Crabs are one of the main arthropods that fit in well in an aquarium environment. For those who are interested in freshwater crabs, there are a whole lot of options but not everyone is aware of them. There’s more to this class of critter than just fiddler crabs.
So, let’s hop right in and take a look at our list of freshwater crabs. Well, give you some options to look at and the basics of their care so you don’t go in blind!
Contents
1. Fiddler Crab
Scientific Name: Uca spp.
Size: Up to 2”
Care Level: Easy
Special Care: Brackish Water, Ledge/Land Access
Fiddler crabs are one of the most popular freshwater crabs. They’re relatively small, common, and easy to care for. Fiddler crabs will eat just about anything and they do well in most types of tank provided they have a ledge to climb up on.
In the wild, these crabs often inhabit brackish lagoons. There they wander around scavenging in the sand in huge numbers. Their name comes from the large claw that male specimens have. This claw is almost comically large in comparison to the crab and useless for most purposes.
Instead, it’s used as a mating display. The male fiddler crab will climb to a high spot in the tank and “dance” while waving his large claw in the air. This impressive display of virility is meant to attract female fiddler crabs for mating purposes. The females can easily be distinguished since they only have two small claws.
The only caveat to their care is that fiddler crabs need brackish water. They will survive for a long time in freshwater but it will significantly shorten their lifespan. The water doesn’t need to have high salinity, enough aquarium salt for optimal health in animals like Mollies is perfect.
There are over a hundred species of the fiddler crab, and it’s hard to know which one you have in your tank if you’re not a crustacean taxonomist. General care is still the same overall, just try to pick out breeding pairs from the same batch of crabs to avoid problems with interspecies compatibility.
2. Red Claw Crab
Scientific Name: Perisesarma bidens
Size: 2”
Care Level: Easy
Special Care: Ledge/Land Access
The second most common variety of freshwater crab are the humble Red Claw Crabs. These small crabs are about the same size as fiddlers. Unlike fiddlers they have very large, burly claws for their size and they know how to use them. They’re a great option for a true freshwater tank but they’re not the easiest creature to deal with.
Not because they’re hard to keep alive. They’re quite easy to care for, especially since they’ll eat anything. The problems that arise are that these crabs can be dangerous to fish in the same aquarium. The males are also very territorial and will fight to the death over their feeding grounds.
They’ll also take a good chunk out of your finger if you’re not careful. Of all the small crabs I’ve dealt with they’re the most aggressive. Be careful working in a tank with these guys, those burly claws can open deceptively large. They’ll also snatch fish, shrimp, and other fauna if they can.
Red Claw Crabs do require a ledge of some sort to stay healthy. They’re not true aquatic crabs, although they’ll spend most of their time in the water. They’re best kept in a specimen tank or in a display tank with only top-level swimmers. Aside from the aggression, however, these are among the easiest crabs to care for.
3. Vampire Crab
Scientific Name: Geosesarma dennerle
Size: 2”
Care Level: Moderate
Special Care: Ledge/Land Access, Sand Substrate, Meaty Foods
The Vampire Crab is a strange species of freshwater crab. Uniquely beautiful, with bright yellow eyes and a deep purple shell, these crabs hit the scene with a big splash and then disappeared for a while about a decade ago. The problem for most people was keeping them alive, but one key tip can help keep yours thriving.
These crabs aren’t semi-aquatic… they’re semi-terrestrial. They need a lot of land and will preferentially spend their time there. A true paludarium is your best bet, especially if you opt to go with a slope of sand instead of a floating turtle dock as your land access. You want about 50% of the top level of the tank dry.
Vampire crabs like to burrow, so a sandy substrate is also a must. If you can manage these two small things then you’ll end up having an easy time caring for them. These are predatory crabs, so be careful what else goes in the tank. They share a similar aggression level to Red Claw Crabs, but are generally fine being placed together as a group.
You’ll also need to feed them frozen, meaty foods on a regular basis. These crabs aren’t really detrivores, although they will scavenge a bit.
