Conger eels live in small to huge colonies in sandy areas, usually near drop-offs or reef edges. Each tube eel lives in its own self-dug tube and never leaves it. They feed on plankton.
In addition they come to two thirds of their tube and catch this from the current. They are very shy and retreat into their tubes in time as soon as a predator or larger creature such as a diver approaches.

Excerpt from "Life in the Red Sea." iBooks.