Fiddler Crabs as Pets

   

Ron Hines DVM Ph.D

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Introduction

As individual pets, hermit crabs have much more personality than fiddler crabs. But if if you want a shared environment including crabs and fish then fiddler crabs are for you. There are over 90 species of fiddler crabs. All belong in the genus, Uca. 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.

Where To Get Your Fiddler Crab

The fiddler crabs sold in pet stores generally come from brackish water lagoons. Because they live in lower salinity water, pet stores may call them fresh-water crabs. Regardless what your are told, they can not survive indefinitely in fresh water. Try to purchase crabs that have not been stored in fresh water more than a few days. Pick individual crabs that are perky and active and that have all their claws and legs. If you live in a coastal area you may be able to find fiddler crabs in mud and sand inlet beaches and marshy area at low tide.

Setting Up The Aquarium

The first thing to do is to buy your aquarium. A ten gallon aquarium will house four medium size 1-2 inch) fiddler crabs with sufficient space to prevent aggression. Prepare a sloping sand area for the crabs to bury themselves. If you add brackish water fish to this habitat you will want a larger aquarium. Fish such as platies, mollies, guppies and swordtails as well as ghost shrimp will adapt to moderate salinity. Set up some type of bubblier aeration system to oxygenate the water.

Water Quality

I prepare a brackish water solution by adding two and one-half teaspoons full of sea or aquarium salt to one gallon of water. If you have a hygrometer, attempt to reach a specific gravity reading of 1.01-1.08. Let the water sit overnight so that chlorine and chloramines dissipate. I change the water every two weeks but you can add at biowheel ammonia and nitrate removal system so you do not have to change the water.


Carbonate Hardness (KH) and pH

Fiddler crabs do well with a pH or acidity of 8.0-8.3. Purchase as KH test kit as well. Carbonate Hardness (KH) should optimally be between 150-350 ppm but crabs and some fish will tolerate a much higher levels.


Substrate

Fiddle crabs do no do well if they do not have access to dry beach sand or dry to moist rock surfaces. The easiest way to obtain a “beach” is to taper a sandy slope into the water. Triple-washed masonry sand makes a good “beach” for the crabs to get out of the water. Although the crabs seem to do as well using gravel they enjoy digging in the sand more.

Temperature

Fiddler crabs do well in a range of temperatures between 75-85 F (24-29 C). If you keep fish in the tank the temperature may need to be regulated more precisely.

Diet

Fiddler crabs are normally scavengers feeding on microscopic dead organic mater, plants, algae and animals.. In the wild, they find this food in the sand or mud. Female crabs feed with both claws. The large claw of males is a display apparatus to attract females and is not used for feeding. In aquarium situations feed the crabs sinking crab food, shrimp pellets and freeze dried shrimp and plankton. You can supplement their diet with seaweed purchased from an oriental foods market, sliced zucchini, fresh fish, and aquarium seaweed. Do not foul the water with excessive food.

When crabs molt, allow them to eat the shed exoskeletons. This gives them an additional source of calcium.

Fiddler Crab Health

Fiddler crabs that are healthy will grow and molt at regular intervals. Missing claws and legs will regenerate over several molts. If the large showy claw is lost to a male it will regenerate over several molts on the opposite side.

Male fiddler crabs are territorial. They will fight to protect their turf. To prevent this, do not place too many crabs in the tank. Females are less aggressive.

Specific disease among captive fiddler crabs is rare. Most problems result from improper salinity, pH or temperature or too many crabs in a limited area. Crabs also die if they were kept in fresh water at the pet store.

Calcium and Iodine

Calcium and Iodine are required for molting. Calcium is also required for proper nerve function. The best source of these micro-nutrients is a product such as instant ocean.