Red Claw Crab Ultimate Guide: A Marvelous Mangrove Crab

The Red Claw Crab is a fascinating little crustacean that has gained popularity in recent years.

They have gained popularity because of their wonderful appearance and intelligence.

Red Claw Crabs are very entertaining to watch and are quite different from what you might be familiar with. You will love watching them scuttle around and redecorate their home.

It is not difficult to care for one of these tiny crabs but they do need a brackish paludarium.

Keep reading to learn all you need to create the best home for a Red Claw Crab…

Red Claw Crab 101

Perisesarma bidens

The Red Claw Crab (Perisesarma bidens) is a tropical crustacean from the mangrove swamps of the Indo-Pacific.

They are also known as the Mangrove Crab, Thai Crab and Mini Crab.

Red Claw Crabs come from the family Sesarmidae and can be found everywhere from the eastern shores of Africa to the Fijian Islands.

This tiny crab only grows up to 2.5 inches inches long so they are a similar size to most aquarium shrimp.

While they make a fantastic addition to biotopes, they are not good in community tanks. Their shy and sensitive nature makes them quick to attack when they feel threatened. These small crabs are a common sight at most pet shops and they are usually sold in the freshwater invertebrate section. However, they are actually a brackish invertebrate.

Expect to pay around $3-$5 per crab.

Key Facts:

  • Experience Required: Brackish tanks.
  • Nicknames: Mangrove Crab, Thai Crab, Mini Crab.
  • Color Forms: Red.
  • Size: 2-2.5 inches.
  • Tank Size: Minimum 10+ gallon.
  • Tank Temperature: 75°F-80°F.
Pros

  • Fantastic starter pet for brackish tanks.
  • Affordable.
  • Helps clean up waste in the tank.
  • Attractive and decorative red color.
Cons

  • Aggressive to fish and other invertebrates.
  • Very skilled escape artist.
  • Destroys plants and décor.
  • Dehydrates and dries out easily.

Red Claw Crab Care Guide

Red Claw Crabs are very susceptible to dehydration.

Because of this you must give them a moist environment with regular access to a pool of water to keep their lungs from drying out.

Any crab that makes their way out of the tank is at risk of desiccating in the dry air outside. This is why it is so important to cover the tank with a hood.

Exposure to bright lights or a sudden increase in temperature can also cause them to dry out.

Another thing to remember is how toxic different metals can be for crustaceans. Copper, zinc and other metals that can be found in fertilizers and medications are deadly. Thankfully it is very unlikely that metals will be introduced to a tank with no plants and fish. But if your paludarium does include fish then you will need to find metal-free medication for them.

The final care item to be aware of is molting.

Crabs shed their exoskeletons as they grow and adult crabs continue to molt every month. While they are molting they will hide out.

Molting can take at least 2 weeks to complete and you should never disturb or distress your Crab while they are molting.

Diet

These little crabs are voracious scavengers that eat just about anything they can get their claws on.

In the wild they will eat detritus, worms, snails, shrimp and even small fish.

They will also munch on plants and algae.

Because of this they make very effective tank cleaners and eat up all the scraps that are left behind by their tank mates.

In an aquarium you can feed them flakes made for shrimp. But their favorite foods are live foods that they can hunt.

Bloodworms, ghost shrimp, snails and tiny feeder minnows all make excellent snacks when given either live or frozen.

They will occasionally graze on the algae that grows in your tank but this is uncommon.

Since greenery is just as important as protein you can also feed them leaves of Anubias, Java Ferns or Waterweeds. Garden vegetables and fruits also make an excellent treat.

Here are all of the foods that Red Claw Crabs will love:

  • Shrimp flakes
  • Bloodworms
  • Grass Shrimp
  • Ghost Shrimp
  • Feeder fish
  • Amphipods
  • Algae flake supplement
  • Algae
  • Spinach
  • Lettuce
  • Cucumber
  • Peas
  • Zucchini
  • Mango
  • Papaya
  • Banana

Crabs usually come out at night and just before sunrise to scavenge, so these are the best feeding times. They will only need to be fed about 3 times a week and will find food on their own most of the time.

Behavior

This crab is easily scared and spends most of their time hiding.

However this does not mean that they have a passive personality. They are well known for their aggression and when a threat is detected they will warn the potential attacker by lifting their claws.

If the intruder backs away then the crab will simply scurry off. If the intruder stays then they will be on the receiving end of a nasty pinch.

When you spot your crab they will usually be basking on a rock or hiding under a log. You might go an entire day without seeing them until they come out after sundown to scavenge. They will scavenge in the substrate and scurry in and out of the shallow areas of the water.

