Red claw crabs (Perisesarma bidens) are an interesting and attractive crab species that can be a great addition to your aquarium (paludarium). Have you been thinking about keeping and setting up a Red clawed crab tank, but you aren’t sure how to care for them? Then you’ve come to the right place. Below I have laid out a complete guide to keeping, caring, and breeding for this species of crab.
Red claw crabs are classic brackish water, mangrove crabs. They have a lot of character, personality, and can be a great addition to your home tank. The only rule here is that they are not fully aquatic. Red claw crabs can spend half of their time in land. This is absolutely crucial for their breathing.
In recent years, interest in alternative species in aquariums has increased considerably. Red claw crab is one of the most traded crab species. Unfortunately, a lot of retailers still continue to sell them as “freshwater crabs” or “aquatic crabs”.
Quick Notes about Red claw crab
|Name||Red claw crab|
||Mini Crab, theRed Crab, Grapsus bidens, Sesarma Moeschi|
|Scientific Name||Perisesarma bidens, formerly Sesarma bidens|
|Tank size (minimal)||10 gallons (~45 liters)|
|Size||10 cm (4 inches) across the leg span|
|Optimal Temperature||22 – 31°C (~70°F – 88°F)|
|Water type||Slightly Brackish (SG 1.005)|
|Optimal PH||7.2 – 8.5|
|Optimal GH||8 – 25|
|Optimal TDS||150 – 200 (100-300)|
|Nitrate||Less than 40 ppm|
|Life span||up to 2.5 years|
|Color Form||Shades of red, to flaming orange with brown spots|
Natural Habitat of Red Claw Crabs
Red claw crabs are also known as and sometimes sold under these names Perisesarma Bidens, Mini crab, or Sesarma Moeschi. This species of crab is native to Asia where they dwell and thrive in the shallow and warm coastal mangrove swamps. While they are mistaken for freshwater crabs and can survive in freshwater, they do their best in brackish water.
The shallow mangrove swamps where they are found often mix with the seawater, which raises the salinity. This is where the misconception that they are freshwater crabs comes from. In general, mangrove swamps are freshwater swamps and not brackish, but because the ones where Red claw crabs are found are along the coastline, the water will always have some salinity.
Red Claw Crabs Description
Red claw crabs vary in shades of red, to flaming orange. Their shells are covered in brown spots. The males tend to be brighter and more colorful than females. The tips of the claws will be a yellowish color, ranging in shade from pale to bright.
The carapace of an adult Red claw crab only grows to about 1.5 – 2 inches long (3.5 – 5 cm), with a leg span up to 4 inches (about 10 cm). They are smaller than most aquarium crab species. This is the reason they are sometimes known as Mini crabs.
Red claw crabs have two “teeth” (lat. bidēns – having two blades or teeth) on the lateral sides of the carapace.
Red claw crabs have a gill chamber (not lung). The gill chamber is located under the carapace near the first pair of walking legs. As long as their gills stay moist, they can be out of the water.
Interesting: Red claw crabs have special plates, that keep their gills moist by shutting the opening in the exoskeleton so that dry air cannot get in. Although they have a gill, they are still semi-aquatic and require fresh air as well.
Important: Do not put a Red claw crab in a tank that is filled up with water. They need a piece of land or a place log or a rock so they can reach the surface to breathe. Otherwise, they will drown.
Red Claw Crabs Lifespan
The average lifespan of Red claw crabs in captivity is about 2 years. However, some individuals do live longer. According to the studies, the lifespan of Red claw crabs in the wild is about 2.5 years.
Note: Biologists used composite growth curves as an indication of the longevity of carb.
Red Claw Crab Behavior
Red claw crabs are shy creatures. They are nocturnal and spend most of their time hiding. However, if you do see them exploring the tank, they will most often always be scavenging along the bottom. This can be an amusing sight to watch as they scurry along, searching the bottom for food.
They are excellent climbers and escape artists, not only are they skilled at avoiding predators, but they will also escape their tank if given the opportunity. They move quickly and can run, or walk with ease underwater.
Red claw crabs are territorial and very aggressive to each other. When they encounter a tank mate they will often raise their claws in a defensive manner that can quickly become offensive. A threatened Red claw crab will attack. Especially when the offender is a smaller tank mate.
Red claw crabs are fairly skilled hunters when needed, but they prefer to scavenge. They make small dens under aquarium decorations and plants, and will readily retreat to these caves if overly threatened, or scared. They will also stay hidden in these dens for multiple days while they molt.
