Fiddler Crab 101: Care, Diet, Setup, Tank Mates & More!

Uca_sp.,_fiddler_crab_-_Tarutao_National_Marine_Park_(16491810210)
Dr. Mollie Newton
Published by Dr. Mollie Newton PHD| Senior Editor
Last updated: July 13, 2024
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If you’re looking for a strong brackish water creature that does well alone in a tank and has a distinctive character, the fiddler crab is an ideal choice for you. This guide leverages practical experience and comprehensive research to help you maintain a fiddler crab at the top of your aquarium. These small crabs can live comfortably in a 10-gallon desktop tank, always offering entertainment with their lively behavior.

Article Summary

  • Fiddler crabs have one enlarged claw, which they use for fighting, burrowing, and mating. This behavior resembles playing a fiddle.
  • Tankmates should be chosen carefully to avoid aggression, and recommended companions include other fiddler crabs, mollies, guppies, danios, cherry shrimp, while pufferfish, gobies, Mayan cichlids, and Siamese tigerfish should be avoided.
  • Fiddler crabs are suitable for beginner aquarists due to their low maintenance and entertaining behavior.

Species Overview

Common namesFiddler crabs, fiddlers
Scientific nameUca
SpeciesUca spp.
Size2 in
Lifespan2-3 years
FamilyOcypodidae
GenusUca
DistributionWorldwide
ColorRed, orange, white, yellow
DietOmnivore
TemperamentSemi-aggressive
Minimum tank size10 gallons
Place in the tankBottom
BreedingN/A

History and Background

These quirky crustaceans have been well loved in their natural environment so it’s no wonder that they have entered the aquarium trade as one of aquarist’s favorite crabs and are commonly found in pet stores everywhere.

What is a fiddler crab?

Fiddler crabs are a popular aquarium inhabitant and are well known for having one enlarged claw. The term fiddler crab actually refers to about 100 species and subspecies all a part of the genus Uca family Ocypodidae, and subphylum crustacea, phylum arthropoda. Fiddler crabs live along the coast, marsh, swamp mud, and wetlands worldwide and are hardy creatures well known for their feisty attitude.

TIP

Scientists classify crabs and other animals through a system called taxonomy. They start with the broadest category (Phylum) and each following category means that the animals within it are more closely related. In the paragraph above we start at the smallest taxonomy (species) and work our way up: genus, family, subphylum, phylum.

What are they called fiddler crabs?

The fiddler crab name comes from it having a large claw that’s held in front of its body and moves back and forth. While this behavior is to deter predators by making the small crab seem larger and help find mates, it also tends to look like it is playing the fiddle.

Where did the fiddler crab come from?

The natural habitat of most fiddler crabs include the coastal regions of Western Atlantic, Eastern pacific, Indo-Pacific, and West Africa. In other words at least one species of fiddler crab can be found almost worldwide.

Appearance

Close-up Photo of a Fiddler Crab
(1) Close-up Photo of a Fiddler Crab

The term fiddler crabs is very broad and includes many different species that have many different characteristics, colors, and patterns.

What do fiddler crabs look like?

While there are many different species of fiddler crab they all have the same basic body characteristics. They are small crabs that, like other crabs, have 10 legs and a hard shelled body. Female fiddler crabs have two small claws, whereas male fiddler crabs have one small claw and one major claw. The enlarged claw is used for fighting, burrowing and mating purposes, otherwise the male will rely on his smaller claw to eat.

While fiddler crab species are roughly the same size they do range in color and patterns, and variations are dependent on genetic differences and environmental health.

Types of Fiddler Crab

There are many species of fiddler crabs, we’ve taken the liberty of listing a few of the most commonly found at pet stores below.

Marsh fiddler crab

Minuca pugnax is commonly found in the marches of the western Atlatic (east coast of the U.S.). Both males and females are brown in coloring and tend to grow to a maximum size of 1 inch. The male crab has a patch of blue on the carapace which the females do not.

