Stonefish are capable of sloughing their keratinised epidermal layer. This keratin layer accumulates algae and other fouling organisms, which grow on the stonefish's scaleless skin. Reef Stonefish (Synanceia verrucosa) only partially discard this keratin layer, so several layers accumulate over time and form a thick brown layer.
Algae and other fouling organisms invade the discarded keratinised epidermal layers' accumulation, contributing to the almost perfect camouflage and warty appearance of this venomous ambush predator. When the stack of incompletely moulded layers becomes too thick, the animal sloughs all these accumulated crusts entirely to remain protected by its original skin.
When this happens, the Stonefish will appear more bright orange with a red hue, the true colour of its skin (the little orange spots on the stonefish in this underwater video clip are patches where the keratin layer hasn't covered the animal's original skin). At this time, the stonefish will stop all its feeding activities until a new coating grows on its skin and its camouflage and warty appearance has reappeared.
This form of camouflage, where the stonefish tries to resemble something else, in this case, a rock or stone with some algae overgrowth, is called mimesis (from the ancient Greek "mímēsis," meaning imitation). Their disguise serves as a way to hide from stonefish predators such as sharks, stingrays, and moray eels and as a way to ambush their prey, which consists mainly of small fish and crustaceans like shrimp.
Stonefish are probably the world's most venomous fish. Their dorsal spines are no more than a row of hidden epidermal needles supplied by venom glands. These spines become erect when the fish is disturbed. When pressure is applied, the fish injects its venom into the attacker. Stonefish venom is an unstable protein that produces intense vasoconstriction, tending to localise itself around the injected area. Stonefish injuries are said to be excruciatingly painful and require the use of anti-venom to reduce the likelihood of medical complications like the appearance of an oedema (swelling of affected tissues due to fluid buildup) or even death for the unlucky victim.
These venomous spines, however, are not used for hunting prey. They are purely a defensive mechanism for the stonefish against its possible predators.
The stonefish is a non-aggressive fish that can easily be approached by scuba divers. As stone tend not to flee, they must be perfectly aware of their more than excellent camouflage abilities.
I often like to start by showing the zoomed-in details of my subject so that viewers initially don't realise what they are looking at, only to reveal the bigger picture at the end to create that "ooh! Wow, now I see it" effect.
These fish make a great subject for underwater videographers and photographers alike. Underwater footage of stonefish and stonefish relatives, both in video clips and photos, is always popular due to the fact that most observers are intrigued by these fish's appearances, camouflage abilities, and venomous reputation.
Stonefish are also easy to film as they sit most of the time motionless on the reef. The hardest part in underwater stonefish videography and photography is spotting this very cryptic animal.
For another in-depth description about the Reef Stonefish please go to our vlog post 175 or click on this link: https://www.beyondscuba.com/post/a-reef-stonefish-synanceia-verrucosa-reveals-it-selves-by-moving
and vlog post 72 or click on https://www.beyondscuba.com/post/utile-dulci-strategy
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