One thing that makes the coral reef ecosystem so amazing is all the symbiotic relationships that occur between the reef’s residents. One of the most popular is the mutualistic association between sea anemones and anemonefish (clownfish).
But I would argue that the most incredible partnerships occur between some species of gobies (around 120 species) and certain shrimp in the genus Alpheus (these are called pistol or snapping shrimp). These shrimp create extensive burrow systems in the sand adjacent to coral reefs. While they create enviable sanctuaries, they have one problem: when they are pushing sand out of their ever-collapsing burrows they are vulnerable to predators because they have poor eyesight. They solve their problem by enlisting the aid of seeing-eye fish — a group of gobies that live with the shrimp and let them know when danger is impending. When the shrimp is pushing sand and debris out of its burrow, it rests its antennae on the tail of the goby. When a threat is too near, the goby wags its tail and the shrimp takes shelter. Fortunately for us, this association is easy to set up in the home aquarium and fascinating to watch!
Difficulty: One of the most common shrimp-associated fish is the yellow watchman goby (Cryptocentrus cinctus). This species is also referred to as the banded shrimpgoby or yellow shrimpgoby. Not only is the yellow watchman goby very durable, but it can also be quite attractive! The yellow watchman goby will readily acclimate to the home aquarium, even if a pistol shrimp is not provided, if the aquarium is replete with shelter.
Feed the yellow watchman goby every other day in a reef aquarium or once a day in a more sterile fish-only system. Foods of choice include frozen preparations for marine carnivores, frozen fish eggs, frozen Cyclops and even flake food. While the yellow watchman goby will typically scavenge and will get enough to eat by grabbing food that hits the aquarium bottom, I occasionally target-feed. I take a turkey baster with a piece of air-line tubing attached and direct some food into the yellow watchman goby’s burrow entrance.
Physical description: The yellow watchman goby exhibits several different color forms. The most abundant “flavor” is a yellow form with blue spots, but there is also a color form that is lighter in color with brown banding and another that is dark brown overall. It is most similar to the barred shrimpgoby (C. fasciatus), but this latter species has no markings on its dorsal fin. The yellow watchman goby can reach a length of around 3 inches.
Range: The yellow watchman goby is a resident of the western Pacific, where it ranges from southern Japan to the Great Barrier Reef. The yellow watchman goby lives on shallow sand flats and slopes in bays, lagoons, on back reefs and reef slopes at a depth of between 18 to 80 feet. The yellow watchman goby typically is found on sand or mixed-sand-and-rubble bottoms.
Compatibility: The yellow watchman goby is not overly aggressive toward tankmates. That said, larger yellow watchman goby (and other larger members of the genus Cryptocentrus) tend to be more aggressive toward other shrimpgobies than some of the other crustacean-associated gobies (e.g., Amblyeleotris spp., Ctenogobiops spp., Stonogobiops spp.) if bottom space is limited.
If you keep more than one C. cinctus in the same smaller aquarium, add them simultaneously or introduce a smaller specimen first. In an aquarium with a larger surface area (i.e., more useable living space), with lots of hiding places, aggressive encounters will be nil or limited in occurrence. It is a possible that C. cinctus will be picked on by dottybacks, larger damsels, hawkfish and sand perch. Its elongate body shape makes it easier to eat for frogfish, scorpionfish and groupers.
Aquarium conditions: While the yellow watchman goby can be housed without their shrimp associates in aquaria, they are certainly much more interesting to watch if shrimp and goby are kept together.
The goby and shrimp do best in an aquarium with a deep-sand substrate. Make sure you place the rockwork on the bottom panel of aquarium glass and place the sand substrate around the rock, rather than placing the sand on the aquarium bottom and putting the rock on the sand. To facilitate burrow construction, mix some pieces of coral rubble, small pieces of live rock and medium-sized shells with the sand so that burrow construction isn’t impossible. Keep the water parameters for the yellow watchman goby at a pH of 8.1 to 8.4, specific gravity of 1.019 to 1.025 and a water temperature of 74 to 82 degrees Fahrenheit.
Care considerations: When initially introduced to the aquarium, it is not unusual for the yellow watchman goby to hide whenever you enter the room. But, it will gradually become accustomed to your presence and allow you to observe it at close range. Cryptocentrus cinctus are also good jumpers and often end their lives by leaping out of open aquariums or through holes in aquarium tops.
The yellow watchman goby will associate with the tiger pistol shrimp (Alpheus bellulus) and Randall’s pistol shrimp (A. randalli) — the two most common species available to aquarists.
Breeding: If you can acquire a pair of yellow watchman goby, they will spawn in the home aquarium. Sexing the yellow watchman goby is not easy, but females are usually bigger than their male partners. The female lays her eggs in the burrow. The pair protects the eggs vigorously and may cause problems with their fish tankmate neighbors in a smaller aquarium. The eggs hatch in about five days (this is temperature dependent). Feeding the larvae is difficult, with suggested first foods to include rotifers (Brachionus rotundiformis).