyfish (Aequorea forskalea)

Crystal jellyfish are translucent blue-violet jellyfish with a faint color. The body is hemispherical with radial lines (canals) and a central clearing zone. In the clearing zone, there is a triangular condensed area. The bell measures up to 15-30 cm in diameter. Below the bell, long thread-like tentacles hang. Crystal jellyfish are more common in the Atlantic than in the Mediterranean. These jellyfish do not cause burns upon contact with the skin.

Toxicity

Jellyfish cause toxic injuries by coming into contact with human skin using their tentacles and stinging threads. On the tentacles and stinging threads are cnidocytes containing small sacs, nematocysts. In these nematocysts are barbed threads that, upon skin contact, shoot into the skin like a harpoon, releasing a toxin. Nematocysts can lodge in the skin by the thousands, and reactions can continue if the skin is rubbed or if the nematocysts lyse. Early rinsing of the skin aims to remove untriggered nematocysts. The toxin released causes an inflammatory reaction.

Jellyfish toxin is complex and contains a variety of pro-inflammatory substances, including:

• Bradykinin
• Hemolysin
• Serotonin
• Histamine
• Prostaglandins

Contact causes varying degrees of skin inflammation, similar to a burn. The toxin increases the influx of calcium, potassium, and sodium across the cell membrane in various tissues, insensitive to organic channel blockers. The reaction occurs by increased membrane permeability, not by pore formation.

In Sweden, it is mainly the red lion’s mane jellyfish that causes injuries, but the blue jellyfish and compass jellyfish also have cnidocytes with nematocysts that can cause skin irritation.

The Portuguese man-of-war and the Australian box jellyfish can cause severe inflammation, leaving whip-like red welts over affected skin areas.

The box jellyfish’s toxin is both neurotoxic, hemolytic, and cardiotoxic. Contact with more than 1.2 meters of tentacles is considered life-threatening for the Australian box jellyfish.

The Portuguese man-of-war has tentacles that can be more than 10 meters long. These tentacles can also detach from the jellyfish and float freely in the water. The toxin is mainly neurotoxic and can cause respiratory paralysis. The tentacles are full of nematocysts. Inflammation can become so severe that permanent scars can form, leading to skin contractures, similar to burn injuries. The Irukandji jellyfish’s toxin is also neurotoxic.

Symptoms

Symptoms of contact with jellyfish in Swedish waters are primarily local skin symptoms, such as:

• Itching, often persistent
• Redness
• Swelling
• Mild to moderate pain

In rare cases, more general symptoms may occur, such as:

• Generalized, persistent itching
• Severe pain
• Nausea, vomiting
• Drowsiness, somnolence

Moon jellyfish and lung jellyfish only cause mild skin irritation.

Contact with the box jellyfish can cause such rapid inflammation that shortness of breath, respiratory arrest, and shock may occur almost immediately, followed by cardiovascular collapse. Several cases have been described where immediate CPR at the water’s edge has been life-saving.

The box jellyfish and the Portuguese man-of-war cause immediate, severe pain upon skin contact, as well as more general symptoms, such as:

• Nausea
• Chills
• Muscle pain
• Headache
• Breathing difficulties
• Circulatory collapse

Treatment of jellyfish stings

For jellyfish stings in Swedish waters, primarily from the red lion’s mane jellyfish (Cyanea capillata):

