Fiddler Crabs – A Complete Guide (Care, Diet, Facts)

Some people are content with having a hermit crab, some people enjoy aquariums with fish, and sometimes, you need to branch out and consider adding the versatile, attractive, amusing and clever fiddler crab to an appropriate aquarium or even start having a fiddler crab tank as your pets.

If you are ready to take your aquarium set up to the next level, fiddler crabs are one of the most affordable additions available and easy to care for. If you are creating a diverse paludarium with live plants and fish, a fiddler crab can have an important role in the ecosystem.

Fiddler crabs are easy to care for and have a peaceful temperament if not in an environment shared with fish. They are not aggressive but will try to grab a fish that gets to close and are amusing to watch in a community aquarium setting. Fiddler crabs are normally brown and neutral hues for camouflage but there are fiddler crabs in every color of the rainbow. Male crabs often have a colorful dominant claw. The fiddler doesn’t live very long but replacing your crunchy grabby friends every two to three years is possible with pocket change.

They are small creatures and don’t require a lot of space and require a habitat with a dry area so they can sometimes get out of the water. Fiddler crabs are escape artists as well and need a secure tank top to prevent them from hopping out of the tank and taking a tour of the house that can risk their life. Having a lockdown or weighted top on the tank is a necessity.

Fiddler Crabs Overview

Fiddler crabs are found all over the world. Fiddler crabs are from the Uca genus of crabs and include over 94 different species. They are related to ghost crabs and the ancient Romans even ate them. They typically like to live in the areas where freshwater and saltwater bodies meet.

They are happiest in inter-tidal environments and coastal areas like salt marshes, mangroves and coastal estuaries where the water is slightly salty. The fiddler crab needs some salt in their water to thrive. Pet stores often do a disservice to the species and sell fiddler crabs as freshwater pets, but they suffer greatly in freshwater environments. In a freshwater tank, they will not be their most exciting due to poor health and will not reach their normal lifespan.

Appearance

Fiddler crabs are small crabs and typically are two to three inches in size. Fiddler crabs are invertebrates meaning they have no spine. They have a hard carapace that contains their internal organs. They live in their shells and shed them regularly as they grow. Fiddler crabs have four pairs of legs and two claws. Having ten legs (claws are their front pair of legs) place them in the small Decapoda classification of invertebrates.

The males are very different in appearance from their female counterparts. Male crabs have one very large claw and one small claw. The males use their large claw as a tool, a way to attract lady fiddler crabs and use their smaller more functional claw to eat. The large often differently colored large claw of a male fiddler crab cannot help it eat so females are more efficient at eating but not as exciting to watch. The fiddler crab has its mouth in the middle of its body.  Female fiddler crabs have matching small claws. The eyes of the fiddler crab are on the front of their heads and their eyes are on stalks. The eyestalks of a crab can move independently.  Fiddlers also have antennae on their heads that gather environmental data and use it.

Behavior

As the fiddler crab prefers living on the coast, they like diverse environments.  Most species are semi-terrestrial and spend some of their days on dry land and the rest of their day underwater eating and exploring their environments. Some also enjoy burrowing in their aquarium substrate where they will pop out to grab a meal. An important skill for living on the coast is the ability to survive both in and out of water. These crabs are semi-terrestrial meaning that their time is split between sitting on land and being submerged in water.

To enable them to live on land and still breathe underwater, the fiddler crab has a primitive lung system and gills. Often a crab will find a place to perch that has them only partially submerged. They need a tank set up that provides them will a place outside the water, many enjoy having a sandy little beach or rock outcropping to hang out on during their terrestrial time. Fiddlers crabs can live for months underwater, but they shouldn’t, and it isn’t good for them.

Fiddler crabs are social creatures and it’s always ideal to purchase a pair of male and female crabs. Two male fiddler crabs can butt heads and claws and make poor roommates compared to a male and female sharing their living space. Male fiddler crabs can fight if there are not female crabs in the environment and the physical altercations can lead to the weaker crab possibly losing its large claw.

Fiddler crabs regrow their lost claws and the claw that was not lost compensates by growing larger during the process so one claw will always be bigger and more dominant in a male fiddler crab. Having a mostly female crab community with only one of two males is best. Because of their social behavior, they will live with piranhas in captivity without the fiddlers being attacked by the piranhas and the piranhas knowing to not get in between fiddlers and floating food particles.

The piranhas learn to avoid the fiddler crabs as fiddler crabs will grab at a passing piranha to try and grab a chunk as a meal when hungry. Crabs use their claws for digging burrows as well as weapons. Fiddler crabs have some primitive means of communication with each other using their claws to move up and down and around.

