Sunday, September 30, 2001		Nature

SOME seabed dwelling animals are masters of camouflage that makes them almost invisible and gives them chance to surprise unwary passersby. One such example is the deadly stone fish that frequents the seabed and hunts by ambushing its prey. As its name suggests, it looks like week-covered stone or coral and its outline only becomes apparent to the casual observer if its eyes can be picked out first.

Found in warm, shallow waters, some types of stone fish produce mock strands of algae from their own tissue to fool prey and deter predators. Besides being heavily camouflaged these lethargic creatures are also among the most venomous fish. For human swimmers, to step on one of these almost invisible bottom-dwellers is to experience perhaps the worst possible pain. Even the most fiendish human torturer has fallen far short of the agony provided by this small fish. Its only response to being disturbed is to erect its dorsal spines. It makes no attempts to move away, even if the water nearby is being violently disturbed.

In these fishes the venom is held in small sacs near the tips of the spines, so when any human sets a foot on the fish the poison is squeezed into the wound by the downward pressure. The fish does nothing — the victim impales himself. And the ensuing pain is so intense that the victims seem, for a while, to go out of their minds.

They rush from the water, fling themselves down on the beach and proceed to roll around in agony, screaming and frothing at the mouth. Helpers approaching them have sometimes been bitten or attacked wildly in the delirium that follows and which may last as long as 12 tortuous hours. Morphine has no effect. Raving and thrashing about, the victim becomes gradually weaker and, if lucky, may eventually become unconscious. The injured limb swells up until it looks like the leg of an elephant. The toes or fingers nearest to the wound turn black and later drop off. Death is not uncommon, but an anti-venin has now been produced and is effective if it can be used in time.

The stonefish is the most deadly of all fishes, but many others too possess poisonous spines developed from fin-rays. The golden rule is that all prickly-looking fish should be treated with great respect. Others examples include the scorpion fish, lion fish, rabbitfish, toadfish, waspfish, frogfish and many of the catfish. Some, like the stonefish, are inconspicuous, while others flaunt their chemical power by sailing around in bright colours that dare you to touch them. The beautiful lion fish belongs to this gaudy category and is there fore much easier to avoid. All these spikes evolved originally as a way of preventing predation by larger fish. Today, with powerful venoms added, they have become a formidable defence system against anything that enters the domain of the spiny fish.

Also infesting this domain are the dramatically spiny sea urchins. Some species possess poison bags near the tips of the long, brittle spines. When trodden on, these spines puncture flesh and usually break off inside the resulting wounds, ensuring the prolonged insertion of the painful poisons.

Surprisingly, certain sea snails are also quite deadly. The seemingly harmless cone shells, attractively patterned and very slow-moving, can kill with their sting and human medicine has till date found no antidote. A harpoon-shaped tooth is thrust into the flesh of the victim, carrying the venom with it. Numbness, paralysis and eventually heart failure results. But the only way one of these snails will attack is if its soft parts are manhandled. Holding it by the hard shell is safe enough, although a steady grip is recommended.

Sluggish, bottom-dwelling scorpion fish and angler fish have flaps, projections and modified spines that give them the appearance of weed-encrusted rocks or bottom sediments. The angler fish even has a weed-like skirt around its entire body which disguises it on the rough sea floor on which it sits. If a small fish should venture near the large, wide mouth, it opens in a flash and the prey is drawn in with the inrush of water.