The weird and wonderful world of electric eels

Here's another in my occasional series about weird and cool animals (see the entry on tardigrades, for example).

Electric eels, it turns out, are not actually eels. They are eel-like in shape, but they are technically a type of knifefish (they have actually been reclassified several times since Linnaeus first classified them back in 1776). What else do we know about them?

• They grow up to 2 metres in length, and a full-grown adult may weigh up to 20 kilograms. 
• They can be purple, grey, blue, black or white in colour, and do not have scales like most fish. 
• They are only found in the Orinoco and Amazon rivers in South America. 
• They have poor eye-sight but an acute sense of hearing. 
• They live in water and have gills, but actually breathe air (they surface about every ten minutes or so to breathe). 
• They are carnivores and eat other fish, small mammals, birds and amphibians (very young electric eels are quite happy to eat unhatched eggs and other eels).
• They live for around 15 years in the wild, and up to 22 years in captivity.
• They use three different organs in their abdomens to create electricity (which together make up most of their body mass). Two of these organs are used to shock their prey, the other is used for "electrolocation" (they have frequency-sensitive receptors on their skin that can sense electromagnetic fields).
• A shock from an electric eel is enough to knock over, but not kill, a human, although it can cause heart attacks in those who are prone to them. The eel itself is insulated, and so immune to its own electricity.
• There are about 500 other species of electric fish, including electric rays and several species of electric catfish.

Cool or what?