Spined fiddler crab

Leptuca spinicarpa is native to brackish water along the Gulf of Mexico. Though technically not part of the Uca genus any longer it is still often referred to as a fiddler crab. The species is yellow/brown in color and has a green tint along the front of the body. The oversized claw on the male has strong raised ridges.

Red jointed fiddler crab

Minuca minax is commonly found along the east coast of the United States. The body of this fiddler crab is yellow/brown but the joints on the claw are red, giving it its name. Females claws are equal sized and smaller than the males.

Sand fiddler crab

Leptuca pugilator mainly eats vegetative matter and can be distinguished from the previous freshwater crab because of the smooth (instead of serrated) edge of its claw. It is mostly red and brown colored.

How big does a fiddler crab get?

Fiddler crabs generally grow to a maximum size of two inches wide. Despite their large claw size these are very small crustaceans!

How fast do fiddler crabs grow?

It takes roughly 6 months for a crab to reach its mature size.

What does a molting fiddler crab look like

It is normal for crabs and other species of crustaceans to molt as they grow. Molting looks similar to a snake shedding its skin, with a layer of collagen peeling off of the body. You should never touch an animal while it’s molting as they will (1) likely be very grumpy and more prone to bite and (2) the new shell underneath the molt will be soft and squishy, interfering with this could harm or disfigure your crab.

FUN FACT

If your crab has lost legs or has a lost claw they can molt and regrow it. While the new appendage will be smaller to start with it will grow with each molt.

Temperament and Tankmates

Fiddler Crab on a Muddy Substrate
Fiddler Crab on a Muddy Substrate

Often these freshwater crabs are mistaken as being excellent companions in a community aquarium because of their quirky personalities. However there’s more to these feisty crabs than meets the eye. Improper tank mates can lead to harm for both species involved.

Are fiddler crabs aggressive?

As far as other fiddler crabs go there won’t be much aggression between those of the same species. However, males can become territorial which can lead to disputes where a male loses a claw.

What fish can live with fiddler crab?

It is recommended to choose tank mates where the fish are small enough to not be tempted to eat your fiddler crab. However, it is also important to find tank mates that are fast swimmers and can outdistance your fiddler crab if they decide the fish is encroaching on their territory.

Top 5 tank mates

  1. Other fiddler Crab-the best tank mates for this species is another fiddler crab. They enjoy having company and you can keep 2 per 10 gallons.
  2. Mollies-some success has been reported with this fish as they are fairly peaceful and fast swimmers.
  3. Guppies-some success has been reported with guppies as they are fast swimmers and tend to stay out of the bottom third of the tank.
  4. Danios-some success has been reported with danios as they are fast swimmers and are unlikely to choose your fiddler crab as a snack danios .
  5. Cherry Shrimp – another crustacean, they will likely leave your fiddler crab alone and help keep your tank clean.

Tank mates to avoid

  1. Other crabs-like previously mentioned, fiddler’s are very territorial and will not appreciate sharing the bottom of the aquarium with others, like the red claw crab.
  2. Pufferfish-puffers can be bullies when it comes to food, especially to small invertebrates
  3. Gobies-as crabs commonly bring diseases into aquariums without proper quarantining and this small fish is particularly susceptible to them it is recommended to avoid housing them together. If your heart is set on this fish be sure to quarantine your crab in separate tanks for at least a month.
  4. Mayan Cichlid-a commonly known aggressive individual that will likely bully your crabs.
  5. Siamese tigerfish-this fish requires an extremely large tank or else you risk aggression.Unless you are planning for a large brackish setup do not house them with your fiddler crab.

Tank Requirements

An Aquarium With Shallow Water
An Aquarium With Shallow Water

Fiddler crabs are fairly easy to keep and are a popular seller from fish stores due to their hardness and low maintenance.

Water Parameters

Tank Size10 gallons
Water TypeBrackish water
Water Temperature75-85
Water pH8.0-8.3
Water Hardness12-30 dKH
Salinity1.005-1.08

Tank setup:

What kind of Substrate to use?

Choosing the correct substrate for your fiddler is extremely important when it comes to their happiness and health. Not only do they need brackish water, they also need an artificial shoreline in their tank to encourage digging burrows and other natural behaviors.

