Fish Stings

Fish stings represent a real risk to holiday makers who are relaxing in the sea, or even in freshwater where the fresh water sting ray can cause problems. Venomous fish generally have bony spines covered by venom-secreting tissues and most individuals are stung when they tread on or touch a fish that possesses a venom apparatus (War-rell, 1983). There are a number of families of venomous species found worldwide in tropical waters. Stingrays have a flat, triangular-shaped body varying in width from a few centimetres to over 5 m. When trodden on they whip their tail forward, which possesses a retroserrate sting. Catfish are mostly riverine, sometimes coastal, fish with serrated spines and whiskery mouthparts. Scorpion-fish (Scorpaenidae) are widely distributed in tropical seas, especially around coral reefs. They have multiple dorsal spines and include Trachinus species (weeverfish), Pterois species (zebrafish, lionfish, tigerfish, etc.) and Synanceja (stonefish) species. Venom is injected by mechanical pressure of the victim's tissue upon the venom gland around a spine.

Avoiding Fish Stings

If swimming or bathing in areas where such fish are known to be present, it is sensible to wear some sort of protective footwear (e.g. 'flip-flops' or plastic lightweight sandals). Care should be exercised when swimming near or touching items on sandy bottoms.

Clinical Features

The main effect of stings by these fish is an intense and often agonising local pain. This is often stated to be the worst pain ever experienced by the victim and may lead to extreme distress and incoherence. Stingray injuries may cause significant lacerations and even deep puncture wounds. Systemic symptoms are generally rare in envenoming by fish, although there are reports of deaths from some areas of the world following stonefish, zebrafish and weeverfish stings. Most species cause rapid swelling and a bluish discoloration around the sting; stonefish do not cause local necrosis, but this may be a prominent feature in weeverfish and catfish stings. Spines may becomes detached and remain embedded, leading to a chronic infection and discharge.

Figure 21.12 Sea wasp or box jellyfish, Chironex fleckeri, the jellyfish most dangerous to humans. In its natural waters it is translucent and very difficult to see. (Photograph courtesy of J. Gillet)

Treatment

The most effective treatment for the local pain of venomous fish stings is hot water, as many marine toxins are heat labile. The part stung is immersed in water as hot as the patient can bear; care must be taken to avoid burning and blistering as the severe pain may alter the sensation of the affected limb. The clinician should check that he or she can bear the water temperature without pain and asking the patient to check the temperature with the other limb is sometimes useful. The pain may be relieved rapidly, but continued immersion and maintenance of the temperature is necessary; this may be achieved by continually adding boiling water to the immersing water to keep it as constantly hot as the patient can bear (with repeated checking by the clinician). Regional nerve block may be helpful and, if the part stung is unsuitable for immersion in hot water (for example, the face or trunk), the area should be infiltrated through the puncture wound with 2-5 ml of 1 % lidocaine (lignocaine) hydrochloride. Stone-fish antivenom is available in Australia (only for intramuscular use) and appears to be very effective in relieving the pain. Stingray injuries may require surgical exploration and debridement.

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