Gobies are the largest fish family in the world with over 2000 species. Most of them are camouflaged bottom-dwellers and carnivores. Some species also eat plants and detritus.
They live in symbiosis with one or more almost blind pistol crabs. The crab takes care of the living tube and the goby is on the lookout. In case of danger the goby warns with fast tail movements.

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