Stonefish are masters of disguise, as they can look like a harmless rock or stone lying on the seabed. But the failure to distinguish a stonefish from a stone due to this camouflaging can have life-threatening consequences at times. Stonefish are the most venomous fish currently known in the world. So, this fish can inflict a fatal and excruciatingly painful sting, if someone inadvertently steps on it. However, stonefish are not aggressive and do not attack unless they are provoked or when someone accidentally steps on them. They belong to the genus Synanceia, and the family Synanceiidae. Members of the genus Synanceia, including scorpionfish, are sometimes placed in the Scorpaenidae family. The most commonly found species of stonefish are Synanceia verrucosa, also known as 'reef stonefish' and Synanceia horrida or 'estuarine stonefish'. True to their name, stonefish look like crusted rocks or rubble lying on the seabed. But if you look closely, you can notice some interesting features, which are discussed below. ✦ Most stonefish are brown or gray with yellow, orange, or red patches on their body. The estuarine stonefish is usually brown or reddish-brown in color. The orange, sponge-like growths found in some stonefish can make them look like a piece of rubble in the coral reef. ✦ The reef stonefish usually reaches a size of 35 cm, though some can grow to a size of 50 cm. So far the largest specimen to be recorded was 51 cm in length. Stonefish can weigh about 2,400 gms. ✦ Stonefish possess huge bug-like eyes, and the placement of the eyes can help distinguish a reef stonefish from an estuarine stonefish. The eyes of the estuarine stonefish are more elevated than reef stonefish, and they are separated by a bony ridge. On the other hand, the eyes of the reef stonefish are set apart by a deep depression. ✦ One of the most important features of a stonefish is its needle-like modified dorsal fin, at the base of which the pressure-sensitive venom glands are located. Stonefish possess 13 sharp dorsal fin spines, and whenever the fish feels threatened it raises them to defend itself. ✦ Along with the 13 dorsal fin spines, a stonefish possesses two pelvic and three anal spines, but they remain buried within the skin. ✦ The stonefish does not have scales. The encrusted skin of this fish gives it the appearance of a rough stone. Stonefish are mainly found in the coastal regions of Indo-Pacific oceans and the waters of northern Australia. Their main habitat are coral reefs. However, they can also be found near and under rock ledges, and mud or sand in tidal inlets. Though stonefish are largely marine fish, some of them can dwell in rivers as well. ✦ Both reef stonefish and estuarine stonefish exhibit the same pattern of reproduction. The female of the species carries within itself the unfertilized eggs, which are released on the sea floor, or a rock shelf. ✦ When a male stonefish reaches that area, it sprays sperms over the eggs. The fertilized eggs then hatch within three days. The newborn stonefish fall prey to other fish, and so, out of millions of baby stonefish only a few survive to reach adulthood. ✦ The stonefish is a bottom-dweller, that mainly feeds on small fish and shrimp. ✦ The stonefish is a patient hunter that waits in disguise for hours until a prey comes within its striking range. Sometimes, it buries itself in the sand or under the ledges in such a way that only the top of its head and the spines remain exposed. If a prey is positioned behind its head, a stonefish raises its needle-like dorsal fin spines to scare the prey and bring it into the striking zone. ✦ When a prey is within its striking zone, a stonefish thrusts its jaw forward in the upward direction and then expands its mouth cavity at lightening speed to gulp down the prey. The entire process takes only 0.015 seconds. ✦ Stonefish themselves fall prey to bottom-feeding sharks and rays. When stonefish encounter these predators, they try to defend themselves with their poisonous spines. ✦ The venom glands located at the base of these spines contain neurotoxins. The toxins found in stonefish include haemolytic stonustoxin, protinaceous verrucotoxin, and cardioactive cardioleputin. These toxins are primarily made of protein and are involuntarily expelled through the dorsal fin spines when pressure is applied on them. ✦ After injecting the venom, the glands need a few weeks to get refilled. It has been found that the amount of venom discharged by these glands is proportional to the extent of pressure applied on them. ✦ Stonefish are consumed in China, Hong Kong, and Japan. In Japan, it is served as a 'sashimi' cuisine, called 'okoze'. ✦ The stonefish can spit water, which is quite unusual for a fish. ✦ As stonefish are venomous, their sting can produce severe pain and swelling. It can eventually cause tissue death and paralysis, depending on the depth of penetration and the number of spines penetrated. ✦ To educate their children about the dangers of reef stonefish, the Australian aborigines used to perform a dance. They used to place a clay model of stonefish in water. A performer then walked through the water and stepped on the clay model, and screamed in terrible agony. Despite being venomous, stonefish are largely sold as aquarium pets. Usually, individuals stung by stonefish are advised to seek medical attention, as anti-venom can be required to prevent any life-threatening complication. Application of heat on the wound can help lessen the effects of the toxin and reduce the pain. However, the practice of tying a cloth on the wound to restrict the movement of venom is not recommended in this case. To avoid a dangerous encounter with stonefish, it is better to tread gently on beaches and wear thick-soled footwear. By stepping very lightly in water and avoiding anything that looks like a rock, swimmers can avoid an accidental encounter with stonefish.