The Reef stonefish is the most venomous fish in the world. It is a master of disguise. It can camouflage itself and blend effortlessly into its environment to appear like a piece of coral or an encrusted rock.
Living around the coast of Australia especially in the Great Barrier Reef, it has thirteen sturdy spines along its dorsal fin that can inject a highly toxic and intensely painful venom into anyone who attacks it.
The stonefish is a carnivorous bottom dwelling fish that usually hides amongst coral and rocks. It is a rather stout fish about 35cm – 50cm in length. The stonefish has a large upward-opening mouth. It does not have scales. Its skin is covered with bumps and nodules and may have filaments and growths that appear like outgrowths of algae. The key difference between males and females is size. The female stonefish is larger and broader around the abdomen than the male and can weigh as much as 50% more.
The base colour of a stonefish is usually grey or brown with patches of yellow, orange and red. Its favourite disguise is that of a rock – hence its name of stonefish. The stonefish has the uncanny ability to morph into various rock-like shapes and to add splashes of colour to its appearance to mimic and blend in with its surroundings. Even its eyes can impersonate algae. Typically it tries to appear like an algae encrusted rock or coral. Is also lays on soft sand or mud and, using its large pectoral fins as spades, it partially buries itself to appear like a rock on the sea-floor. Hidden by its excellent disguise it waits motionless for prey to pass by.
Stone Fish and Scorpionfish are often confused.
The stonefish is best at pretending to be a stone and is capable of less colour-matching compared to the scorpionfish. It is also the most venomous fish in the world. Only its dorsal fin is venomous.
The scorpionfish on the other hand, has more prominent eyes and can change its colour to better match its surroundings including colourful corals. It has venomous spines on its back as well as on its fins. It isn't as venomous as the stonefish.
World-wide there are five species of stonefish. They all share common characteristics. Two species of stonefish are found in waters around Australia and are the most venomous. The only way to tell them apart is in the position of their eyes. The Reef Stone Fish (Synanceia verrucosa) has a deep depression between its eyes. The Estuary Stone Fish (Synanceia horrida) has elevated eyes separated by a bony ridge.
From a human perspective it is the stonefish's dorsal fin (the top fin on its back) that draws the most attention. The dorsal fin of the stonefish is supported by 13 fully covered spines. But unlike most fish these hidden spines are hollow and connected to venom glands that discharge their contents along ducts in each spine. Usually these sharp hypodermic needle-like spines are hidden beneath the skin of its dorsal fin. However, if the animal's spine or dorsal fin were to be squeezed these needle-like spines break through its skin and impale the attacker, injecting venom into the wound. Its deadly spines are strictly defensive. It never uses them to capture or attack other animals.
The stonefish can survive out of water for up to 24 hours. This may be an adaptation to its shallow water existence where it may get trapped in drying out rock-pools during low tide.
The Stone Fish is a bottom dwelling fish found in shallow coastal waters where it usually hides amongst coral or rock formations and camouflages itself by adapting the characteristics of its environment. It may pretend to look like a clump of coral or a piece of rock. Where there isn't sufficient cover, it will use its powerful pectoral fins it dig itself into the seabed and pretend to be something most appropriate to its surroundings, typically an algae covered rock.
The stonefish is a carnivore. It eats other reef fish and bottom dwelling invertebrates. The stonefish is a sit-and-wait ambush predator. It stays motionless in one position grabs its prey when they swim close by.
The stonefish's capture technique is called ‘gape and suck’. The stonefish can expand the volume of its throat, which has extra pleated skin to allow expansion, and mouth in a split second. When it opens its powerful jaws wide open and expands its throat, it creates a significant vacuum suction pressure between the inside of its mouth and the outside environment which sucks its unsuspecting prey into its gaping mouth where it is swallowed whole. This action is so quick that it's all over in less than 1/100th of a second.
The stonefish is a solitary animal. The old time its actively seeks out another is during mating season for spawning. The female stonefish release a layer of fertilised eggs on the seafloor and the male comes along releasing sperm over them.
The main predators of the stonefish are sharks, stingrays and sea snakes. They are not endangered.
Are stonefish dangerous? Absolutely!
The stonefish is the most venomous fish in the world. Hidden beneath its dorsal fin are 13 spines with deadly spikes that act like hypodermic needles and inject highly toxic venom into any creature that comes in contact with them. The venom in these spines are usually released only when pressure is applied to the stonefish’s spine, which means the venom is most often emitted when the stonefish is being attacked by a predator or stepped on by a human. Stone Fish venom has both cardiovascular and neuromuscular toxicity. The pain caused by the venom is described as being immediate and excruciatingly painful and may last many days. The severity of the outcome is depended on the number of punctures suffered from these spines. Symptoms include muscular paralysis, breathing difficulties and shock. If left untreated heart failure and death may occur.
There have been no recorded human deaths in Australia as a result of an encounter with a stonefish. It is believed that a number of fatalities may occur in other Indo-Pacific areas usually as a consequence of the lack of medical treatment.
Stone Fish antivenom is the second-most frequently administered antivenom in Australia.
Do stonefish attack humans? Absolutely Not!
Stone Fish do not attack humans. Instead, they do what they have always done and stay hidden and motionless in their habitat with their venomous dorsal fin spines erect as a defence. They are also sometimes washed up near the shoreline or on beaches where humans may step on them or pick them up. So strictly speaking any injury suffered by a human is self-inflicted – You ventured into its habitat, stepped on it or touched it. You didn't leave the animal alone.
The stonefish, the most venomous fish in the world, is indeed edible – provided it is prepared properly. The protein-based venom quickly breaks down when cooked. If eaten raw it is safe to eat provided the fish's dorsal fin with its associated venom is removed. It is a delicacy in Japan and China.
The best precaution against a stonefish injury is to be alert and wear sturdy footwear, not to touch or pick these animals up.
Wash the wound with cold water (saltwater is fine). Then apply heat to the wound for 30-90 minutes. Soaking the wound in very hot water (but not so hot that it causes burns on the victim) is one easy option. Heat may help destroy stonefish venom, and provide some pain relief to the victim. Vinegar, provided on most Australian beaches for use against jellyfish stings, is also said to lessen the pain.
These remedies are offer temporary relief only. Medical treatment should always be sought urgently.