Important: The level of aggression depends on the amount of space they have, and the number of hiding spots they have. Unfortunately, even a 10-gallon tank (45 liters) will not guarantee the piece.
Males will fight for territory and dominance because in the wild they have more than “10-gallons” of their territory. The female Red claw crabs are not that aggressive. They will usually chase each other away.
Keep in mind that Red claw crabs are very destructive. They will “redecorate” your tank to their liking.
Red Claw Crab Molting
Because they have an exoskeleton, Red claw crabs must molt in order to grow. The molting process itself usually lasts only a few minutes. However, they will need time to harden their new shells after that. Therefore, it is crucial to your crab survival that your tank has plenty of hiding spaces. They will choose one of these spaces as a safe retreat while they are vulnerable.
It takes weeks for a crab to prepare for molting. The day before a Red clawed crab begins to molt, it will stop eating and absorb the water. This allows the crab’s shell to essentially crack open around its body and the top lifts up. In this hobby, we call it a breaking point. It will then begin to remove itself from the old shell.
Note: Like any type of crabs and shrimp, Red claw crabs can regenerate pinchers (claws) or legs lost while fighting or protecting themselves. These lost limbs will regrow after two or more molts.
Once finished the cast off exoskeleton will resemble a fully intact, “dead” crab. So, if you see one hidden among the decorations in your tank, don’t panic. After molting it will take a while for your Red claw crab’s new skeleton to fully harden. During this time they are filled with water, extremely vulnerable, and prone to injury.
Tip: Do not remove the old exoskeleton. It contains a lot of calcium and your crab with gladly eat it later.
Sometimes the crabs can fail at molting (they cannot get out of their old shell). Unfortunately, once the molt starts to go bad, we cannot do anything for crabs or shrimp. All we can do is wait and hope for the best.
Red Claw Crabs – Male and Female Differences
Males and females can easily be distinguished in this species. According to the study, male Red claw crabs have a larger carapace (~20mm) than females (10 – 19 mm). Therefore, in general, males are bigger.
In addition, male Red claw crabs have larger, brighter claws and the underside of their shell will have an oblong or pointed appearance. In contrast, females will have smaller (about half that size), darker claws, and their underside will be rounded (wider and oval).
Feeding Your Red Claw Crabs
In their natural habitat, Red claw crabs are scavenging omnivores. This means they will eat just about anything, from algae and plant matter to small, slow-moving, or weak fish, shrimp. They will scavenge the bottom of the tank for scraps left behind by other creatures. Thus, they can be a part of the cleanup crew in your tank.
Many pre-made, sinking fish foods, like shrimp pellets, make a good main diet for Red claw crabs. You can find these pellets and other options at most fish stores.
Foods Red Claw Crab Will Enjoy
- Shrimp pellets
- Shrimp Granules
- Fish food (TetraMin® flakes, etc)
- Shrimp food (Hikari’s crustacean food like Hikari Shrimp Cuisine, Algae wafers, Brine shrimp, etc )
- Frozen blood worms
- Vegetables like spinach, peas, squash, leafy greens, etc.
As you can see, they will eat pretty much anything!
Do not forget that variety in food is always better because they will get different microelements necessary for them.
When you decide to give Red claw crabs vegetables, you need to do it the safe way. Read my article “How to Blanch Сucumbers and Zucchini for Shrimp, Snails and Fish the Right Way”.
Tip: Remove leftover food over 1 – 2 days old.
Like all invertebrates, Red claw crabs need calcium supplements to the water. I highly recommend reading my article “How to Supplement Shrimp and Snails with Calcium”.
Red Claw Crabs and Plants
Red claw crabs and plants are not compatible. They will eat, munch, cut, and uproot everything in your tank. Therefore, if you are planning to keep them with plants be ready for total destruction.
As I have just said, they eat a lot of vegetation. Nonetheless, even if you serve them lettuce, salads, cucumbers, zucchini, kale, etc. regularly. It will not prevent them from eating the plants too.
Red claw crabs are voracious vegetarian type eaters.
Keeping Red Claw Crabs
Red claw crabs do best in a tank (paludarium) that has been specifically set up for them or an existing tank that has been altered to meet their needs. It is very important to provide them with caves and rock crevices to hide. You will need at least (minimum) a 10-gallon tank for one of them. Potentially it might do for two of them, provided they are not both male, as males will fight.