Sand is the best substrate as it will allow the fiddler crabs to burrow and scavenge, and it is easy to form an artificial shoreline by piling more sand on one side of the tank until it’s just above the water level.

TIP

Choose sand over gravel as it is easier for your crab to dig burrows in. Mud can also make a good substrate and is what is present in their native habitat but can be unappealing for aquarium life.

Should I have a filter?

Choosing the right filter is another important part of keeping fiddler crabs as they are very dirty. An unclean or unmaintained tank can lead to a plethora of health problems and unhappy fiddler crabs.

What’s the point of a Pump?

This species enjoys a tank that is well circulated leading to your fiddler crabs having an easier time breathing air. As your filter will be internal (read more below!) it is necessary to have a pump or air bladder to create this circulation as the filter output will not.

Is a Water heater necessary?

It is absolutely necessary to have a water heater in your aquarium as most species of fiddler crabs are from a warmer environment. Having incorrect water temperature can lead to many health problems down the road and a shortened lifespan.

What kind of lighting to use?

These crabs are not picky when it comes to lighting, however they will likely be more active at night, especially the sand fiddler crab.

What kind of water do fiddler crabs need?

Fiddler crabs require brackish water, however they can survive in waters with low salinity and are often referred to as fresh water crabs.

Land water ratio

Unlike other crabs fiddler crabs only need water that is a few inches deep to thrive. They do not live in deep ocean waters and prefer the upper water column and shoreline. It is not necessary to have a large area of land in your tank, but be sure to provide enough dry area that your fiddle crab can burrow in the sand without being in the way of other crabs. A good rule of thumb is to have 10% of your tank be above water. In a 10 gallon tank the land area should take up roughly the same amount of space as 1 gallon of water.

RECOMMENDATION

Check out this article on paludariums to help you design your tank.

Avoid hang-on-back filters

It is essential that you avoid a filtration system that requires a hang on back filter. Fiddler crabs are well known for using filters to escape their enclosure. Instead, use a hang on back or canister filter and a tight fitting lid on your aquarium to make sure that your crabs stay where they belong.

Diet and Health

Fiddler Crab Burrowing On Substrate
Fiddler Crab Burrowing On Substrate

One of the easiest aspects of care for fiddler crabs is their diet because they eat almost anything! That doesn’t mean they should be given everything, instead owners should choose their diet carefully to ensure they are fed high quality food to help prevent disease and promote growth.

What do fiddler crabs eat?

Fiddler crabs are omnivores and scavengers, meaning that in the wild they eat a wide range of food that is available to them. The fiddler crab mostly finds its own food by digging a burrow and sifting through the sand with its mouth. As it digs you will see it spitting out pieces of sand that have been discarded.

Their natural diet includes fish eggs, kelp, seaweed, daphnia, algae, and tiny crustaceans.

What to feed a fiddler crab?

In your aquarium you should strive to feed your fiddler crab as close to a natural diet as possible. Options can include brine shrimp, daphnia, mosquito larvae, insect eggs, algae wafers, and vegetable matter. There are also a wide variety of commercial dry food that have been developed specifically for crabs and contains vitamins and minerals such as calcium to keep their shell strong.

FUN FACT

Fiddler crabs will even eat their old molts.

How often do you feed fiddler crab?

Feed your fiddler carbs and any additional crab once a day. They are messy eaters and will likely leave excess food and other organic matter along your tank floor. To keep your tank clean, get in the habit of removing this excess daily.

How much to feed a fiddler crab?

As fiddler crabs are scavengers and like to sift through the substrate to find their food you can’t rely on the 3 minute rule that we suggest for most other fish. Instead aim to feed your fiddler crab however much food they can eat over the span of an hour.

Common diseases of fiddler crab?

There are no species specific diseases for the fiddler crab, however poor health can be caused by bad tank maintenance practices and unhealthy living conditions. The most common ailments are bacteria, or fungal infections of the shell.