They use their claws to sort substrate for food and will often eat substrate and leave balls of processed cleaned of all algae, plankton, and detritus behind. They will not breed in captivity because fiddlers only breed in deeper saltwater and you will not have to worry about a population explosion in your tank. You may see eggs in a fiddler-only environment, but these are infertile.

Breeding Fiddler Crabs

Fiddler crabs cannot breed in captivity. Pet fiddler crabs may mount each other as if mating but need ocean currents, deep water and high salinity to reproduce and release fertile eggs.  Fiddler crabs require to be in deep salt-water and always swim out into the ocean to mate. Larvae require phytoplankton to survive and ocean water to grow.

Pet female crabs may very rarely lay eggs in deeper water habitats. These eggs are defective eggs and cannot be fertilized. Other bottom feeding fish, the crabs, and brave fish will eat any eggs from a female who releases a clutch of sterile eggs. Having female and male crabs in a shared tank will not result in offspring.

Random Fiddler Facts

Fiddler crabs are omnivorous detrivores. They not only will eat anything, but they like to eat anything dead that drifts down within grabbing distance. They make excellent tank cleaners as they are omnivorous will eat algae in the tank as well. Fiddler crabs are meticulous about being a great detrivore.

They will pick through their substrate to find every speck. It also means they will hide the evidence if a fish in the tanks dies or is killed by them. If you’ve ever seen the cult classic film Pulp Fiction, a fiddler crab is just like the character Mr. Wolfe in that movie.

Setting Up the Rome for a Fiddler Crab to Rule in

An aquarium for a fiddler crab must have water, shoreline, and land. Building these with a soft sandy substrate is ideal.  Typically, fiddlers do not like gravel. Using some aragonite substrate will help maintain higher pH levels and provide a source of calcium and important trace minerals.

The Fiddler Crab aquarium habitat can have rocks, driftwood, and normal aquarium accessories to provide additional hiding places and climbing areas. The sandy substrate should be added in such a way it slopes up to a raised area of the tank. Fiddlers will burrow and dig on land and underwater.  A filter system and bubbler can ensure proper water cleanliness. The Fiddler Crab is an expert escape artist, so a tight-fitting cover is essential.

A habitat for either just fiddler crabs or fish and crabs needs to have a space of at least 4 inches or be only 2/3 full so the fiddler crab cannot find a way to escape. Even having a plant that extends to the top of the tank beyond the waterline is a way for a clever determined crab to get out. They have even been known to climb up filter tubing and decorations to leave the tank in search of new foods and adventures.

A bubbler oxygenates the water better and adds some additional water movement. All fiddler crabs need filters and/or bubblers to aerate their water due to their natural habitat being oxygen-rich and below or at sea level. They do not live in still water and the moving water sometimes delivers delicious treats directly within claws reach. Each week do tank maintenance and care.

Remove uneaten food, clean filters and make sure your crab is healthy and looks well. Many owners replace 10 to 20 percent with freshly conditioned water. If the water has food remnants floating or plant pieces, a daily skimming can prevent problems caused by rotting food and vegetation.

Fiddler crabs prefer brackish water and need some salt in their aquariums for the best health. Freshwater tanks can kill most fiddlers within a few months. Adding a marine salt block in the tank to dissolve slowly or adding a teaspoon of aquarium (or marine salt) for every 10 gallons of water will not harm your freshwater fish even and will help your fiddler crab healthier.

The goal measurement for salinity is between 1.01 and 1.08. Hydrometers and testing supplies for saltwater tanks are easily available at pet stores and online. Always dechlorinate water and add a small amount of salt. Marine salt is different than Aquarium salt and while that choice is up to the owner, most crabs thrive in marine salt.  A fiddler crab prefers a tropical fish temperature range and heating bulbs or other heat sources keeping the aquariums temps at a balmy 75-86°F. They also prefer a slightly alkaline environment with the pH being in the 8.0-8.3 range and a hardness 15 KH.

Fiddlers also need space. 2 crabs can share a 10-gallon aquarium but each additional crab you’d add would need another 3-5 gallons to prevent overcrowding, bad behaviors, and illness.

Unlike some types of fish, a fiddler will not grow to fit their tank so you can have a 200-gallon aquarium shared by several fiddler crabs, fish, and live plants and not have to worry about the fiddler crabs ever becoming as large as a Japanese spider crab. Many crabs come in 5-gallon freshwater tank setups like betta are sold and that is acceptable but will not provide you with as much enjoyment from your crab and will shorten their lives.

