Watchman Goby (Cryptocentrus cinctus)
Watchman gobies (Cryptocentrus cinctus) are interesting marine fish from the family Gobiidae. The name watchman goby is derived from their large protruding eyes and from their tendency to stand guard (as if on watch). These gobies are also commonly called yellow prawn gobies because of their symbiotic relationship with the pistol shrimp (see more about this below).
Their natural environment is in the Indo-Pacific where they inhabit shallow ocean waters with sandy bottoms.
Watchman gobies are relatively small fish that only reach about 3 inches (7.6 cm) in length. They are peaceful bottom-dwelling fish, although they occasionally become territorial in small aquariums. A mated pair can be succesfully kept.
They are carnivorous fish that need to be fed a meaty diet of vitamin enriched brine shrimp, mysis shrimp, finely chopped seafood, and frozen commercially prepared food for marine fish.
The watchman goby, as well as all of the other "shrimp gobies" has a symbiotic relationship with the pistol shrimp (Alpheus spp.). The shrimp and the goby typically live together in a burrow that the shrimp excavates. The goby and the shrimp look out for one another. The yellow prawn goby (watchman goby) stand guard and when a predator comes near both the goby and the shrimp hide in the burrow created by the shrimp. Watch the short You Tube video below for a demonstration of this relationship between a watchman goby and a tiger pistol shrimp (Alpheus bellulus).
As you can see from the video the shrimp is busy excavating a burrow while the goby stands guard. In general, the gobies have much better eyesight than the shrimp and so the goby warns the shrimp when a predator approaches.
If you plan on keeping a watchman goby in your aquarium then you should also keep the tiger pistol shrimp along with it. The pistol shrimp is also a carnivore.
Because of their burrowing behavior you need to have a sandy substrate with some loose coral rubble as well as some live rock for caves and crevices. They will also graze on the inhabitants of the live rock.
Yellow watchman gobies can be purchased for about $15 each. Its "friend," the tiger pistol shrimp, can usually be purchased for about $20 each.
Both the goby and the pistol shrimp won't harm your coral reef.