Fiddler Crabs (Uca ssp.)
Fiddler crabs are among the most active and interesting crustaceans that may be kept in the aquarium. Although a bit of work must go into their care, the fascinating behavior exhibited by a colony of fiddler crabs renders the effort worthwhile.
Fiddlers are semiterrestrial crabs that form huge colonies on tidal mud flats throughout the world. Either the right or left claw of the males is greatly enlarged and is used for territorial signaling and defense. These signaling motions seem reminiscent of a person playing the fiddle and have given rise to the animal's common name.
Each fiddler crab constructs a burrow into which it seals itself at high tide. As the tide recedes, the crabs leave their homes and forage in the mud for organic detritus, algae, and the remains of deceased animals. Fiddler crab colonies may contain millions of individuals.
A colony of fiddler crabs will present you with countless hours of entertainment. Once acclimated to captivity, fiddlers quite readily go about their usual activities, constantly foraging and squabbling over territories. Although males are intolerant of each other, they quickly establish territorial boundaries and fights are rarely serious.
To observe their natural behaviors, you should provide your fiddler crabs with a mud or sand beach. The substrate should be 6 to 8 inches deep so that the crabs may construct comfortable burrows. Newly introduced crabs may take several weeks to settle in and will only rarely show themselves during that time. Eventually, however, they will become quite bold and hearty captives. Strangely, fiddler crabs seem completely unaffected by the lack of tidal influences in captivity and soon establish their own pattern of active and resting periods.
The world's tidal areas are home to countless species of shrimp, crabs, oysters, spiny lobsters, and other invertebrates. These creatures are most often kept in marine aquariums but actually adapt to, and may even prefer, brackish water.
These crabs cannot swim but will enter shallow water and walk about on the bottom. It is critical that they are provided with simple methods of leaving the water section of their aquarium. Be sure to include a number of sloping areas and rocks. Fiddler crabs may also be maintained in a terrarium partially filled with mud that has been saturated with saltwater. A bowl containing saltwater for soaking should also be provided. This method of maintaining the crabs offers the advantage of providing them with a greater land surface and allows for a more expansive burrow system.
Fiddler crabs find food by using their tiny claws to sift through the mud at low tide (the male's one large claw is not used for feeding). They do quite well on a diet of moistened fish flakes and pellets. Spread the food evenly around on the mud, because the crabs will exclude others from the immediate vicinity of their own burrows. Fiddler crabs also relish small bits of fish and shrimp. Mud collected at local shorelines will provide them with a valuable source of natural food items.