The two predators have complementary reach. A grouper hunts in open water and cannot follow prey into a crevice. A moray moves through the reef interior but is slow in the open. A fish that hides from one is exposed to the other.
Field work in the Red Sea documented a specific signal: the grouper approaches a moray, positions itself close to the eel's head, and performs a rapid lateral head shake. Morays follow more often after the signal than at random, and joint forays capture more prey per unit time than either predator hunting alone. Groupers also perform a headstand and point their body at a crevice where prey has hidden, which is a rare example of referential gesturing outside mammals and birds.
There is no sharing. Each predator swallows what it catches whole, so the arrangement is mutual benefit through increased hunting success rather than cooperative food division. Whether groupers select individual morays by past performance has been reported, and how far the behaviour extends beyond well-studied Red Sea sites is not established.