Note: Despite their small size, Red claw crabs need a lot of space to be happy. Even a 10-gallon tank can barely replicate anything close to their natural habitat.
I know that some people keep them in 5-gallon tanks. I do not support it because it will constantly stress Red claw crabs.
Red Claw Crabs and Substrate
A sandy substrate (for example, Carib sea sand – Check the price on Amazon) is the best choice for the Red Clawed crabs.
I have heard so many times people saying that Red Clawed crabs need sand because gravel can break off the tips of their legs. Well, this is so wrong! It seems like somebody said it once and now almost everybody repeats this nonsense.
In reality, there is another explanation. Red Clawed crabs prefer sand because they are burrowers. So they are better equipped for this type of substrate. It replicates their natural environment. However, they also have a strong preference for natural refuges such as rock crevices, under and between boulders.
Tip: Choosing light-colored sand will create a nice contrast between your crabs and the tank floor.
Red Claw Crabs and Water/Land Ratio
Red claw crabs are not fully aquatic and thus need perches above the water line accessible to them. They have to come to the surface to breathe.
Aquarium driftwood and other perches made from natural material are easier for the crab to use and are also a good choice. You can set this up as a piece of driftwood sticking up out of the water. It is best if your crab has access to a dry, mounted perch as well. This perch should float on the water (mounted to the side of the tank) and have a dry sandy substrate. Having access to dry land is almost as important to the health of your crab as having air.
The water to land ratio should be at least 3 to 1. They will spend almost 50% of their time in land. This is very important especially if you have two of them. Because they are extremely territorial, if one crab claims the one small bit of land, the others may not be “allowed” out at all!
Red clawed crabs love more humid conditions.
Important: Last, but not least a tight-fitting aquarium lid is mandatory! Red claw crabs will escape if given the opportunity. Cover even the smallest of gaps. You will not believe how good these little Harry Houdini are at escaping. Once outside the tank, they will die of dehydration within hours.
Red Claw Crabs and Heater
Often people ask – do I need a heater for Red clawed crabs? The answer is simple.
Red claw crabs come from a temperate, tropical region. They need water temperatures that stay between 22 – 27°C (~70°F – 80°F) at all times, with no drastic jumps from high to low ends. Therefore, if your house is always that temperature even overnight then no, if not then yes, you need one.
Red Claw Crabs and Lighting
There are no special requirements for lighting. Everything depends on the plants in your tank. For example, a simple LED lighting just to help the plants grow will be good enough.
Red Claw Crabs and Filtration
Red clawed crabs need a filter. Of course, I know that some people manage to keep them even without a filter. In my opinion, it is a bad idea and torture for the crab or any aquatic creature.
The type of filter you can use depends on your water level in the first place. Unlike shrimp tank setups (you can read my article “The Best Filtration System for Breeding Shrimp”), these types of setups are most easily filtered with canister, or in-tank filtration.
For example, right now there are Terrarium and Paludarium filters for aquatic animals (links to check the price on Amazon).
Note: Sponge and Hang On Back Filters do not work well with lowered water levels.
Red Claw Crabs and Water Requirements
While they can survive in freshwater, or saltwater, slightly brackish water with a pH level of 7.2 – 8.5 is perfect for them. Red claw crabs prefer quite hard water. They do come from Asian Mangroves and Estuaries after all.
You will need something to test the salinity of the water and some good salt. I would advise using Instant ocean marine salt (link to check the price on Amazon) for brackish setup. You will also need a Therm/ Hydrometer (link to check the price on Amazon).
The range of “saltiness” varies greatly between different crab species. Red claw crabs require only slightly brackish water. Brackish water with SG. of 1.005 will suit Red claw crab very well. Basically, it is a little less than a teaspoon per gallon of water.
Note: Full seawater is 35 gram salt per liter. So, what we are making is about 1/6 normal seawater salinity.
When adding the brackish water to your Red claw crab aquarium it is recommended that you mix the water thoroughly in a bucket first. Never add salt directly to freshwater already housing Red claw crabs, the shock can kill/hurt them.
Important: Never use table salt in an aquarium.
Note: They can live in freshwater but it will greatly decrease their lifespan (from 2.5 years in brackish water to a few months (at most) in freshwater).
Water changes should be done regularly.
Tank Equipment (examples with links to check the price on Amazon)
Breeding Red Claw Crabs
In their natural habitat, Red claw crabs mate only from April until September. Females are known to be able to re-berry shortly after releasing their first batch of larvae and hence, each female can produce at least two brood a year (before the arrival of the cold season).