Red Claws also love to redecorate their tanks and this is often at the expense of your decorations and plants.

Are Red Claw Crabs Aggressive?

It is easy to underestimate these crabs by their size.

However these feisty little critters do not get along well with others.

They do not realize how small they are and will often go after much larger fish and invertebrates that get in their way. While it is possible to keep this critter in a limited community it is much safer to keep them on their own.

Red Claw Crab

Habitat and Aquarium Set Up

This crab is native to mangrove swamps where the river meets the sea.

In these areas there is a mix of different salinities from the sea and the freshwater rivers. Red Claw Crabs are therefore very adapted to these transient saline conditions where the water is never too fresh or too salty at any given time.

They take shelter under rocks and logs, or in the massive roots of the mangrove trees. You can also find them burrowed in the sand or the mud.

Unlike other freshwater crustaceans they spend most of their time on land rather than in water. This means that they will require both land and water in their tanks.

Aquarium Conditions

These Crabs can survive temperatures between 70-85°F, but 75-80°F is optimum.

The size of the tank should be at least 10 gallons and must include both terrestrial and aquatic sections. The pH should range from 7.0-8.5, and the hardness should be 18-20 dGH.

You will need an aquarium heater for the water and a heat lamp for your built-in shore. If possible you should purchase a heater specifically designed for a paludarium. You will also need a specialized filter for a paludarium as regular internal filters can be quite dangerous for small invertebrates.

The water levels in your tank should be low and very shallow. There is no need to add any depth to the water unless you are keeping fish as well. Soft sand or mud is the safest and easiest type of substrate for a crab to burrow in. It also holds water and retains moisture very well.

Substrate can also have rocks, logs, and other good places to hide. Just remember that your decorations should not be tall enough to allow the Crab to climb to the surface.

Light intensity should be low enough to keep both the Crab and the environment from desiccating. Use a full spectrum aquarium light turned down to a low intensity.

It is better to leave plants out of this particular tank as they will be uprooted or eaten. But you can try to include a single Java Fern or Anubias if you really want plants.

Tank Parameter Requirement
Minimum Tank Size 10 Gallons
Tank Type Brackish paludarium
Temperature 75-80°F
pH 7.0-8.5
Hardness 18-20 dGH
Flow None
Substrate Soft sand

What Size Aquarium Do They Need?

You will need at least a 10 gallon aquarium to keep Red Claw Crabs.

Add an additional 5 gallons for each new crab you add.

Red Claw Crab Appearance

Red Claw Crabs are much smaller than most other aquariums crabs.

The largest individuals grow to about 2.5 inches with the males being larger than females.

Just like all other arthropods the crab’s anatomy is split up into different segments.

The body is divided into an abdomen and a fused head and thorax which is protected by a hard shell called the carapace. For the easiest way to tell the gender of your crab, turn them over and look at their abdomen. The exoskeleton on the male’s abdomen is narrow and slightly pointed, while the female’s is wide and round.

Males also have a larger carapace and claws.

Their characteristic red claws stand out against an otherwise drab brown colored body. The claws usually have bright yellow tips too.

Crabs are decapods with 5 pairs of legs.

The first pair of legs are called the chelipeds and these end in the claws. The claws are used for digging, grabbing food, and defense against potential predators.

Behind the chelipeds are 3 pairs of walking legs, or pereopods. These give way to a pair of legs that are modified for maneuvering in water.

Two small beady eyes protrude outward from the cephalothorax. They can use these to see from every direction while staying in one spot.

History and First Sighting

Perisesarma bidens were first discovered in Japan in 1835.

At the time it was believed they were endemic to Asia until other populations were found in the 20th century.

Throughout most of their history they were used as bait for fishing. It was not until the 1970s that this species was commonly studied in laboratories to determine their role in mangrove swamp ecosystems.

Crabs became popular as aquarium pets in the late 90s and early 2000s, which is when this crab was introduced as an ornamental invertebrate.

Aquarium keepers instantly fell in love with their beautiful colors, intelligence and personality. However they were quite taken aback by their specialized water conditions and aggression.

Even with all of its flaws, it is well loved in the aquarium community.

These days you can find this crab in just about any pet store. Just make sure not to confuse them with Perisesarma guttatum who are also known as the Mangrove Crab.

Tank Mates

These angry Crabs do not get along very well with others.

Their aggressive nature makes it a challenge to find suitable tank mates for them.

