New research into the venom in stonefish – the world’s most venomous fish – may lead to better treatments for beachgoers who are stung when they unwittingly step on them. Though reef stonefish don’t look like heartstoppers, their venom is potent enough to cause cardiac arrest and paralyse other muscles, scientists at the University of Queensland and Ghent University in Belgium have found. Resembling encrusted rocks in appearance, stonefish are commonly found in shallow coastal waters of the Indo-Pacific. Bryan Fry, an associate professor at UQ, said stonefish were unique among the venomous fish in having well-defined venom glands that sit at the base of their thirteen dorsal spines. “When you step on it, that presses on the gland, the gland ruptures and the venom squirts up along the spine,” he said. The result is an excruciatingly painful sting that has been described as “worse than childbirth”. Previously, scientists had not been able to determine definitively whether stonefish venom has a paralytic effect in people, despite anecdotal reports after stings. The study, published in the journal Toxicology Letters, confirmed that this was the case. It found the paralytic effects of stonefish venom are inadvertently neutralised when the venom is freeze-dried into a powder form, which occurs regularly for ease of handling and transportation. “It’s an incredibly unstable venom,” said Fry. As a result, he said, antivenom currently developed against stonefish venom may not be entirely effective. “If you’re using a partially degraded venom [to make antivenom], then any antibodies formed won’t be against that intact toxin,” he said. Testing both freeze-dried and freshly milked stonefish venom on artificial neurons, the researchers found that the freeze-drying process only seemed to affect the paralytic properties of the venom, but had no impact on its toxicity to cardiac cells – meaning that existing antivenom works sufficiently to protect against stonefish venom’s potentially lethal effects. Because stonefish venom is heat-sensitive, it breaks down at higher temperatures and pouring warm water on a sting can provide relief. “Hot water will only work against the venom that is still reachable,” Fry said. Antivenom is still required when the venom has already entered into wider circulation in the body. The researchers found the stonefish venom’s paralytic effect resembled a milder version of the venom of death adders. The effect likely evolved as a defence mechanism against predation, Fry said. “When we tested against artificial versions of the nerves from sharks, it’s much more potent against them than it is on humans,” he said. “The paralytic aspect isn’t a major part of the clinical features for humans, which is good.” The venom also hinders the ability of the blood to clot. The findings of the study may also have implications for antivenom against box jellyfish and other venomous marine animals, Fry said.