The Poison Control Center

An Overview of Fish Poisoning and Envenomations

There are over 200 species of venomous marine fish. Venomous fish can inject toxins into our bodies when we come in contact with them. Poisoning can also occur by ingesting the flesh of a toxic fish.

Species such as the scorpion fish, stonefish and lionfish, are found in the Pacific Ocean, Australia and the temperate waters of the tropics. The spikes on these fish will sting a human; the sting is considered severe and requires treatment and possibly hospitalization depending on the species. A sting from the spikes of the scorpion fish can cause intense excruciating pain and other complications like weakness, dizziness, shock, edema and respiratory distress.1 If there are no systemic symptoms present, the sting can be managed at home with hot water immersion to relieve the pain.


Jellyfish are a well known venomous marine species in the United States. The jellyfish found along the coasts of the United States are not deadly although they can cause severe pain at the site of envenomation, nausea, vomiting and headaches.2 Several calls a year are received at the Philadelphia Poison Control Center (PCC), usually during the summer months, in reference to jellyfish stings. The traditional treatment for relief of the sting has been household vinegar.4 Application of vinegar for 30 seconds to the site of the sting will inactivate any tentacles adhering to the skin.3 To prevent further envenomation, always remove any remaining tentacles.  A cold pack is also recommended for pain relief.2 Baking soda paste is another household remedy used to apply to the wound for pain relief and removal of any remaining nematocysts.4

The Chironex fleckeri of the chirodropid species, also known as the sea wasp or the box jellyfish, is considered the most deadly jellyfish in the world.3 Stings from its tentacles cause an erythematous whipped appearance on the skin and may result in blackening and necrosis in the area. This deadly species of jellyfish is only found in certain areas of the world, mainly in Australia.6 There have been over 60 deaths from C. fleckeri in tropical Australia over the last century.11 The early systemic symptoms of envenomation include dizziness, confusion and agitation and unconsciousness and can occur within minutes. The Chironex fleckeri will cause death within five minutes due to cardiac dysfunction or arrest if untreated. The treatment for its deadly sting is removal of tentacles with vinegar, compression bandages, parenteral narcotics for severe pain. It is not uncommon for a patient with box jellyfish stings to be beyond resuscitation by the time medical help arrives. Those patients lucky enough to have survived the sting will receive a rapid IV administration of the antivenin.4 Anaphylaxis can occur with administration of the sheep derived antivenin (available for primary use against the Chironex fleckeri). Its use is controversial concerning the efficacy in saving lives after a C. fleckeri envenomation.3,6,11

Stingrays and skates

Marine envenomations in the United States and worldwide include those from stingrays and skates. Calls have come into the Philadelphia PCC during the summer months involving injuries inflicted from people accidentally stepping on the stingray or being slashed by the tail. The three most common stingrays are the round stingray, Urolophus halleri, found along the Pacific coast from California to Panama; the blunt-nosed stingray, Dasyatis sayi, found along the eastern Atlantic coast of North, Central, and South America and the spotted eagle ray, Aetobatus narinari, found throughout the tropical waters from the Atlantic to the Pacific.4

When stepped on, the ray strikes upward and drives the spine deeply into foot or leg. As the stinger enters the flesh, the integumentary sheath surrounding the spine is ruptured and the venom escapes into the victim's tissues.5 Stingray venom is one of the most powerful vasoconstrictors found among the natural toxins. It is primarily made up of protein and the extracts contain serotonin and enzymes such as 5’-neucleotidase and phosphodiesterase.4

The venom from a stingray can cause severe pain from six to 48 hours, with the greatest intensity of the pain within 30 to 60 minutes. Systemic effects of the venom can cause cardiovascular effects such as coronary artery spasm, hypotension, syncope and peripheral vasoconstriction.4, 5 It can also cause arrhythmia, respiratory distress, sweating, nausea, vomiting, weakness and abdominal pain.5 Treatment includes care of the wound, relief of pain, hot water immersion, observation and hospitalization in severe cases. Continuous hot water immersion of the wound for 60 minutes is recommended for relief of pain and is considered the standard of care. Tetanus prophylaxis and antibiotic coverage is usually required because these wounds are prone to infection.4

Toxic algae

Toxic algae appear to be increasing worldwide as coastal pollution increases.4 Many fish poisoning are likely to occur from the result of ingesting fish toxic with Harmful Algal Blooms (HAB). Harmful Algal Blooms are defined as a variety of microscopic and macroscopic marine algae that produce toxic effects on humans and other organisms; physical impairment of fish and shellfish; nuisance conditions from odors and discoloration of waters or habitats.7 HAB can cause neurotoxic shellfish poisoning (NSP), paralytic shellfish poisoning (PSP) and amnesic shellfish poisoning (ASP) in humans. These poisons can cause mild to severe symptoms and in certain concentrations some may be lethal to humans.8