The best treatment for crab diseases is prevention. Be sure to establish a regular tank cleaning schedule which includes checking the water parameters, cleaning the filter, and siphoning the tank. Additionally, you should be sure that you are mixing the correct amount of freshwater and brackish water to obtain the correct salinity range for your crabs.

How long do fiddler crabs live?

Fiddler crabs live to be two to three years old under ideal living conditions.

Breeding

A fiddler crab brandishing its giant claw
A Fiddler Crab Brandishing Its Giant Claw

Fiddler crabs mate and send their larvae to deep ocean waters to develop, white impossible to recreate in captivity, their mating dance is entertaining and interesting to watch.

Can you breed a fiddler crab?

There is no way to recreate the conditions needed for breeding fiddler crabs, while the female might lay eggs and go through the process of mating rituals with the male the match will not work.

How to breed a fiddler crab?

While successfully breeding fiddler crabs is impossible the signs of mating can be easily recognized. The major claw that male crabs have is mate based, and it is proven that males with larger claws that wave them faster will have an increased chance of female mate choice. The logic behind this being that those with a more oversized claw are likely older meaning that they are good at surviving, and they have a bigger burrow for the female crab to lay her brood in.

Interestingly, each fiddler crab species has a slightly different wave pattern and wave speed of the enlarged claw.

What do fiddler crab eggs look like?

It’s unlikely you’ll see fiddler crab eggs as the females lay them in the males burrow. However, if you do manage to catch a glimpse you’ll notice that they are opaque and very small. Once the baby crabs begin to develop they will turn brown. The female can carry thousands of eggs under her carapace at once.

Fiddler crab FAQS

Why do fiddler crabs have a big claw?

The oversized claw that male fiddler crabs have is mainly mate based but is also used to demonstrate fighting ability. As the fiddler crab is very territorial you’ll notice it scurrying around waving its claw at any fish or crab that dares enter its territory.

When it’s time to mate your male fiddler crab will wave its claw and use it to drum to attract the female fiddler crab. The female is the one in charge and will decide what male she wants to mate with if there are multiple.

Do fiddler crabs like to be held?

No, holding your fiddler crab will likely stress it out and it will prefer to be allowed to stay on the substrate where it can burrow and hide in the mud or sand if it’s scared.

Can fiddler crabs swim to the surface?

As fiddler crabs should only be kept in water that is no more than a few inches deep they can technically”swim”to the surface. Though the action more resembles them propelling themselves through the water with their claws. More often they can be seen scurrying along the slope to the shore or back into the water.

Do fiddler crabs escape?

Yes, the fiddler crab is a well known escape artist and will use anything in their aquarium to climb out of the tank if possible. It is necessary to have an internal filter and a tight fitting lid for these crabs.

TIP

When feeding your crabs be sure to secure the lid before leaving the feeding session.

Are fiddler crabs aggressive?

While the fiddler crab is very territorial, unless there is another male crab encroaching on its territory it will not turn aggressive. You will notice your crab waving its claw at any passing fish, but fish tank mates should include those that are fast enough to swim past the claws with no damage.

What happens when a fiddler crab loses its claw?

When a fiddler crab loses one of its claws it will begin the process of growing it back during its next molt. The lost claws will be small when it initially grows back but will continue to get larger each molting cycle.

FUN FACT

If your fiddler crab has lost multiple claws or legs it will grow them back one at a time. This is because regrowing an appendage costs a lot of energy.

Is the fiddler crab for you?

In short, if you’re looking for a low maintenance and highly entertaining member for your aquarium you should consider a fiddler crab for your next purchase.

Conclusion

Fiddler crabs are great for beginner aquarists that are just starting to get their feet (or fins!) under them. With a filter, water pump, heater, and well-varied diet, you should be set to keep one of these fantastic creatures. Plus, with hundreds of subspecies to choose from, you’re sure to find the fiddler crab that’s the perfect fit for you!

Featured Image – Thai National Parks, CC BY-SA 2.0, via Wikimedia Commons
(1) Thai National Parks, CC BY-SA 2.0, via Wikimedia Commons

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