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Fish Poisoning and Envenomations

Human encounters with venomous marine creatures are common and may result in serious poisoning.

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 not known to be endemic to the United States may still be a medical problem in our area as they may be found at a local science museum or exotic aquarium ( e.g., box jellyfish).

Some marine creatures have a verterbrae (backbone) and some do not (invertebrates).

Invertebrates


This category include many different species of jellyfish.

  • It has been reported that 500,000 jellyfish envenomations occur in the Chesapeake Bay area and 200,000 along the Florida coast every year.
  • Jellyfish stings usually occur when humans are swimming or wading in ocean waters and accidentally come into direct contact with the tentacles of these marine creatures.
  • The tentacles are covered with many specialized stinging cells called nematocytes. These nematocytes release a toxin into the victim.
  • In most cases, these nematocytes only cause injury to the part of skin that comes into direct contact with the tentacles.
  • Detached tentacles found on the beach pose a hazard to humans because they remain capable of envenomation for several weeks (see photo called Jellyfish on the beach)
  • Reactions to exposure to jellyfish tentacles are often instantaneous, but can be delayed.
  • Reactions usually consist of burning, redness, itching and swelling.
  • Sometimes, an allergic reaction can occur in response to the initial sting, which can lead to swelling and further inflammation of the skin.
  • Rarely, an itchy rash can occur in the area that was covered by the bathing suit. This type of poisoning is thought to be caused by the eggs of certain jellyfish and may appear up to 24 hours later.
  • Rarely, severe jellyfish stings can cause weakness, headaches, vomiting, muscle spasms and difficulty with breathing.

There are nearly 9,000 species of jellyfish, which can be broken down into 4 main classes:

  1. Hydrozoa (Portuguese man-of-war)The Portuguese man-of-war lives in the Atlantic Ocean along the East Coast of North America, as well as in the Pacific and Indian oceans.The tentacles of these enormous animals can reach up to 100 feet in length (see photo called Portuguese man-of-war).
  2. Scyphozoa (true jellyfish; most common)Specific types of jellyfish include sea nettles (see photo called jellyfish; sea nettle), lion’s mane (see photo called jellyfish; lion’s mane) and cannonball  (see photo called jellyfish; cannonball or cabbage head).As a rule, the sting of the jellyfish found along the coasts of the United States are considerably less toxic than the hydrozoans and are usually limited to eruptions of the skin where contact took place.
  3. Cubozoa (box jellyfish; most toxic)These animals are found only in the waters of the Indo-Pacific (see photo called box jellyfish)
  4. Anthozoa (sea anemones)Sea anemones are also related to jellyfish but are usually minimally poisonous to humans (see photo called sea anemones).No deaths have been reported as a result of a sting from a sea anemone or coral.

Treatment for Jellyfish Stings

For most stings by the invertebrates the treatment is the same:

  1. Rinse the area involved with seawater (freshwater may cause additional firing of nematocysts).
  2. Do not rub the wound as that can also cause additional firing of nematocysts.
  3. The area should be soaked for at least 30 seconds in 5% acetic acid (vinegar) to inactivate any unfired nematocysts.
  4. Any tentacles should be removed using a gloved or towel-covered hand, or with sand or baking soda paste and gentle scraping with a credit card or other blunt straight-edged tool.
  5. Cold pack compresses at the sting site for 5-10 minutes relieve all but the most severe site pain.  Avoid direct application of ice to the area.
  6. Avoid hot compresses.
  7. Use pain medications such as acetaminophen (Tylenol) or ibuprofen (Advil, Motrin) as needed.
  8. Keep whatever part of the body was stung as still as possible to prevent further spread of the venom.
  9. Itching is usually treated with an antihistamine, such as diphenhydramine (Benadryl).
  10. The doctor may give your child oral steroids (Orapred or prednisone) if their reaction is severe.
  11. Your child may be given a tetanus booster if needed.
  12. When dry, a topical corticosteroid may be applied for several days to treat the skin inflammation.
  13. Do not forget you can call your regional poison control center for advice (1-800-222-1222).
  • Anytime your child has continued or worsening swelling, difficulty breathing or swallowing, or severe pain.
  • Any exposure to the eyes, face, mouth, or genitals also requires urgent evaluation by a physician.

