Monday, November 18, 2013

Top 5 Most Poisonous Fish!

By Dana Sackett

Many TV shows and nature guides have been dedicated to educating the public on the most poisonous and venomous spiders, snakes and even frogs, but what about fish? Unlike spiders or snakes, we rarely hear about which fish are the most poisonous (or venomous). This week we are dedicating our blog post to these hazardous fish.


First though let’s clarify some terminology. Poisonous and venomous are terms often used interchangeably but they have different meanings. A venomous animal has a means of injecting their toxin into another animal, whereas a poisonous animal can only deliver their toxin in a more passive manner (by being touched or eaten). A common example given to clarify this difference is that frogs are poisonous while snakes are venomous. It is also important to note that the affects from a venomous fish sting can often be relieved by immersing the wound in hot water (~105–115F) because these toxins are heat labile (meaning they can be destroyed or altered by heat).

1. Pufferfish (some species are also called toadfish) have been given the title ‘Most Poisonous Fish’ and have also been labeled the second most poisonous vertebrate in the world. The toxin responsible for ranking this fish so high in the “danger zone” is called tetrodotoxin. Tetrodotoxin is neurotoxic and inhibits neural transmission leading to weakness, paralysis, and even death at relatively low concentrations (~2mg). This toxin is found in the fish’s liver, ovaries, intestines and skin, leaving muscle tissue with relatively low and somewhat safe levels to eat. However, only highly trained and certified chefs are allowed to prepare this fish for consumption; a common practice in Japan where pufferfish are considered a delicacy.

 Inflated Pufferfish (Source)
Pufferfish (Source)

2. Stonefish have usurped the title of ‘Most Venomous Fish’ in recent years. They often resemble encrusted stones (hence the name), blending into their natural environment with ease. They deliver their venom through a row of spines on their back that can be extended when threatened (or stepped on). Venom is involuntarily expelled when pressure is placed on the fish and the more pressure the more venom. They reside in the Indo-Pacific region and northern Australia. A sting from one of these fish can cause excruciating pain, rapid swelling, tissue death, muscle weakness, temporary paralysis, and in very rare cases death.

Stonefish (Source)
Stonefish (Source)

3. Lionfish were thought to be the most venomous fish until recent years when stonefish stole the title. These conspicuous fish have venomous dorsal, anal, and pelvic spines covered by a loose sheath that moves down and compresses venom glands when the spine punctures tissue. A sting from these fish can cause extreme pain, swelling, and in very severe cases, cardiovascular collapse. Most lionfish naturally reside in the Indo-Pacific but they have become an invasive species in recent years; most notably along the Atlantic coast of the United States where they are having a major impact on Atlantic coral-reef communities. Lionfish were likely introduced along the Atlantic coast through aquarium releases.

Lionfish (Source)

4. Stingrays are one of the most common groups of fish responsible for human envenomations; largely because many rays bury themselves on the seafloor where people unintentionally step on them. Stingray venom is generally cardiotoxic. The Bluespotted (native to the Indo-Pacific) and Southern (native to the southeastern US) stingrays are some of the most venomous of all stingrays. As a form of warning others, the Bluespotted stingray generally displays its bright blue colored spots as a warning to predators of its highly venomous sting.

Bluespotted stingray (Source)

5. Boxfish and trunkfish are closely related to pufferfish. While these fish are not nearly as poisonous as puffers, they do have an impressive way of defending themselves with poison. When threatened or stressed, they excrete a toxin from specialized skin cells into the water, poisoning marine life in their vicinity. The Hawaiian boxfish in particular excretes a toxin called ostracitoxin or pahutoxin that is known to breakdown or destroy red blood cells.

Boxfish (Source)

Some other venomous fish to check out are other scorpionfish (besides the stonefish and lionfish mentioned above), stargazers, which have two venomous spines in addition to organs near their eyes that cause electric shocks, and striped eel catfish.

Stargazer (Source)

If you know of any other venomous or poisonous fish not mentioned here or have experience with a species listed here please share your knowledge and experience below.

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Auerbach PS. 2007. Marine envenomations. Adapted from the 5th edition of the textbook wilderness Medicine by Mosby-Elsevier.

Barss P. 1984. Wound necrosis caused by the venom of stingrays: pathological findings and surgical management. Med J Australia. 141: 854-855.

Boylan DB, Scheuer PJ. 1967. Pahutoxin: a fish poison. Science. 155:52-56.stingrays

Diaz JH. 2008. The evaluation, management, and prevention of stringray injuries in travelers.

Fenner PJ. 1998. Dangers in the Ocean: the traveler and marine envenomation. II. Marine Vertebrates. J Travel Med. 5:213-216.

Gwee MCE, Gopalakrishnakone P, Yuen R, Khoo HE, Low KSY. 1994. A review of stonefish venoms and toxins. Pharmacology and Therapeutics. 64:509-528.

Vetrano SJ, Lebowitz JB, Marcus S. 2002. Lionfish envenomation. The Journal of Emergency Medicine. 23:379-382.

Yang CC, Liao SC, Deng JF. 1996. Tetrodotoxin poisoning in Taiwan: an analysis of poison center data. Vet Hum Toxicol 38:282-286


  1. Great article! There are a few freshwater catfish species (the Madtoms) that have low levels of anti-predatory venom delivered via pectoral spines.

  2. In the Southern California waters I've had run-ins with Sculpin. Those guys have dorsal spines with venom. A friend of mine some how had one of those spines jab him under the big toe nail. Yeah, it hurt.
    We got him in the truck and drove up the 405 to UCLA Med Center. His toe was very swollen and multi-colored. He told me it felt like molten lead was injected under his nail. After several hours we took him home and bar-b-q'd that Sculpin fish and made really delicious tacos.


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