Lightning damage, and visually they crackle with lightning as well.
"The electric eels are insidious pests that have taken root in the oases surrounding Caldeum. Known for their stinging strikes, these creatures are particularly dangerous when they attack in large numbers. It is said that raw eel has become a delicacy among Caldeum's elite, but I assure you these rumors are baseless."— Abd al-Hazir(src)
- The lore entry is a possible pun towards the real-world eels, who are often used as a raw ingredient for sushi.