Lionfish envenoming

Lionfish (Pterois volitans and related species) are a type of scorpionfish and common cause of fish spine envenoming. Indeed, in the United States where these beautiful fish are widely kept in aquariums, the lionfish is probably the most common cause of fish envenoming.

• Located among the fins of the common lionfish (Pterois volitans) are 13 dorsal, 3 anal, and 2 pelvic spines, each of which has a corresponding pair of venom glands.

Lionfish have many other names, including: Zebrafish, Butterfly Cod, Firecod, Turkeyfish, and Firefish. There are many related species, all sharing a similar banding pattern and long feathery fins. Examples include:

• Devil firefish – Pterois miles
• Japanese lionfish – Pterois lunulata
• Common lionfish – Pterois volitans
• Whitelined lionfish – Pterois radiata
• Russell’s lionfish – Pterois russelli
• African lionfish – Pterois mombasae
• Banded lionfish – Pterois antennata
• Zebra lionfish – Dendrochirus zebra
• Shortfin lionfish – Dendrochirus brachypterus

Geographic distribution and habitat

• As well as being found in aquariums worldwide, lionfish may be encountered in any of the world’s oceans, although most stings occur in the tropical regions of the Mediterranean and the Indo-Pacific region.
• In Australia, various types of lionfish may be found on all but the southern coast of the country (from Cape Leeuwin in Western Australia to central New South Wales). It’s typical habitat is shallow water around rocks and coral reefs.

Envenoming usually occurs in one of two contexts:

• Lionfish are now widely kept in aquariums, sometimes by owners who are not even aware that the animal is venomous. As a result accidental or intentional spine contact with an aquarium fish is a common mechanism of injury.
• In the wild, lionfish may also come into contact with divers as they tend to have inquisitive natures and have a highly attractive appearance.

Clinical presentation:

• The predominant feature is usually severe pain and distress out of proportion to the apparent severity of the injury.
  • A person stung by a lionfish experiences immediate severe pain at the wound site that escalates over a period of minutes and may extend throughout the affected limb (about 1 in 5).
  • Peak pain typically occurs at about 90 minutes. The pain can persist up to days, but typical resolves over a period of 6-12 hours.
• The local effects of the sting may result in:
  • Marked swelling, enlargement and tenderness of the draining lymph nodes.
  • Blistering and dermal necrosis has been reported.
  • Puncture sites that may be visible and spine remnants may be present in the wound.
  • Nonspecific systemic features (about 1 in 7) may include:
    • nausea and vomiting, diaphoresis, difficulty breathing, chest or abdominal pain, generalized weakness, hypotension, and syncope.
  • Deaths have been reported internationally, but not in Australia.

Lionfish venom most closely resembles the venom of Stonefish (Synanceia horrida) in terms of pharmacological activity.

• However, marked muscle weakness has also been noted in experimental animals as has neuromuscular blockade activity.

The venom is injected through a puncture wound created by the spine, which rips the integumentary sheath and may fracture the venom spine.

Prehospital

• Reassure the patient, consider oral analgesia
• Hot water immersion (see Q5)
• Transport all patients with significant pain refractory to first aid and oral analgesia, and those with systemic features, to a medical facility
• Do not apply a tourniquet or pressure immobilization bandage (PIB)

Hospital

• Resuscitation –
  • Lionfish envenoming is highly unlikely to be life-threatening.
• Supportive care and monitoring –
  • Analgesia
    • hot water immersion (see Q5)
    • oral analgesia
    • consider regional anesthesia if refractory to hot water immersion
    • (avoid local adrenaline injections as it may delay microvascular clearance and increase the risk of local necrosis)
    • intravenous analgesia (eg. IV morphine 0.1 mg/kg (up to 5 mg) repeated every 20 minutes until the patient is comfortable
  • Wound management
    • Careful wound examination, removal of foreign material, and irrigation. Extensive debridement is not usually required.
    • Antibiotics are not routinely required.
    • Consider antibiotics to cover marine organisms if delayed irrigation/ deep puncture wounds present (eg. doxycylcine or ciprofloxacin)
    • Tetanus prophylaxis

• Investigations – as required to detect/ confirm local and systemic effects of stingray injury and complications:
  • Wound radiograph or ultrasound (if undetected foreign body suspected)
  • Wound swab (consider if high risk of infection – specify seawater involvement on the request form)
• Decontamination – nil
• Enhance elimination – nil
• Antidotes – nil (Laboratory studies suggest that Stonefish antivenom may neutralize some components of Lionfish venom, but it is unproven and unlikely to be required)
• Disposition –
  • Patients without clinical features of systemic envenoming at 2 hours do not require further medical observation.
  • Patients requiring opioid analgesia may be discharged when they have been asymptomatic for a period of 4 hours.

Hot water immersion is used as treatment of pain resulting from fish envenoming. It should be performed as soon as possible. It appears to be at least partially effective for most venomous fish stings.

• The affected limb should be immersed in hot water (45ºC) for at least 30 minutes (up to about 90 min) or until there is pain relief.
• An unaffected limb should also be immersed to ensure water temperature is tolerable and so prevent burns.
• Extreme caution should be taken in using hot water immersion after a ‘failed’ attempt at regional anesthesia as delayed or partial anesthesia may result in significant burns.

The mechanism of analgesia from hot water immersion is uncertain.

• Many fish venom constituents are thermolabile and it is thought by some that analgesia results from denaturation of these venom components.
• However, removal of the affected body part sometimes results in the rapid escalation of pain. Unless the toxins somehow renature, the thermolability hypothesis does not seem to readily explain this phenomenon.
• Others have suggested that hot water immersion somehow modulates pain neurotransmission in fish spine envenomings.

The scorpionfish are probably second only to stingrays (see Toxicology Conundrum 012) as the culprit in fish spine envenoming globally.

• The defining feature of scorpionfish is the presence of a bony plate or stay that extends from the eye of the fish to the gill cover.
• Scorpionfish consists of hundreds of species that fall into three different groups of genera according to venom organ structure (classification systems vary). The groups also differ in terms of severity of the clinical effect:

1. Pteroinae (zebrafish, lionfish, and butterfly cod) – mild envenoming
2. Scorpaenidae (scorpionfish, bullrout, and sculpin) – moderate envenoming
3. Synanceiidae (stonefish) – severe envenoming

• Atkinson PR, Boyle A, Hartin D, McAuley D. Is hot water immersion an effective treatment for marine envenomation? Emerg Med J. 2006 Jul;23(7):503-8 [pubmed]
• Garyfallou GT, Madden JF. Lionfish Envenomation. AnnEmergMed 1996;28:456-7 [pubmed]
• Kizer KW, McKinney HE, Auerbach PS. Scorpaenidae envenomation: A five-year poison center experience. JAMA 1985;253:807-810. [pubmed]
• Sutherland SK, Tibballs J (2001). Australian animal toxins: the creatures, their toxins and care of the poisoned patient. Melbourne, Oxford University Press.