Vertebrates

Fish reported to sting humans include stingrays and a variety of venomous spiny fish including the lionfish, scorpionfish, stonefish and marine catfish.

  • Stingrays are commonly found in tropical, subtropical, and warm temperate oceans.
  • Eleven species are found in U.S. coastal waters.
  • 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.
  • Venoms from these fish can retain full potency for at least 24 to 48 hours after the death of the fish.
  • The venom can be destroyed by heating; therefore, the primary method of treatment is soaking the affected extremity in hot water for 30-90 minutes.

Stingrays

  • In America, stingrays probably sting humans more frequently than any other fish.
  • Just this past September, 2006, Steve Irwin, the hugely popular Australian television personality and conservationist known as the ”Crocodile Hunter”,  was killed by a stingray while filming off the Great Barrier Reef.
  • The three most common stingrays are the round stingray found along the Pacific coast from California to Panama (see photo called Stingray; Round); the blunt-nosed stingray, found along the eastern Atlantic coast of North, Central, and South America and the spotted eagle ray, found throughout the tropical waters from the Atlantic to the Pacific (see photo called Stingray; spotted eagle).
  • Stingray envenomations typically occur when a person steps on a stingray resting on the sea floor. The stingray reflexively whips its tail upward and extends the stinger. This usually produces a laceration or puncture-wound in the foot or leg of the victim.
  • The stinger is covered by a cartilaginous sheath that breaks apart and releases venom as it penetrates the skin of the victim.
  • The sting results in immediate intense pain which peaks after 30-60 minutes and may last up to 48 hours.
  • The stingray venom can cause heart problems such as low blood pressure and arrhythmias.
  • It can also cause sweating, nausea, vomiting, headache, weakness, muscle cramps and abdominal pain.
  • 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.
  • Anti-tetanus agents and antibiotic coverage is usually required because these wounds are prone to infection.

Scorpionfish

  • Scorpionfish include the sculpin commonly found along the California coast (see photo called Scorpionfish).
  • Envenomations are most likely to occur after a fish is caught and is handled improperly, or a swimmer touches or steps on one hiding among the rocks.
  • Envenomations are moderate to severe, but are rarely lethal.
  • Stings are immediately painful, peaking in 60 to 90 minutes if not treated. Pain typically persists for 6 to 12 hours, but may persist for days.
  • Other complications may include weakness, dizziness, swelling and respiratory distress.

Lionfish

  • Lionfish are the least venomous of all the spiny fish and are commonly kept in saltwater
    aquariums (see photo called Lionfish).
  • They account for most of the calls to US poison centers for spiny fish envenomations.
  • They are capable of inflicting painful, but relatively mild wounds.
  • Most injuries resolve on there own and can be treated at home.

Stonefish

  • Stonefish are among the most venomous fish in the world. Over 60
    fatalities have been reported in Australia.
  • Stonefish venom has been compared to cobra venom in potency. It can paralyze the muscles of the body.
  • Stonefish are found in the Indo-Pacific region and not in U.S. coastal waters (see photo called Stonefish).
  • Stonefish antivenin is produced and distributed in the Indo-Pacific regions. In the U.S., clinicians can locate antivenin with the help of a regional poison control center.
  • Wound healing can be delayed up to several months in some cases. Numbness may persist for weeks.

Treatment for spiny fish envenomations

  1. Wounds should be irrigated with the available water (seawater in many cases) to remove debris and
    venom.
  2. The affected area should then be soaked in hot water for 30-90 minutes to reduce pain and inactivate the venom.
  3. The injured person may have difficulty judging the temperature of the water, so care must be taken not to scald the skin.
  4. All patients should receive the appropriate anti-tetanus agent if needed.
  5. X-rays of the affected area may be needed to identify any retained portions of the fish.
  6. In the ER, fragments of spine and other debris may need to be removed.
  7. Large wounds may require suturing.
  8. Infected wounds are treated with antibiotics.

How can fish poisoning and envenomations be prevented?

  • 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 (e.g., seawater for jellyfish stings; warm water for spiny fish stings) at the time of envenomation can provide initial pain relief and prevention of further envenomation.