Paralytic shellfish poisoning

Paralytic shellfish poisoning (PSP) has been reported to occur after eating pufferfish, filter feeding shellfish and mollusks. There are approximately 10 outbreak-associated PSP cases reported to the CDC each year.9  Algae of the genus Alexandrium are responsible for seasonal outbreaks of PSP along the New England coast from Maine down to New Jersey and on the West Coast from Alaska to Northern California. 7 If ingested by humans, PSP produces neurologic symptoms such as tingling and burning of the mouth and tongue, numbness, drowsiness and incoherent speech. These symptoms occur within 30 minutes to two hours after ingestion and in severe cases causes ataxia, muscle weakness, respiratory paralysis and death.  The Toxic Exposure Surveillance System of the American Association of Poison Control Centers (TESS) has identified 10 illnesses of presumed pufferfish poisoning due to exposure from PSP after eating pufferfish from the area of Titusville, Florida. 9

PSP is a significant problem on the East and West Coast of the United States because it moves through the food chain, through bioaccumulation, to ultimately affect humans, marine mammals and birds.  Dinoflagellates of the Gonyaulacoid family, also known as the “red tide”, and some freshwater bacteria are responsible for forming the blooms in the water that contaminate the filter feeding shellfish (clams, mussels, and scallops) that humans consume.9 Pufferfish also eat mollusks and might accumulate or even magnify the toxin causing poisoning in humans. The toxin produced by the red tide blooms, called saxitoxin, causes PSP by blocking sodium conductance and neuronal transmission in skeletal muscles.8 Saxitoxin is not destroyed by cooking or freezing; it is heat and acid stable and does not alter the taste or smell of food. Since rapid onset of symptoms after a meal of pufferfish could indicate saxitoxin poisoning; it is recommended to call the local poison control center and go to the nearest hospital ED for evaluation.9


Tetrodotoxin is a powerful neurotoxin found in the skin, liver, ovary, intestine and muscle of the pufferfish species (globefish, blowfish, balloon fish, toadfish).  It is a heat stable, water soluble, non protein that causes toxicity by inhibition of sodium-potassium pump activity and blockade of neuromuscular transmission.10 Symptoms of tetrodon poisoning occur within minutes of ingestion and causes headache, diaphoresis, and parasthesias of the lips, tongue, mouth, face fingers and toes rapidly.8,10 Hypotension and bradycardia may occur in severe cases. Generalized weakness, malaise, loss of coordination and respiratory arrest may be present; mortality is close to 50 percent in some studies. Supportive care is the key therapy for patients with tetrodon poisoning. Removal of the toxin and prevention of further absorption are important measures. Patients with severe poisoning may require intubation to maintain airway protection.10

Ciguatera poisoning

Ciguatera poisoning is the most frequent nonbacterial food poisoning worldwide.12 More than 200 species of fish are known to cause ciguatera poisoning, the most common being grouper, red snapper, and barracuda. The incidence of ciguatera poisoning is high (between 50 and 500 cases per 10,000 population) among the endemic areas of the Caribbean and South Pacific islands.13

Ciguatera poisoning from fish is caused by a neurotoxin (ciguatoxin) present in the dinoflagellate, Gambierdiscus toxicus.13 The toxin is passed through the food chain and becomes concentrated in larger fish (greater than three kilograms) such as the kingfish and the sturgeon. The toxin is harmless to fish but poisonous to humans.14 It binds to the voltage-gated sodium channels in the nerves and muscles of the body and increases the sodium permeability of the channel.10, 15 Ciguatoxin is similar to the others in that it is tasteless, odorless, heat and acid stable, and is not destroyed by cooking or freezing.10,14 But it differs in the symptoms that are produced. Within the first one to six hours after ingesting the fish (Phase I), gastrointestinal symptoms such as abdominal pain and cramping, profuse watery diarrhea, nausea and vomiting can occur. Phase II, six to 12 hours post ingestion involves significant neurological symptoms like tingling in the lips and tongue, parasthesias in the extremities and a strange metallic taste in the mouth.10,16