The mating rituals of this species are still unclear (if exist at all). Males just flip over females and pin them down.
Interesting fact: According to studies, the smallest ovigerous Red claw crab female was 8.7 mm, indicating that they reach sexual maturity at a relatively small size.
The incubation time of fertilized eggs takes 20 days. Baby red crabs begin their lives as larva, after hatching from eggs and receive no maternal care. Unfortunate babies may even become an easy meal for the Red clawed crab.
The time required for complete metamorphosis in the Red clawed crabs (under laboratory conditions) also varies greatly, ranging from – two weeks to more than one month (~36 days).
Therefore, it takes around 50 – 60 days for the babies to transform into Red clawed crabs (starting from brood incubation).
Red Claw Crabs Breeding Experiments
Unfortunately, successful mating is rare in tank set ups and it is almost impossible to rear baby Red clawed crabs. However, it is not completely unheard of.
If you want to test your skill sets and breed them, you will need to know some facts about them.
There are 4 stages of larvae + Megalopa stage (final stage of larvae – semi-transformed). Each stage lasts 3-6 days (depending on salinity and temperature). Megalopa stage lasts about 5-9 days (depending on salinity and temperature).
According to different studies, it is extremely important to pay attention to the salinity level. For example, in one of the experiments, the larvae were exposed to eight different salinities of 0, 5，10，15，20，25，30 and 35%.
In 0 and 5% Red clawed crabs larvae died within 12 hours after exposure without molting to the next stage. Thus, optimal salinity:
- for the first stage 20-30%，
- for the second and third stage 25-30%，
- for the fourth and megalopa stage 20-25%，
Therefore, in general, 25% is the optimal salinity for the complete larval development of Red clawed crabs larvae.
Feeding Red clawed crabs larvae – everyday biologists added newly hatched nauplii of the brine shrimp.
Note: You need a separate rearing tank for the larvae. The water must be also aerated and renewed 50% daily.
Red Claw Crabs Tankmates
Before putting a new Red claw crab in your tank, or putting a new tank mate in with your Red claw crab, you should take some things into consideration. These crabs are not social. When kept in captivity, they tend to cannibalize.
Male red claw crabs should never be kept together. They can be extremely aggressive towards each other. They will fight over territory and oftentimes the outcomes are deadly. However, you can house multiple females together with a single male.
Note: Many aquarists report that males absolutely can never get along. Even with a lot of space in the tank.
Fast swimming fish that prefer to live in the upper water levels of the tank make suitable tank mates for Red claw crabs. For example, your crabs will not bother Neon tetras, Guppies, Mollies unless they are sick and weak, then they become dinner.
Note: Red claw crabs are not active hunters. Their claws are cutter-shaped, which are more efficient for shredding leaf litter and picking up bits of stuff rather than catching things. Nonetheless, they are very good at killing their own kind. Therefore, the risk remains all the time that they do get the occasional fish or shrimp.
They may come out and hunt at night when the fish are sleeping near the bottom. Red claw crabs will try to eat whatever hits the ground near them.
Do Not Keep Red Claw Crabs With
Avoid housing Red claw crabs with slower-moving, bottom-feeding fish. They will likely become a meal for your Red claw crab at some point. In addition, of course, never house your Red claw crabs with fish that are big enough to eat them.
When choosing to house your crab with other species always be sure that water salinity and temperature requirements are similar. Never put freshwater fish into brackish water.
Do not keep Red claw crabs with a turtle in the same tank. The turtles will probably eat them eventually (It depends on the size of the turtle).
Do not put these crabs with dwarf frogs and snails. The crab can injure and kill it.
Dwarf Shrimp are also not good neighbors. Although, Red claw crabs will not be able to catch a healthy one. Your shrimp will be an easy meal during molting. Therefore, it is not advisable to keep them with any type of dwarf shrimp.
Do not keep Fiddler crabs and Red-Claws together. In most cases, Fiddlers will lose the fight, and the Red Claws will treat weak specimens as live food.
Basically, Red claw crabs do best in tanks with nothing but themselves inside.
Red claw crabs are feisty, but when cared for properly they can make an amazing pet, for expert, or novice aquarium enthusiasts alike.
Make sure to provide lots of hides, the proper diet and a good amount of brackish water that they will always have access too among other things and you will have a happy crab!