Stonefish include several species of venomous fish belonging to the large Scorpaenidae family. Members of the Scorpaenidae family can be divided into 3 groups based on their venom organs and toxicity: lionfish (Pterois), scorpionfish (Scorpaena), and stonefish (Syanceja). Scorpaenidae stings are progressively more severe from lionfish to scorpionfish to stonefish. Lionfish typically have long, relatively slender spines with the smallest venom glands and produce the weakest venom. Scorpionfish have shorter but sturdier spines and larger venom glands and, thus, have the potential to deliver a more potent sting. The stonefish have the shortest and strongest spines, the largest venom glands, and can deliver a much larger dose of far more powerful venom to a victim. Each spine is covered with a loose integumentary sheath. During envenomation, the sheath is pushed down the spine causing compression of the venom glands located at the base of the spines. Venom then travels through grooves in the spines and into the wound.

The stonefish is probably the most venomous fish known. They live in shallow waters and are so well camouflaged both in shape and color, that they look like a rock. Sometimes they burrow in the sand and mud and remain there, motionless, for hours. Stonefish grow up to 50 cm (18 inches) long. They have 13 spines on their back, which become erect when the fish is disturbed. Each spine contains 5-10 mg of venom. Stonefish inhabit the tropical waters of Indo-Pacific region. There are no stonefish in the waters around the United States.

Stonefish venom is toxic to muscles and can cause paralysis of cardiac, involuntary, and skeletal muscles.

Stonefish envenomation typically occurs when an unsuspecting swimmer steps on the fish. Severe, sharp local pain is the predominant symptom, and the pain may radiate throughout the affected limb. The pain is excruciating and may come in waves. The pain can be so severe that a person can become delirious or unconscious, and if still in the water, the person may drown. If untreated, the pain worsens over the next 1-2 hours and typically persists for 6-12 hours, though an ache can last for weeks. Paralysis of the surrounding muscles may immobilize the limb, as may pain. Twitching and jerking of the limb is sometimes seen. The pain typically spreads to the lymph nodes. Subsequent erythema, edema, and warmth may involve the affected limb. The wound area is initially ischemic and then cyanotic. Vesicles may form followed by tissue sloughing with surrounding cellulitis. Necrotic ulceration may occur. The intensity of the sting depends on the size of the fish, the number of spines penetrating the skin, and other factors, such as body weight and health of the victim.

Stonefish envenomation can cause heart failure, hypotension, syncope, pulmonary edema, and paralysis of the chest muscles. Bradycardia, irregular heart rate, or asystole are common dysrhythmias. Delirium, incoordination, paralysis, and seizures may occur. Stonefish venom can kill a human within 6-8 hours.

Late complications include paresthesias, secondary infection, ulceration, granuloma formation, or fibrous soft tissue defects.