A characteristic symptom of ciguatera poisoning is heat-cold reversal. Patients describe the feeling as burning or extreme warmth superficially, but cold under the skin.10 At 12 hours post ingestion (Phase III), weakness, ataxia, hypotension and dysesthesia are observed. The toxin is usually eliminated through vomiting (40 percent) and diarrhea (70 percent) but there may be some limited benefit in administration of activated charcoal to the patient.16 The GI symptoms usually subside within a 24-hour period but the neurological symptoms may persist for days to months.10,13 Fluid and electrolyte repletion is recommended for patients with significant GI fluid loss.  IV mannitol (1g/kg over 30 to 45 minutes) has been used to decrease the neurologic and muscular symptoms associated with ciguatera poisoning.10,15 Mannitol therapy has gained acceptance as the treatment of choice in ciguatera poisoning but it is also controversial whether it has any therapeutic benefit.8,10,15,16 Gabapentin is also used for the treatment of ciguatera poisoning but its efficacy is questionable.13

Domoic acid

Domoic acid is produced by the diatom Nitzschia pungens and has been isolated in shellfish from Prince Edward Island, Canada.10 This toxin is responsible for amnestic shellfish poisoning (ASP) in humans causing symptoms of gastroenteritis and neurotoxicity. Symptoms occur within 15 minutes to 38 hours post ingestion of filter feeding shellfish (mussels, clams) from endemic areas.8,10 Neurotoxic findings of ASP include mutism, hemiparesis, memory loss, purposeless chewing, coma and seizures. Up to10 percent of ASP patients may suffer long term antegrade memory deficits as well as motor and sensory neuropathy.10


Poisoning that occurs from fish and other marine species can be prevented and managed. In the case of marine envenomations, take caution in waters with known infestation of jellyfish and or sting rays. Aquarium owners should not handle any known poisonous tropical fish (dead or alive). Basic measures at the time of envenomation can provide initial pain relief and prevention of further envenomation. When eating fugu (a Japanese pufferfish delicacy) or other pufferfish species, always make sure that it is prepared and handled by licensed professionals. Avoid eating large fish from endemic areas of ciguatoxin. If neurotoxic symptoms appear after eating pufferfish, barracuda, red snapper or any other fish, patients should visit the nearest emergency department as soon as possible.

Clinical reviewers' comments


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  2. International Life Saving federation Medical Commission, Marine Envenomation. (accessed 2002 Aug 12)
  3. MJA: Fenner and Williamson, Worldwide deaths and severe envenomation from jellyfish stings. (accessed 2002 Aug 9)
  4. Haddad, L. and Lee, R.  Toxic Marine Life.  In: Clinical Management of Poisoning and Drug Overdose. 3rd ed.  Philadelphia: W.B. Saunders: 1998:386-397.
  5. Venomous Fish. (accessed 2002 Aug 7)
  6. CSL Antivenom Handbook-Box Jellyfish Antivenom. (accessed 2002 Aug 12)
  7. University Systems of Maryland: Fish Health in the Chesapeake Bay. Harmful Algal Blooms. (accessed 2002 Aug 6)
  8. Kim, S. Food Poisoning: Fish and Shellfish. In: Poisoning and Drug Overdose. 3rd ed. Olson K, ed. Stamford: Appleton and Lange: 1999:175-176.
  9. Centers for Disease Control (CDC): Morbidity and Mortality Weekly Report (MMWR): Neurological Illness Associated with Eating Florida Pufferfish, 2002. (accessed 2002 April 21)
  10. Tunik, J and Goldfrank, L. Food Poisoning. In: Goldfrank’s Toxicologic Emergencies. 6th ed. Stamford: Appleton and Lange: 1998:1167-1176.
  11. Currie, BJ.  Clinical Toxicology: A Tropical Australian Perspective. Therapeutic Drug Monitoring. 2000; 22(1): 73-78.
  12. Treatment of Ciguatera Fish Poisoning. Neurology. 2000; 58(6): 843-844.
  13. Perez C, Vasquez P, Perret C. Treatment of Ciguatera Poison with Gabapentin. New England Journal of Medicine. 2001; 344(9): 692-693.
  14. Travel Medicine Program (TMP): Population and Public Health Branch: Travel Health Advisory. Ciguatera Fish Poisoning. (accessed 2002 Aug 6)
  15. Schnorf, H, Taurarii, M, Cundy T. Ciguatera fish poisoning: A double-blind randomized trial of mannitol therapy. Neurology. 2002;58(6): 873-880.
  16. Leikin, J and Paloucek, F. Ciguatera Food Poisoning. In: Poisoning and Toxicology Compendium. Cleveland: Lexi-Comp Inc.: 1998: 783.


Alana Houston, PharmD candidate, University of the Sciences in Philadelphia, August 2002

Clinical reviewers of The Poison Control Center

A. Muller, S. Sheen

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