Fiddler Crab Roommates

While having just a fiddler crab set up is an easy-care pet, many people with aquariums want to add a fiddler crab to an already set up aquarium to clean the tank of any food particles the fish miss and, as detrivores, they are eating machines. Crabs eat fish, however. Bottoms-feeder fish that are usually kept to help clean a tank can be replaced with a fiddler and if a fiddler is added into a tank with Oscars or other algae and tank-cleaning fish, they will get attacked and eaten by the crab.

Never place a fiddler crab in a tank with goldfish or with a betta. Goldfish are cold-water fish and cannot tolerate the heat a fiddler needs, and their fins are inviting waving buffets for a curious and hungry fiddler crab.  Bettas are also known as Siamese Fighting Fish and are an aggressive fish. The fiddler crab and betta will have conflict and one will get injured or killed. The necessary isolation of one fish per bowl required for a betta is a recipe for disaster if shared with a fiddler crab.

Fish that share a tank with a fiddler need to do well in slightly brackish water and any people have fiddler crabs in their mollies or neon tetra tanks with success as these fish do well in the ideal fiddler crab water conditions and are fast swimmers that stay in upper half of the water usually, even when schooling.

Other people have good luck with guppies who are not mating as they have live births, bumblebee gobies and glo fish also do well. Barbs, zebra danios and platies can also share a tank with minimal risk to the fish.

Snails, especially the nerite snail that lives in brackish waters, do well as a tankmate but be aware that if the fiddler crab can reach the gastropod, it will quickly become a gastronomical treat for the crab. Ghost and Amano shrimp also thrive in the ideal fiddler tank so while they risk being eaten, they can coexist.

Never overcrowd the tank. Overpopulation in a tank will force more fish to go to the bottom of the tank. Other bottom-feeding fish should not be in a fiddler-inhabited paludarium.

Fiddler Crab Diets

Fiddler crabs as pets are opportunistic feeders. They eat anything. If they cannot eat it, they will still pick it up, try to tear it into bite-sized bits and will spit it out. They use their claws as hands. If you have a fiddler-only tank, any fish food for scavengers such as shrimp pellets, algae wagers, commercial crab food, dried worms, shrimp and krill provide the necessary protein a fiddler crab needs.

If you do not have edible plants in the aquarium, many fiddler crabs enjoy teats of blanched zucchini, peas, seaweed, and romaine lettuce.  You can offer blanched zucchini, blanched peas, and raw or boiled fish. They will also eat freeze-dried plankton and shrimp. A small bit of raw fish is also a nice snack.

Providing direct to the crab food sources and a varied diet will ensure they grow properly and get the right nutrition. Sinking pellets will ensure a crab gets food in a shared habitat. If the tank gives off an odor of ammonia, the tank has too heavy a bioload for the fiddlers to keep up with and they are being overfed.

Do a gradual water change over the course of a week, remove all floating debris and clean the filters to improve the water quality and eliminate the odor to keep your crabs healthy.

Crabs even recycle their own shed carapaces to get the calcium needed to harden and build strong shells. A fiddler crab that is healthy will grow out of their shell and molt. A molt looks like an empty fiddler crab.

A balanced diet provides the calcium, but a molted shell should be left in the tank for a week or two to allow the crab to graze on it for additional calcium before removing it. Crabs never waste anything. If you notice a crab aggressively and actively hunting, you need to provide more food to your crab.

Choosing a Healthy Pet Crab

Try to find a pet crab that is in the right environment when looking for a crab or preferably, two. The common red claw is a coastal crab so it should not be tagged as a freshwater pet. Never buy a “freshwater fiddler” if possible. If the only source of fiddler crabs available are listed as freshwater, wait until the next batch arrives to get a crab that has not lived in freshwater for as long.

Choose a healthy-looking crab with good coloration, no discolorations or signs of algae or fungus on their shells. Count their legs and claws and make sure there are ten of them and all are intact. While lost legs and claws grow back after several molts, you do not want to buy a damaged pet. You can expect to pay an average of 5-12 USD for a fiddler crab depending on the size, age, and type of crab.

Being a Fiddler Owner

Fiddler crabs make excellent pets because they are relatively low maintenance and if not overfed, keep their own tanks clean and tidy. Fiddler crabs are a low-cost pet that has a unique lifestyle and can provide necessary janitorial services to warm water saltwater or brackish aquarium. The fiddler crab is more exciting to watch than fish that merely attach to the glass or lie on the bottom lazily as they do their detrivore job.

They can be quirky and fun pets. Each crab has its own unique personality and behaviors and it can be fascinating to watch them climb and scuttle about their tanks from their driftwood beach cabanas to their bolt holes at the bottom of the tank. Providing a diverse, healthy and stimulating habitat for a fiddler is fun and provides you with a great aquarium watching experience.

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