The Reef Stonefish: The Camo Killer.
Synanceia verrucosa, is also known as the rockfish, the reef stonefish and dornorn; is the most venomous fish in the world. Although, there are other venomous fishes out there, the reef stonefish is the one species which has been studied extensively. Being a master of camouflage, it takes on the realistic appearance of stones and corals, which can have a somewhat life threatening implication for those who fail to distinguish the reef stonefish from rocks on the sea floor. However, despite what many think, the reef stonefish in not an aggressive hunter, but an ambush predator and it only using its lethal venom involuntarily as a defence mechanism.
The reef stonefish is usually found in the shallow water regions of the Indo – Pacific coastal waters. Synanceia verrucosa resides in sandy and rubble areas of reef flats, coral rubble pools and under rock ledges. Generally, this species of stonefish is found at depths of approximately 20m. However, in recent years the reef stonefish has been found in the waters of the Mediterranean Sea. For example; in April 2010 a specimen was found off of the coast of Israel at a depth of 3m. Although there have been recent sightings, there is no apparent evidence to suggest that there is an established population settling in the coastal waters of the Mediterranean Sea.
Appearance Is Everything:
True its name, the reef stonefish’s grotesque appearance resembles that of rocks or coral. Unlike other teleost’s, Synanceia verrucosa does not possess scales, instead they have an encrusted skin, which allows them to disguise themselves and hide in plain sight from predators and potential prey. This remarkable camouflage is taken to a whole new level, as some individuals have fouling organisms, such as the algae growing on their skin. The reef stonefish mimics the appearance of an algal covered stone, with small wart like growths which cover the encrusted skin. These warts are meant to look like strands of filamentous algae, diatoms and other organisms, in order to attract prey. The colour of the reef stonefish varies among individuals, depending on the environment on which they reside. Most
individuals are usually grey to mimic rocks, or tan coloured to resemble sand. Some individuals even have patches of bright red, orange or yellow to increase the chances of blending into the corals. An advantage of an incredible disguise, is that it attracts unsuspecting herbivorous prey into the striking zone. Another adaptation which the reef stonefish possesses, is the ability to slough its skin; meaning it can shed the entirety of its skin in one go. However, this process only occurs once 3 – 4 layers of skin has accumulated over the body, taking on average approximately 4 hours. The newest layer of skin stays attached to the body, whereas the older layers which have been overrun by fouling organisms are discarded.
The Patience of a Saint:
The reef stonefish is an ambush predator, meaning it will not actively hunt down its prey. Referred to as a “lie – in – wait” predator, the stonefish will bury itself into the sand or mud, waiting in plain sight for hours on end until the opportune moment to strike its prey. The process of prey capture for this cryptic fish is categorised into three distinct stages; the first of which is prey orientation, secondly comes seizure of prey by expansion and compression of the mouth, and lastly the manipulation and deglutition of the victim. Synanceia verrucosa will wait patiently until an unlucky prey item swims into close proximity to the mouth, relying on ultrafast and a highly protrusible jaw to capture the prey with an element of surprise. Thrusting its jaw forward and upwards, creating an increase in pressure within the mouth cavity, the reef stonefish ultimately sucks in the prey item. This rapid movement allows the reef stonefish to swallow the entirety of its oblivious prey, in a record time of only 0.015 seconds. Synanceia verrucosa typically has a diet of small to medium sized fish, crustaceans such as shrimp and sometimes cephalopods.
Small but Mighty:
Being the most venomous fish in the world does not mean the reef stonefish avoids predation. Synanceia verrucosa, falls prey to bottom feeding sharks and rays. However the reef stonefish is well prepared for predatory attacks, with its fully loaded defence system. In the big blue, you don’t have to be the largest or strongest to be the most dangerous. The reef stonefish only reaches a mere average length of 35 cm and up to 2 kg in weight. There are many unique features of the reef stonefish, such as their modified dorsal, pectoral and anal fins. The anal and pectoral fins are quite interesting as they remain buried within the skin; the pectoral fins are adapted to help the reef stonefish hop about the seabed and for burying itself into the sand and mud. On the other hand, the dorsal fin is adapted for a very different function; a highly lethal defence mechanism. There are thirteen dorsal spines, which are covered by tubercular sheaths of skin.
Each of the thirteen spines are connected to pressure sensitive twin venom glands, via the venom ducts that are enclosed within grooves running along the length of the spines. The venom glands are stimulated by an external stimuli – meaning when the tip of the spines penetrate an object, the sheath of skin are pushed downwards, away from the spine towards the gland. The tissue around the spines and grooves are densely collagenous fibres, which constrict the glands when enough pressure is applied. The venom then involuntarily shoots out of the glands along the grooves and injected into the wound by the spines. The amount of venom released is directly proportional to the amount of pressure that is applied to the spines. Once the venom has been discharged from the glands, it usually takes up to a few weeks before the glands are refilled.
Synanceia verrucosa has the most complex and evolved venom of all the venomous fish. The venom is made up of many different toxins making it so lethal; it is thought that only 18mg of the venom released by 6 spines, is enough to cause death. The toxins which are found in the venom include; proteinaceous verrucotoxin, cardioactive cardioleputin, haemolytic stonustoxin; all of which have cardio toxic, neurotoxic, myotoxic and vascular leakage effects on the victim. The venom results in an incredibly excruciating painfully slow death upon the victim. As it creates pores within the cell membranes, causing tissue death and paralysis. However, as the venom is made up of mainly proteins, when heat is applied to the affected area, the effects of the venom is lessened and pain is reduced. Although this is not recommended by doctors and professional help is advised immediately for those who fall victim to the harsh sting of the reef stonefish.