Not to mention wiping out tanks themselves..lol
I've read at least one article on them..max size is about 7" right ? Must have smaller eels...a medium sized funebris or moringa would consider them chow..heh heh eels really don't have many predators..having toxic flesh helps that..but their only tools are teeth..so every problem is viewed as food.
Every problem isn't necessarily food, per se. It's just the only way in which the eel has to interact with its environment. It's the common misconception people have with "dangerous" animals is that anything and everything is on their menu, when simply its their curiosity which makes them seem like these mindless beasts which just kill and eat indiscriminately.
There are well over 400 species of Mantis shrimp, and some can get to be up to 14-15" long, 10" around the average. Eels actually do have predators in the wild. Aside from sharks, large octopi have been known to prey on them regularly. As much as I love eels, they are still another link in the food chain.
Shot an e-mail to a friend who keeps a fair number of saltwater tanks, as well as a number of eels and stomatopods, along with a glut of other creatures. He said he's been forced to keep his large adult Peacock Mantis separate from all of his other aquatic pets, as it regularly decimates them, eels inclusive (doesn't help that he's had to replace two tanks now because of the Mantis' claws, which strike with the strength of a .22 bullet). He said once when one of his Whitemouth morays, known to specialize in crustaceans, made an attack on his Peacock Mantis (apparently at least 5" smaller than its present 13" at that time), the Mantis literally wheeled aside, delivered a few quick blows just behind the eel's head, and he was out $130.
And he couldn't get the eel out of the tank. The Mantis dragged it half into its coral den and devoured it over the course of several weeks, attacking any net he attempted to put in until he just gave up. Both are exceptional predators, but I make a practice not to bet against stomatopods. The spearer varieties of Mantis shrimp have been known to kill 5' nurse sharks.