Complete Guide To The Red Claw Crab

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Looking to add some vibrant color to your tank, or are you just dipping your toes into the hobby? Either way, getting a few freshwater crabs is a great place to start.

Red claw crabs, in particular, are rather easy pets to care for, making them ideal for even novice aquarium enthusiasts.

red crab aquarium
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What can you expect from these interesting pets? Do they require special care? What is mandatory for their habitat? Can they play well with others?

To help you make the best decision for your aquarium, we’ll break down all of that and more. Let’s dive into what red claw crabs are like, how to build a proper red claw crab habitat, and how to care for these cool critters.

What Is The Red Claw Crab?

The red claw crab—also known as the Thai crab, the mini crab, the red crab, perisesarma bidens, sesarma bidens, or (pseudo)sesarma moeschi—is a crustacean species typically found in the Indo-Pacific region from Zanzibar to Japan and Fiji in mangrove swamps.

Usually, these areas are near rivers that flow out to the sea, which creates a unique mix of freshwater and salt water. Red claw crabs live in shallow, tropical waters with beds of fine sand.

These crabs are best known for their small size and vibrant red color, making them a fast favorite in the world pet trade.

They have a leg span of up to four inches (or ten centimeters) and the length of their carapace, or top shell, is usually no more than two inches (or five centimeters) at the most – hence their nickname, “the mini crab.”

Male red claw crabs have larger claws than their female counterparts, and they tend to be brighter in color, too. The underside of their shells is also pointier, whereas a females’ underside is rounder.

There is currently no data available on the average or maximum lifespan for this species in the wild. However, red claw crabs typically live for two or three years in an aquarium if they are properly cared for.

Most red claw crabs can easily be purchased online or at your local fish store. These crabs will range anywhere between $2 to $5 at the most, which makes them one of the most affordable and accessible pets you can own!

Red Claw Crab Care

While red claw crabs are quite easy to manage, unfortunately, many websites and aquarium stores often spread misinformation about their care, leading to some disastrous results.

Let’s take a look at the proper way to set up a red crab aquarium, as well as one of the most important questions: “What do red claw crabs eat?”

Perisesarma bidens
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Red Claw Crab Tank Set Up

Most pet websites and employees at aquarium stores will tell you that red claw crabs are best kept in freshwater community aquariums. However, their ideal habitat is actually a single-species, low-end, brackish paludarium.

A paludarium is basically a type of vivarium, or enclosed living area like a tank, which uses both aquatic and land elements to simulate its natural environment.

This means that your tank needs to contain both water and a piece of dry, sandy land for your crabs to properly thrive.

Red claw crabs are not fully aquatic beings, even if many other hobbyists may say otherwise! Access to land is nearly as vital to their health as food.

Water Conditions

Red claw crabs can survive in freshwater, but they actually prefer to settle in brackish water, which is basically a combination of marine salt and freshwater.

To create the perfect blend of salt and water, simply mix one to two tablespoons of marine salt per gallon of freshwater into your tank. It’s wise to mix the salt into the water in a bucket before pouring it into your tank.

Never pour the salt directly into the freshwater while your crabs are still in it! The shock to their system may lead to health problems – or even death.

Tank Temperature and Water pH

Remember to keep the water temperature anywhere between 75 to 80 degrees Fahrenheit. The pH should always remain somewhere around 7.5 to 8.5 as well.

Changing the Water

Be sure to invest in a tank that holds a minimum of 10 gallons of water. You should also give your tank a weekly 10 percent water change to keep their environment fresh and clean.

Of course, filters can help with this, but make sure that the openings to said filter are small; otherwise, your crabs may accidentally get swept up inside it.

Land and Secure Hiding Places

The rest of your tank should be dedicated to building an appropriate, sandy substrate that allows for easy foraging.

red claw crab tank mates
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It should also facilitate the crabs’ instinctual burrowing habits. If you’re lucky enough to catch them, you may even see their natural scavenging behavior throughout the day.

You should also give your crabs several hiding places, which they can use for molting or other activities. This can easily be done by supplying the tank with driftwood, aquarium décor, and/or aquatic plants. These plants can be real or made of plastic or silk.

Just keep in mind that you should not place any of your decorations in a way that allows your crabs to reach the top of your tank.

Red claw crabs are great at climbing and have proven themselves to be crafty escape artists. If the lid to your tank is not tightly fitted or fully sealed, or they find some other means to crawl out of their aquarium, then their escape will quickly spell tragedy.

Red claw crabs tend to dehydrate fairly quickly, so if they cannot get back to their tank and are left to wander around without water, they will die.

To prevent this, always be sure to keep your aquarium’s water line at least a few inches below the rim of the tank. Also, ensure that any openings your crabs can fit through are sealed tight.

This video goes into more detail on the set up of a red crab aquarium.

