Fiddler Crab (Uca pugnax)
From The Aquarium Wiki
19 Litres (5 US G.)
2.5-5.1cm (1-2 ")
7.5 - 8.2
23.9-29.4°C (75 -85 °F)
Alternative names[edit | edit source]
- Fiddler Crab, Calling Crab, Mud Crab
Sexing[edit | edit source]
- Male Fiddler Crabs have one big claw and one small while females have two smaller claws.
Tank compatibility[edit | edit source]
- Really best kept in species tanks and can live with other crabs but may fight with other crabs if not enough space to set up territories, but if kept with fish they must not be kept with long-finned fish, bottom dwellers or small fish species. Top dwelling and fast-swimming fish that prefer brackish conditions only.
Diet[edit | edit source]
- An omnivorous crab which will take most foods including blanched vegetables, flakes and pellets, brine shrimp, bloodworm and fish.
Feeding regime[edit | edit source]
- In the wild fiddler crabs are scavengers, eating bits of organic matter they find in the sand/mud. In captivity, they can be fed sinking crab food, fish food meant for scavengers (sinking tablets, shrimp pellets, etc), and freeze dried plankton and shrimp. Signs of health in fiddler crabs include growth and regular molting. Once a crab molts, their previous exoskeleton will likely be whole in the tank, looking eerily like a ghost. It is a good idea to leave the exoskeleton in the tank, at least for a week or so. Often the crabs will ingest part of the shed exoskeleton, and it serves as an excellent source of calcium (which they need to produce their new exoskeletons). Claws and legs may be lost but will regenerate over a couple of molts.
Environment Specifics[edit | edit source]
- Must have access to an area above the water line, and prefers brackish conditions, an SG of 1.005 is sufficient. A secure fitting lid is essential as these are excellent escape artists. Fiddler are particularly sensitive to copper, which is an ingredient in many fish-disease treatments and snail-eradication chemicals, avoid at all costs. The ideal amount of marine salt to add is controversial, but it is probably best to get a hydrometer and add enough salt to the water to attain a specific gravity of between 1.005 - 1.010.
Behaviour[edit | edit source]
- An active crab that climbs well. Fiddler will catch small fish and eat them if they can. Fiddler crabs are better-suited for a shared environment including crabs and fish. This crustacean is named for the fiddle-shaped large claw present on males. This entire group is comprised of small crabs – the largest being slightly over two inches across. Fiddler crabs are found along sea beaches and brackish inter-tidal mud flats, lagoons and swamps. Like all crabs, fiddler crabs shed their shells as they grow. If they have lost legs or claws during their present growth cycle a new one will be present when they molt. If the large fiddle claw is lost, males will develop one on the opposite side after their next molt. Newly molted crabs are very vulnerable due to their soft shells. They are reclusive and hide until the new shell hardens.
Lifecycle[edit | edit source]
- Fiddler crabs live rather brief lives of no more than two years (up to three years in captivity). During courtship, the males wave their oversized claws high in the air and tap them on the ground in an effort to attract females. Fights between other males will also occur, which are presumably meant to impress the females; if a male loses his larger claw, the smaller one will begin to grow larger and the lost claw will regenerate into a new (small) claw. For at least some species of fiddler crabs, however, the small claw remains small, while the larger claw regenerates over a period of several molts, being about half its former size after the first molt. The female fiddler carries her eggs in a mass on the underside of her body. She remains in her burrow during a two week gestation period, after which she ventures out to release her eggs into the receding tide. The larvae remain planktonic for a further two weeks.