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Sunday 23rd October 2016

Stingray tragedy for Steve Irwin

5th September 2006

05092006_stingray1.jpgA fatal attack by a stingray, as on Australia's "Crocodile Hunter" Steve Irwin, is almost unheard of.

Stingrays are normally placid fish whose larger species are occasionally known to tolerate the efforts of scuba divers to ride them by clinging to their fins. However, when they feel threatened or are trodden on, they are capable of causing injury by lashing out with the razor-sharp, barbed sting at the end of their tails.

The barbs are designed to snag in the flesh of the victim, with each barb being serrated, up to 20cm (8ins) long, and coated with a paralysing toxin which the ray secretes along two grooves in its tail.

Stingray injuries are common, but most wounds are sustained to the legs or feet when stingrays are trodden on in the shallows. The stingray’s toxic barb is broken off and remains in the wound, especially when the fish is pulled off the victim.

However, very serious injury or death can occur when the barb enters the body through the chest area, so that the heart or other vital organs are damaged and the poison is administered directly, causing the blood vessels to constrict.

The deputy director of the Australian Venom Research Unit at the University of Melbourne, Dr Bryan Fry, said stingray venom was a defensive weapon similar to that in stonefish, whose poison is generally fatal, but in the stingray's case the toxin was not lethal. He said that it was the serrated barbs on the stingray's tail that would have delivered the fatal injury, with the deep serrations tearing the flesh as it is withdrawn. 

A clinical toxicologist, Dr Geoff Isbister, agreed it was the physical trauma associated with the wound that would have killed Irwin, and that little was known about stingray venom.

All stingray venoms are similar, containing serotonin, 5-nucleotidase, and phosphodiesterase. The latter two enzymes are responsible for the necrosis and tissue breakdown seen in stingray attacks; serotonin is the cause of inexorable pain in the injury. Clear cause and effect reactions from stingray injuries are not readily understood.

Irwin’s death was only the third known stingray death in Australian waters said Victoria Brims, a shark and stingray expert. Only 17 such deaths have ever been recorded worldwide; an aboriginal boy died several years ago, and the previous record death was in Melbourne in 1945.

The largest species of stingray can grow to more than 7ft (2m) in width and their tails can be twice as long as their bodies. The animal has a reflexive defence mechanism causing it to strike the victim with its tail when it feels threatened, which it may have felt in the case of 
Steve Irwin.

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