The Gas Eel of the Amazon Basin has no natural enemies. This eel eats a diet consisting entirely of rotting vegetation, due to its underdeveloped teeth, which means it has little capacity to chew its food. These eels can grow to be 10 feet long and weigh about 70 pounds, although roughly 20 pounds of this weight will be gases such as methane.
If the eel is feeling lazy, it can propel itself by emitting quick bursts of gas which will power it through the water for distances of up to 50 metres. These bursts of gas can have a detrimental effect on the health of nearby fish, so if animals see a gas eel approaching, they will normally scatter or swim ahead of it so as to avoid the pungent aroma.
This is an extract from the book Animals Evolution Avoided