Tank mates should only be added when there is enough space for them not to disturb the Red Claw Crab. They must also have a peaceful temperament and be able to tolerate brackish conditions.

Finding suitable tank mates for this critter is largely a game of trial and error.

You might have some success pairing them with Molly Fish and Gobies.

Dragon, Neon and Knight Gobies in particular are both strong and quick enough to stand up to a bit of bullying.

Guppies are also worth a try.

Flagfish and other small Killies tend to work out well too.

Fish that travel in schools (like Neon Tetras) are much safer than those that swim alone.

As for what to avoid the list is numerous.

Puffers, Archerfish and other predatory fish are at the top.

Slow moving bottom dwelling fish are also out of the question. These include the Bumblebee Goby and any species of loach.

Snails, shrimp, and other small invertebrates should also be avoided as they will be eaten.

Your Crab’s terrestrial setup should also be free of frogs and lizards.

Can Red Claw Crabs Live With Fish?

A Red Claw Crabs compatibility with different fish is mainly down to luck. More often than not it is just not worth the risk to place any fish in your Red Claw’s habitat.

Any fish you do keep with them should be quick enough to be able to get away in a (literal) pinch.

All fish should occupy the levels of the Paludarium that the Crab cannot reach. They should also be compatible with a brackish water environment.

Keeping Red Claw Crabs Together

These Crabs can only be kept in small breeding groups (1 male and 2 females).

Any other arrangement is risky.

If you keep multiple males together then they will kill each other in the fight for dominance over the females.

Beginners should keep a single Crab on their own.

Breeding Red Claw Crabs

Red Claw Crab are extremely difficult to breed in home aquariums.

Breeding should only be attempted by experienced invertebrate keepers.

You will need a small group of 1 male and 2 females.

The first thing you will need to do is simulate the conditions of a natural breeding season – this means raising the temperature above 80°F. Once the right conditions are met, one of the females will select the male for breeding.

During this time you should also add more protein to your group’s diet. Feed them live prey at least 3 times per day.

Males mate by climbing on top of an upside-down female. Once the eggs are gestated you will be able to see them carried in the female’s abdomen. The female may carry hundreds of eggs at a time but very few of these will survive.

After 20 days the eggs will hatch into microscopic zoea larvae.

This stage lasts for about 2 weeks during which the larvae must find food completely on their own. At 2 weeks old they will grow into the megalopae stage of life. Megalopae can be fed larval brine shrimp and other microscopic larvae. Every 3 days they will undergo a molt into their next instar.

It will take about a month for your megalopae to grow into juvenile crabs. They will look much more like crabs now and settle into the substrate using their brand new walking legs.

From here until maturity, new molts will occur every 7 to 10 days.

Your crabs will reach full maturity in a little under 2 months.

Species Summary Table

Red Claw Crab
Other Common Names: Thai Crab, Mangrove Crab, Mini Crab
Scientific Name: Perisesarma bidens
Family Name: Sesarmidae
Distribution: East Africa to Fiji Islands
Size: 2-2.5 inches
Color: Red
Care Level: Intermediate
Temperament: Aggressive
Lifespan: 2 years
Minimum Tank Size: 10 gallons
Tank Mate Compatibility: Single species

Frequently Asked Questions

Can You Handle Red Clawed Crabs?

These Crabs are very skittish and do not like to be handled.

You should only handle your Crab when it is absolutely necessary. Even a tiny crab like this can pack quite a pinch, so you should never handle your crab from the front!

When cleaning your tank or moving a pregnant crab to a nursery, use your thumb and first two fingers to gently grasp it from behind. The crab may try to pinch you but it will not be able to reach behind.

If you do get pinched then place the crab back into the water and it will let go when wet!

Should You Keep The Red Claw Crab? (Summary)

The Red Claw Crab certainly makes one of the most interesting additions to an aquarium.

Their skittish and feisty personality makes them entertaining to keep.

They will need a brackish palladium which is a fairly unique setup within the aquarium hobby.

Because of this they are not the best community Crab and they should not be kept with other critters in most circumstances. There is just too much of a possibility for competition with tank mates.

However if you can give a Red Claw Crab the right home you will be rewarded with an enjoyable invertebrate.

Have you been more successful keeping this Crab at home?

Let us know in the comments section below…

David Thomas Author Bio Picture
David Thomas leads the team at Everything Fishkeeping as the Editor-in-Chief. David has been keeping fish since he was a child. In his first tank he kept goldfish and since then he has kept over 30 different species. Now he has 4 separate tanks and his favorite is a 100 gallon freshwater tank with a school of Rasboras, Tetras and Loaches.

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