• Rinse the affected area with plenty of seawater, but not tap water. Take three buckets of seawater and rinse the skin. Saltwater is recommended first, as freshwater causes the nematocysts in the stinging threads to lyse, releasing more toxin. Avoid showering immediately after the burn.
• You can try applying a cooling balm to the affected skin. Avoid getting jellyfish threads on your hands. Avoid vinegar, as this causes the stinging threads to lyse.
• Leftover jellyfish threads can be scraped off with, for example, a credit card. You can also remove threads with wide tape, such as duct tape. However, do not rub the skin as this may release toxins. Shaving foam and a razor can also effectively remove jellyfish threads.
• If symptoms persist, you can try immersing the affected body parts in hot water (40-45°C) to neutralize toxins. Try a hot bath for 30-60 minutes after rinsing with seawater!
• If the eyes are affected, rinse thoroughly and for a long time with tap water or, preferably, physiological saline (at least 15 minutes).
• Oral antihistamines, such as cetirizine (Zyrlex) 10 mg orally (not for children under 6 years) or loratadine (Clarityn) 10 mg x 1. For children under 2 years and weighing less than 30 kg, give 5 mg x 1. For children under 30 kg, Clarityn syrup (1 mg/ml) is recommended rather than tablets.
• The skin can be treated with a corticosteroid cream, such as Hydrocortisone CCS or Mildison, or a cooling balm to reduce the inflammatory reaction and itching. You can also try acetylsalicylic acid in cream or ointment form.
• Cold packs or lidocaine cream on painful areas can relieve the pain. Do not apply ice cubes (tap water) directly to the skin; instead, place the ice in a plastic bag.
• Symptomatic treatment otherwise.
• Vinegar, which has sometimes been recommended for applying to the skin, has been shown to lyse cnidocytes significantly and is therefore not recommended for stings from the red lion’s mane jellyfish. However, it is recommended for stings from some exotic jellyfish in other countries (scientifically unclear).

In case of an attack by a box jellyfish or Portuguese man-of-war in foreign waters:

• Immediately seek the nearest medical facility if injured by a box jellyfish or Portuguese man-of-war.
• The box jellyfish can cause respiratory arrest and cardiac arrest.
• The pain from contact with a box jellyfish or Portuguese man-of-war can be extremely severe and difficult to treat. Regional anesthesia is a possible way to block the pain using peripheral nerve blocks and local anesthetics.
• For box jellyfish stings, some sources recommend applying vinegar generously to the skin. Vinegar is said to prevent the stinging threads from lysing but does not help with already inflicted damage. Treatment with vinegar is controversial and not scientifically proven.
• Immerse the affected body parts in hot water (40-45°C) to neutralize toxins. You can try a hot bath for 30-60 minutes for extensive burns!
• Avoid rubbing the skin or applying alcohol to it.
• There is an antidote for the box jellyfish in the form of an immune serum developed using immunized sheep. Three ampoules of immune serum should be administered intravenously as soon as possible after a box jellyfish attack if general symptoms or shock symptoms are present.

Algae

Algae perform photosynthesis, but they are not plants; rather, they are a type of microorganism classified as phytoplankton. Toxic algae are primarily found in Sweden in fresh or brackish water, mainly in the Baltic Sea. These algae can produce toxic cyanobacteria, which can cause acute poisoning. The toxin-producing algae cannot survive in saltwater and are therefore not found along the west coast, in Kattegat or Skagerrak. There is an unverified hypothetical link between cyanobacteria and neurological diseases like ALS, Alzheimer’s, and Parkinson’s disease through increased production of beta-N-methylamino-L-alanine (BMAA) and increased glutamate activity in the CNS. The connection is purely hypothetical, and some research in this field is ongoing.

Algal Bloom

Algal bloom occurs offshore, along coasts, and in lakes and stagnant waterways. Algal bloom refers to a rapid growth of toxin-producing algae, usually of a single species.

Algal blooms occur primarily in sunny and calm weather when the water is unbalanced, but also due to eutrophication, mainly with phosphorus and nitrates. Abundant sunlight is needed for algal blooms. Toxic algae blooms mainly occur when water temperatures are between 15 and 23°C.

Algae counts below 10,000 cells per ml of water are generally not classified as algal blooms. In cases of significant algal bloom, there may be over a million cells per milliliter of water.

Algal blooms can often, but not always, be detected visually and by smell. Signs of algal blooms include:

• Water becomes murky with a noticeable color change, which can vary from yellow-green, blue-green, yellow-white, reddish-brown, or rhubarb-like.
• Generally, the murkiness occurs near the surface and not at depth.
• The taste and smell of the water may be affected, often smelling foul with a distinctly unpleasant odor.

Algae can bloom at any time of year, but toxic algal blooms most commonly occur in July and August, though they can extend into November. Common spring and autumn blooms are not toxin-producing and are therefore harmless to humans.

Algal blooms can lead to the production of decay bacteria, resulting in oxygen depletion in the water, which can, in turn, lead to fish deaths.

Exposure to toxic algae primarily occurs through swimming, with contact happening through the skin and mucous membranes, but also through swallowing water.

Classification

Toxin-producing algae are mainly blue-green algae, which are a variant of phytoplankton. In reality, the toxins are produced by bacteria (eubacteria), but they are classified as phytoplankton.

