As a rule, you should not touch marine wildlife. But you especially should not touch marine wildlife that can kill you.

Our ocean is full of toxic creatures, from the blue-ringed octopus to the lionfish, but the stonefish holds the title of most venomous fish in the sea. The name “stonefish” refers to one of several fish in the genus Synanceia within the family Synanceiidae. If we take one further taxonomic step backwards, they are in the order Scorpaeniformes, which includes some other well-known ocean residents, like lionfish, lumpsuckers and sculpins.

Stonefish are found in rocky or muddy bottoms of marine habitats in the Indo-Pacific region. They have excellent camouflage—their bodies are typically brown with orange, yellow or red patches and are textured to resemble the surrounding rocks or coral. You could swim right by a stonefish and never know it was there! Stonefish use this to their advantage while hunting, and will wait for fish to swim by then swiftly attack and swallow their prey.

Now, you might be thinking … ”I don’t love the idea of being next to the most venomous fish in the world and not know it.” And you’re right! You definitely don’t want to be surprised by this guy. The good news is that stonefish use their spines defensively, NOT offensively, so the fish won’t go out of its way to attack you.

If you step on the fish however, it’s a different story. Stonefish have 13 spines lining its back that release venom under pressure. If you inadvertently step on a stonefish thinking it’s a harmless rock, it will pop up its dorsal spines and release venom from two sacs at the base of each spine. Unsurprisingly, the more venom that is injected, the worse it is for you. Stings result in terrible pain, swelling, necrosis (tissue death) and even death. One victim wrote online (which was later reported by ABC News) that after being stung on the finger, it was like “having each knuckle, then the wrist, elbow and shoulder being hit in turn with a sledgehammer over the course of about an hour.”

The good news is there have been very few deaths (that we know of). However, stings require immediate medical attention. This involves heat immersion, which helps denature the venom, and injection of anti-venom. But the best bet is to avoid stings in the first place! If you’re in an area that could be home to stonefish, make sure to:

1. Wear water shoes
2. Always look where you walk
3. Shuffle your feet along the bottom to avoid stepping directly on the fish. This shuffle also helps scare away stingrays, which you don’t want to step on either.

Want to learn more about toxic ocean critters? Read about the difference between venomous and poisonous animals.