There are more than 250 species of venomous fish, consisting mostly of shallow water reef or inshore fish. Stingrays are the most commonly encountered venomous fish, with more than 2000 stings reported annually. Eleven species of stingrays are found in US coastal waters.
On the West Coast, the round stingray (Urolophus halleri) is most commonly found; on the east coast and Caribbean, the southern stingray (Dasyatis americana) is most frequently encountered. They are flat, round-bodied fishes that burrow underneath the sand in shallow waters (Fig. 135-5 A and B). When startled or stepped on, the stingray thrusts its spiny tail upward and forward, driving its venom-laden stinging apparatus into the foot or lower extremity of the victim.
A. Stingray. B. Stingray in shallow waters. (Used with permission of Eric Goldenberg, MD)
Varieties of scorpion fish include zebrafish and lionfish (Pterois), scorpion fish (Scorpaena), and stonefish (Synanceja), in increasing order of venom toxicity. Although more common in tropical waters of the Indo-Pacific, these fish are found in the shallow water reefs of the Florida Keys, Gulf of Mexico, southern California, and Hawaii. Lionfish are increasingly popular as aquarium pets (Fig. 135-6).25,26
Catfish are found in both fresh and salt water. Stings occur from spines contained within an integumentary sheath on their dorsal or pectoral fins. The hands and forearms of fishermen and seafood handlers are the most common sting sites.
Stingrays have one to four venomous spines or barbs on the dorsum of a whip-like tail. The spines are retroserrated, so they anchor and may become difficult to remove (Fig. 135-7). As the sting is withdrawn, the sheath surrounding it ruptures and the venom is released. Parts of the sheath may be torn away and remain in the wound. The venom is intensely active, partially heat-labile, and causes varying degrees of local tissue necrosis and cardiovascular disturbances. One death of a 12-year-old male is described in the literature from a stingray spine that directly penetrated the child's chest wall, heart, and lung, resulting in myocardial necrosis and tamponade.27
Scorpion fish have venomous spines on the dorsal, anal, and pelvic fins. This venom is also partially heat-labile. Stonefish have 13 dorsal spines harboring one of the most toxic fish venoms (Fig. 135-8).28 Analysis of stonefish venom reveals several toxic components including hyaluronidase, substances with hemolytic activity, and biogenic amines, such as norepinephrine. Cardiotoxicity is primarily from verrucotoxin, a negative chronotropic and ionotropic agent that acts by inhibiting calcium channels.2
Stonefish. (Reproduced with permission from Brenneke F, Hatz C. Stonefish envenomation—a lucky outcome, Travel Med Infect Dis. 2006; 4(5):281–285.)
For catfish spine stings, heat-labile venoms comprise dermatonecrotic, vasoconstrictive, and other bioactive agents produce symptoms similar to those of mild stingray envenomations. A unique parasitic catfish, the Amazonian Candiru (genus Urinophilus), may invade its victim by swimming “upstream” into the human urethra. Acute painful hemorrhage may result if forceful extraction of the catfish is attempted.29
With stingrays, intense pain out of proportion to the apparent injury is the initial finding, peaking within 1 hour and lasting up to 48 hours. Signs and symptoms are usually limited to the injured area, but weakness, nausea, anxiety, and syncope have been reported.
Envenomations from lionfish, scorpion fish, and stonefish cause immediate intense pain that peaks within 60–90 minutes and persists for up to 12 hours. Local erythema or blanching, edema, and paresthesias may persist for weeks. Systemic findings include nausea and vomiting, weakness, dizziness, and respiratory distress. Although similar to those of the other scorpion fish, stonefish stings are more severe. Stonefish venom, a potent neurotoxin, can cause dyspnea, hypotension, and cardiovascular collapse within 1 hour and death within 6 hours. Local necrosis and severe pain may persist for days.
With catfish stings, burning and throbbing sensation occurs immediately but usually resolves within 60–90 minutes. The discomfort may last up to 48 hours. Systemic symptoms are rarely reported.
Treatment of stingray wounds includes irrigation with sterile saline to dilute the venom and remove sheath fragments. The spine of the stingray including the venom gland is typically difficult to remove from the victim and radiographs may be necessary to locate the spine or retained fragments.30 However, a recent large retrospective study of 119 stingray injuries found no positive radiographic evidence of foreign bodies in any of their patients.31
The injured part should be immersed in hot water, no warmer than 113ºF, for 30–90 minutes, to inactivate any heat-labile venom components.23 Analgesics are usually required. Because of the penetrating nature of the envenomation, wounds should be debrided and left open. Tetanus immunization is updated if needed. Treatment with a broad-spectrum prophylactic antibiotic such as trimethoprim–sulfamethoxazole (TMP–SMX), ciprofloxacin, or a third-generation cephalosporin is recommended because of concern for infection by Vibrio species, as well as Staphylococcus and Streptococcus spp.32
Treatment for scorpion fish and lionfish envenomation is immersion of the affected limb in hot water (113ºF) for 30–90 minutes, or until pain is relieved. Some case reports have documented failure to respond to standard warm water immersion therapy at 45ºC.26 Wounds should be irrigated with sterile saline, explored, and cleaned of debris. The wound is left open and treatment with prophylactic antibiotics is initiated.33 Local treatment for a stonefish sting is the same as that for envenomations by other scorpion fish, with special attention given to maintaining cardiovascular support.6 One recent report describes a case of foot stonefish envenomation treated by vacuum-assisted closure therapy as an easy to use, accessible, and simple adjuvant tool for management of large soft tissue necrosis.33
There is a specific stonefish antivenom available in Australia.2,35 The antivenom is an equine-derived product and carries the risk for inducing anaphylaxis. One 2 mL ampule of stonefish antivenom is diluted in 50 mL normal saline and given IVPB. A case series of eight patients suggests that the majority of stonefish envenomations do not result in significant morbidity or mortality and usually require only supportive management.36 Another larger more recent series of 57 patients suffering stonefish envenomation noted severe pain in 95% of victims with half of the patients requiring hospital admission. All responded to analgesic medications and antibiotic coverage and there was no mention of antivenom administration.37 It remains uncertain whether stonefish antivenom is efficacious in stings of other venomous fish.18
Catfish sting treatment is immediate immersion in hot water (no warmer than 113ºF) for pain relief. Catfish spines may penetrate the skin and break off. Sometimes, the spines can be located by routine radiographs. Occasionally, MRI is necessary to locate a foreign body. The wound should be explored and debrided. Retained catfish spines should be removed by a qualified practitioner. The puncture wound is left open. Treatment with prophylactic, broad-spectrum antibiotics and tetanus prophylaxis are indicated.
Children with mild stings responsive to hot water soaks may be discharged after observation. Children not responsive to pain management may have a retained foreign body. Children envenomed by stonefish should be monitored in an intensive care setting. If it is available, antivenom administration is indicated in symptomatic patients.