What’s the difference?
A poisonous fish is one that is toxic to eat, such as puffer fish and toadfish. These colourful characters harbour a strong poison in glands in their bodies, and when they are eaten by other fish (or people!), they can cause illness or even death. Puffer fish have an alternative defensive mechanism where they can inflate their bodies to create the illusion that they are larger than they actually are, which will often scare of potential enemies. However, if they over inflate their bodies, they can induce heart failure (in themselves!). In Japan, highly skilled chefs use parts of the blowfish (a closely related species) to create a dish called “fugu”, with just enough of the tetrodotoxin poison to give the meal that “special flavour”!
Venomous fish, on the other hand, are ones that cause an envenomation, usually through a penetration wound, such as a spine. Some fish, such as the infamous stone fish, have highly toxic glands at the base of their spines, and when people stand on them, the pressure forces the venom into the victim. Although it is extremely painful, it is rarely lethal, and an antivenom is available for severe stings. Stonefish stings are generally the most severe, as they have neurotoxins in their venom, but there are others, such as lionfish and stingrays. Lionfish have elaborate pectoral fins, attired in the warning colours or orange and red. When they are actively hunting prey, they herd their victims up against the coral, spreading their venomous arrangement of spines in a rainbow of colour so they can’t escape.
Stingray envenomations usually occur when theyare trodden on or handled by fishermen. The natural reaction for a stingray that is used as a doormat is to thrust backwards with the spine located on its tail. The spine is designed to easily penetrate but not to be easily removed. The venom around the spine can cause infections and sometimes necrosis (death) of the surrounding tissues.
The best treatment for an impaling wound is heat, as heat denatures the protein of the toxin, and converts it to a less dangerous compound (and it also helps alleviate the pain!). It also increases blood flow and helps disperse the venom. The water temperature shouldn’t be any more than 50°C, as anything above this could burn your skin. Keep a close watch over the next few days for possible infection, and seek medical help if necessary. The victim should be OK in a few days.