This is the Yellow Watchman Goby and Tiger Pistol Shrimp that share a symbiotic relationship in my reef tank. The pistol shrimp is an excellent cave builder, but has poor eyesight. He provides shelter to the goby by sharing his home, and the goby returns the favor by warning the pistol shrimp of potential predators (such as the emerald crab in the corner). At the end of the clip the moon lights come in and they call it a night. See part 2 to view my goby and pistol working with crushed coral substrate.