There are at least eight different types of toxin-producing algae in Sweden. Some of these are Microcystis aeruginosa, Anabaena sperica, Oscillatoria, and Nodularia Spumigena (cat hair algae).

The toxins are mainly classified into three categories:

• Neurotoxic toxins
• Hepatotoxic toxins
• Gastrotoxic toxins

They can also cause irritation to the skin and mucous membranes upon direct contact. In addition to toxic symptoms, they can also cause allergic reactions.

Symptoms

The clinical picture after contact typically includes rashes and gastrointestinal symptoms. Severe symptoms mainly occur if water has been swallowed repeatedly or by accident. This primarily affects animals, especially dogs.

Symptoms usually appear within a few hours after swimming, rarely later than 12 hours, and are generally temporary, resolving within a day. In severe cases, symptoms may last for 2-3 days.

There is a risk of liver and kidney damage with heavy exposure. An indication of strong exposure includes generalized symptoms such as muscle pain and joint pain. Diagnosis is based on patient history and clinical presentation.

Other animals, besides humans, are also at risk of becoming ill from contact with toxic algae; dogs, in particular, are at risk of serious symptoms after swimming among algae or swallowing contaminated water.

Common symptoms of poisoning from toxic algae include:

• Itching
• Rashes
• Eye irritation
• Nausea
• Vomiting
• Diarrhea
• Stomach pain
• Stomach cramps
• Fever
• Muscle pain
• Joint pain
• Runny nose
• Asthma-like symptoms, bronchial obstruction

Treatment

There is no specific treatment. Treatment is primarily symptomatic.

• If you have swum among toxic algae, thoroughly rinse your body with fresh water and then wash with soap and water all over your body.
• If eye symptoms occur, rinse the eyes thoroughly with running water.
• If you have swallowed large amounts of water and experience general malaise, seek hospital care. At the hospital, liver and kidney function should be checked with routine tests.
• Dogs that have swum among toxic algae should initially drink plenty of fresh water.

Sea Anemones, Corals, and Cnidarians

It is becoming increasingly common for Swedes to travel to tropical countries and dive or swim in temperate, subtropical, and tropical waters. Here, one may encounter sea anemones, corals, and cnidarians that can cause toxic reactions upon contact with their stinging cells. Therefore, it is advisable to avoid touching or breaking off corals and sea anemones.

These organisms primarily cause local symptoms through their stinging cells, but some can also cause general symptoms. The stinging cells release toxins that allow the organism to paralyze its prey before consuming it.

Classification

Anemones belong to the group of hexacoral animals and are a type of polyp with tentacles. The skin-irritating anemones belong to the phylum Cnidaria, a type of stinging animal with toxin-releasing stinging cells (nematocysts). Below are some toxic anemone and coral species. Click on the red external link for an image.

Actinodendron plumosum is a toxic sea anemone, richly endowed with nematocysts that release an irritating toxin.

Other strongly stinging anemones include Bolocera tuediae and fire coral (Millepora dichotoma, image). Stings from fire coral can cause severe burns with permanent scarring.

Treatment

Treatment is mainly symptomatic and similar to that for jellyfish stings.

• First, rinse the affected area with seawater.
• Avoid heat and sun exposure.
• Apply a corticosteroid cream or topical anesthetic containing Xylocaine.
• Oral antihistamines can help reduce the inflammatory reaction, such as Tavegyl 1-2 mg orally.

General symptoms are rare.

Palytoxin

When handling saltwater aquariums, certain implanted corals can release a toxin known as palytoxin. The corals most often involved are palythoa corals and protopalythoa corals, though some anemones can also release this toxin. Palytoxin is a potent toxin and has caused severe poisonings. Exposure to palytoxin can occur through skin contact, eye contact, ingestion, or inhalation. The toxin is a powerful vasoconstrictor and can cause vascular ischemia, including cardiac ischemia.