Red Claw Crab Food

While red claw crabs can and will eagerly hunt for their food, they are not very strict carnivores. Rather, they are opportunistic omnivores that readily accept almost any kind of food.

These include things like shrimp pellets; fish flakes; brine shrimp; bloodworms; blanched vegetables such as spinach, peas, or other leafy greens; commercial crab food; algae pellets; and even small pieces of uncooked fish.

A good diet for red claw crabs consists of many vegetables with some protein. If you want to treat your crabs or encourage exercise, you can also feed them live bait.

Red Claw Crab Molting

It is important for your tank to have many hiding places, as it is crucial for this species’ molting stages.

Crabs and other crustaceans do not grow in a linear fashion like most other animals. They have a hard outer shell that does not grow along with them, and so, in order to maintain their growth, they must then shed these shells in a process called molting.

This process can take them several weeks to complete, making a cozy hiding place all the more vital for their growth.

A day before its molting process begins, the crab starts to absorb the water around it. This helps the old shell to expand and come apart at a special seam that runs around its whole body.

The carapace then opens like a lid. The crab pushes and compresses all of its appendages repeatedly to remove the rest of its old shell. This process usually takes about 15 minutes.

Once the easy part is over, the crab then spends the next few weeks gradually retracting all of its body parts from the outer shell, a few millimeters at a time, all while secreting a new shell beneath the old one.

When a crab molts its old shell off, it removes all its legs, its eyestalks, its antennae, all its mouthparts, and its gills in the process. It also leaves behind its esophagus, its entire stomach lining, and even the last half inch of its intestine in the old shell. As such, they must make entirely new organs in this process as well.

Crabs will often participate in a population molt. This means that they will all start to molt at the same time. If you notice what looks like a dead crab hidden or floating about your tank, but know for sure that all your crabs are alive and well, then what you’re looking at is a cast-off crab exoskeleton instead.

After it is done molting, your crab will be full of water, making them very soft and vulnerable to predators. In what is called the intermolt period, the water is soon replaced by protein and their new shell hardens up within just a few days. The shell will then become extremely hard after a month.

Molting also helps crabs to get rid of parasites, barnacles, and other parasitic animals growing on the shell in one fell swoop. Finally, it helps them get rid of any clingy bacteria that degrade the chitin in the exoskeleton.

red claw crab care
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Red Claw Crab Tank Mates

Red claw crabs tend to be very aggressive and territorial, so it’s best to keep them in a single-species tank.

Decent Matches

If you must house them with other types of fish, be sure that they are a non-aggressive, mid-to-top dwelling, or fast-swimming species, such as most tetras, guppies, and mollies.

Due to their opportunistic hunting tendencies, red claw crabs will attack and eat any of slow, sick, or bottom-dwelling fish.

Any potential tank mates should be able to tolerate similar water and environmental conditions as well.

Bad Matches

The primary predators of the red claw crab include the black croaker, the black and yellow rockfish, the kelp rockfish, the copper rockfish, sculpins, the lingcod, the sea otter, the cabezon, and the East Pacific red octopus.

As such, do not house these crabs in tanks that already hold one or more of these species of fish (or mammal, in the case of the sea otter).

Crabs with Crabs

When setting up a single-species tank, however, keep in mind that you should not house multiple males together if you can help it.

Male red claw crabs can become quite territorial of their space, especially during mating season. If a male encounters another male, they will often get into brutal fights that can sometimes result in serious injuries or even death.

These crabs do not usually like anything coming near them, whether it’s a fish or a fellow crab. They will usually raise their claws to intimidate intruders, and will even pinch them if they dare get too close.

Some people report their crabs getting used to them after a while, but just keep in mind: they will not hesitate to pinch you if you ever have to handle them for whatever reason. When they feel threatened or annoyed, they don’t mind acting on that.

It may help to provide your crabs with multiple hiding places and territories within a large aquarium. Just be sure not to put too many crabs in one tank. An overcrowded tank can stress your crabs out, leading to disease, numerous territorial fights, and other issues.

If you get a 23.5-inch paludarium, placing one male with two or three females should work out well for both you and the crabs.

red claw crab tank mates

Mating Red Claw Crabs

Red claw crab mating will occur seasonally throughout the year.

Typically, the average brood per year is 3.5, with females reproducing for one to two months per clutch. They will often take short periods of rest in between these seasons, but not to care for their babies.

Many young crabs do not get parental care while they grow up; they often have to feed on algae and other microorganisms to survive.

As you can imagine, raising a successful brood of baby red claw crabs is almost impossible in a man-made tank setup.

Here’s a video with more information on red claw crabs.


The red claw crab is a feisty but simple pet that is fairly easy to care for.

Both novice aquarium enthusiasts and more seasoned experts alike will find this vibrant species a fun and interesting addition to any of their tanks.

Do you have experience caring for red claw crabs?

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