These creatures are called stonefish because actually they do resemble a stone, a quite ugly one, by the way. As ugly as only a stone with eyes, mouth, gills, fins and venomous spines could be. Not that the venomous spines make this creature uglier in themselves, it is just their tendency to be quite dangerous (actually deadly), that makes them horrible.

Stonefish are cousins of other scorpionidae, such as the scorpion fish and the lion fish. Apart from the beautiful lion fish (Pterois Volitans), scorpionidae tend to share an equal amount of venomousness and “ugliness”. However, the most dangerous of them is the Synanceia verrucosa, the stonefish.

This species doesn’t swim but moves very slowly, making small jumps, and its preferred habitat is a coral garden with a sandy bottom. The stonefish is known because of its formidable mimetic ability: one can hardly make one out from the background, whether this is a sandy bottom, a coral head or a madreporic formation. Diving guides and photographers need to know their exact location since it is almost impossible for the human eye to distinguish a stonefish from the background where it is resting. Fortunately, this creature tends to move very little. It often stays on the same coral head or sandy slope for weeks, even months. They are able to transform their natural paraphernalia of filaments around their body to the colour of seaweed, in order to closely resemble a piece of dead coral.

They can be spotted only thanks to three important anatomic features: the gills, which move every time the fish breathes; the mouth, similar to a grumpy half moon; the eyes, situated on the top of the forehead. As all scorpenidae, it literally sucks in its victims when they pass by, and their venom is only used in defence, rather than to catch their food.

Like most venomous fish, and some reptiles, the body of the stonefish synthesises a venom based on proteins: this protein is thermolable. This means that a person who has been accidentally hit by a stonefish’ venomous spine, can submerge the body part in water that is at least 60 °C hot. This is a temperature that definitively burns, but better burnt than dead.

The pain of a stonefish’ puncture is so intense that a diver accidentally hit by one could possibly never make it to the surface due to convulsions. Fortunately, the shy nature of the stonefish, its tendency to choose hidden crevices as its home and the fact that it hardly moves, make it very difficult to be hit by a stonefish venomous spine.

This danger, which makes it curiously more attractive to expert divers and photographers, actually reminds us how important is to keep to proper behaviour underwater: perfect buoyancy and, one of the main rules of underwater environment conservation, never touch anything.

An adult stonefish can be from 20 to 40 cm wide. It is quite easy to confuse a stonefish with a devil fish, or false stonefish (Scorpaenopsis Diabolous). These are equally chameleonic, but are different from stonefish in that the mouth is positioned differently and is almost horizontal rather than curved. Also, the devil fish has a smooth head without any of the verrucae that the stonefish presents. The stonefish has the mouth situated at the same level as the rest of the upper section of its body and its head is literally covered with verrucae.

During the mating season, usually the winter months, the stonefish turns a pink or deep red colour, with white patches around its verrucae (the venom glands), in order to be easily spotted by potential partners. This is the only season when it is easier to spot a stonefish underwater, as these colours seldom match those of the background where they are resting.