Symptoms of palytoxin poisoning can resemble local anesthetic overdose but primarily cause respiratory symptoms such as coughing and bronchial obstruction, gastrointestinal symptoms like nausea and vomiting, and fever. Prolonged obstructive symptoms have been reported (1-3 months). Symptoms that may occur include:

• Metallic taste in the mouth
• Tachycardia
• Shortness of breath, coughing
• Bronchial obstruction
• Fever
• Chest pain
• Hypotension
• ECG changes
• Muscle spasms
• Severe pain
• Vomiting
• Seizures

When handling these corals, it is recommended to use protective goggles, a face shield, and long gloves to avoid splashes! Treatment is mainly symptomatic and supportive, but vasodilator treatment such as with papaverine or nitroglycerin can be attempted. Avoid boiling corals from such aquariums, as the fumes can cause respiratory problems.

Cone Snail

The cone snail (Conus geographus) is a type of predatory snail that attacks and eats fish. The cone snail is large, with a cone-shaped, spotted (leopard-like), hard, and thick shell, and can grow up to 25 cm long. It often has a beautifully patterned shell, making it attractive as a collector’s item and tourist attraction. It is found mainly in the Pacific and Indian Oceans. The snail has a proboscis that it can shoot out like a harpoon from its shell to paralyze and catch its prey. Humans have also been injured by contact with the cone snail.

The cone snail injects a neurotoxic venom (conotoxin) that causes pain, paresthesia, and numbness, but also general symptoms like muscle weakness, coordination difficulties, and impaired speech, hearing, and vision. A few fatalities have been reported.

Fireworms

Chloeia Flavia
These small worms (Eng: Bristle worms/Fireworms) swim freely in tropical and warm waters and can cause burning pain upon skin contact with divers. Fireworms belong to the group polychaetes, which includes many different species. The worms have stinging cells that can cause local redness, pain, and itching. Nematocysts can be removed with tape (duct tape) from affected skin. The skin should then be rinsed, treated with vinegar, and a corticosteroid cream or local anesthetic applied. Antihistamines may slightly reduce the itching.

Blue Mussels

The blue mussel is a species in the class of mollusks. The shell of the blue mussel is blue-black and usually oval-shaped. It typically grows to about 6 cm long but can reach up to 20 cm. The edible muscle is yellowish-white.

Blue mussels are harvested intensively and cultivated on a large scale. Mussels are sold fresh, canned, or frozen. Blue mussels are a common food item after cooking. They have the best flavor in the spring.

Blooming phytoplankton that are toxin-producing can be found in blue mussels, rendering them inedible. A genus of phytoplankton (Alexandrium) has been found in such quantities among blue mussels in Bohuslän that they can cause general illness symptoms.

It is extremely rare for blue mussels to cause poisoning. Typically, toxin levels increase in the fall and are highest in winter.

Symptoms

Symptoms of consuming toxic blue mussels are primarily gastrointestinal:

• Diarrhea
• Nausea
• Vomiting

Treatment

In most cases, there is no need to seek medical attention, as symptoms are relatively mild and short-lived. In severe cases, intravenous fluids may be needed. Otherwise, treatment is symptomatic.

PSP “Paralytic Shellfish Poisoning”

More severe poisoning after consuming blue mussels has occurred when the mussels are contaminated, including with Gonyulax catenella. The most common toxin causing PSP is saxitoxin. Saxitoxin can be harbored in mussels for several weeks or longer. The toxin is produced by microscopic algae filtered through the mussel, such as after algal blooms. Other toxins that can cause poisoning symptoms include neosaxitoxin and gonyautoxin. All of these toxins are primarily neurotoxic.

Initial symptoms include nausea and vomiting, but this toxin can also cause dizziness, coordination disorders, speech difficulties, dry mouth, difficulty swallowing, difficulty breathing, increasing muscle weakness, and paralysis. There may also be hypotension, heart failure, and cardiovascular collapse. A few deaths have been reported. Children and immunosuppressed individuals are more sensitive to these toxins.

Treatment of PSP is primarily symptomatic. In severe cases, respiratory support in an intensive care unit may be necessary.

CSP (Ciguatera Shellfish Poisoning)

In French Polynesia, ciguatera-like symptoms have been reported after consuming shellfish, including oysters.

Symptoms

• Nausea
• Vomiting
• Asthenia
• Myalgia
• Paresthesia
• Dysesthesia
• Persistent hiccups

Treatment

Treatment is mainly symptomatic, but intravenous mannitol has been tried, as with ciguatera poisoning.

ICD-10

Other fish and shellfish poisoning T61.2
Toxic effect of contact with other marine animals T63.6