Vampire crabs aren’t known very well to science, so there’s a lot of guesswork about their care. Indeed, vampire crabs were in tanks around the world before scientists got around to studying them. As such, take any information (including mine!) with a grain of salt. People can only speak from their experience with this species, there isn’t enough formal research to draw conclusions beyond what’s known to people who already keep them.
4. Panther Crab
Scientific Name: Parathelphusa pantherina
Size: 3”
Care Level: Easy
Special Care: n/a
The Panther Crab, or Parathelphusa pantherina, is a larger species of freshwater crab. While not the biggest available in the aquatic trade they get considerably bigger than species like Fiddlers and Vampire Crabs. They’re named for their spotted carapace, but their aggression levels could play a part as well.
Panther Crabs are fully aquatic. They live their entire lives under the surface of the water, never having to come onto land. There are very few species of freshwater crab where this is true. It makes them a good choice for tanks that need to remain sealed to prevent the escape of other animals.
Panther crabs are an endangered species, part of the IUCN’s red list. This isn’t due to the aquarium trade for once. Instead, it’s related to heavy nickel mining in the areas where they’re found in the wild. Since they can be bred in captivity (with some difficulty) they’re still available but it’s a good idea to make sure that yours have been captive bred.
Panther crabs eat everything, and they’ll shred plants. I’ve had luck with Anubias sp. kept alongside them but stem plants and anything with a rosette is at risk. That’s fine since you need to decorate the tank with driftwood or stone to give the Panther Crab a place to burrow as well. These pure aquatic crabs are a great choice for those looking for something a bit bigger than the usual crab choices.
5. Thai Micro Crab
Scientific Name: Limnopilos naiyanetr
Size: ½”
Care Level: Easy
Special Care: n/a
If I had to pick an absolute favorite freshwater crab, it would be the Thai Micro Crab. These tiny critters are easier to take care of than any other freshwater crab. They’re fully aquatic, scavengers, and are too small to do any damage to the vast majority of fish and arthropods. Indeed, they’re at a higher risk of being eaten than of killing any of your other animals.
These crabs hail from only one location, a specific river in Thailand. Unfortunately, they’ve proven to be very hard to breed in captivity so the majority of specimens are still wild-caught. This limits the market somewhat and can make them hard to find if you’re not willing to order them online.
These crabs are a bit odd in their behavior. They tend to sit motionless for long periods and only move when they’re actively scavenging. They’re small enough to be hard to observe most of the time, so it’s not much of a bother. They’re efficient cleaners of the bottom level of the tank.
These micro crabs are also plant-safe. I’ve kept them alongside Cherry Shrimp in nano tanks frequently, the two of them make for a good pair of cleaners. I would advise against keeping them with bottom dwellers, however, as boisterous but peaceful fish like Corydoras sp. will cause them a lot of stress.
6. Matano Crab
Scientific Name: Syntripsa matannensis
Size: 2 ½”
Care Level: Easy
Special Care: Meaty foods
The Matano Crab is another purple species, easily distinguished from the Vampire Crab since it lacks the bright eyes of the latter. These are fully aquatic crabs, able to spend their entire life in the water and remove the need for a ledge or paludarium. They’re a bit bigger than most freshwater crabs, between Fiddlers and Panther Crabs in size.
These crabs are natives of Lake Matano in Indonesia. They’re another species that’s been categorized on the IUCN red list. Breeding has proved difficult, so the majority of them come from their natural habitat which can raise ethical issues for the prospective keeper. I generally advise against keeping endangered species that are hard to breed, but you’re free to make your own choices.
These crabs are beautiful and active creatures. They can have some aggression issues with other crab species but aren’t as nasty as Red Claw Crabs in that regard. They tend to calm down once they feel they’ve established a territory rather than continuing to press on other creatures in the tank. That said, the males don’t like each other so keeping them separate is ideal.
These crabs are predatory, so make sure to feed them bloodworms, cubed beef heart, or other high-protein foods. This can also help improve their color. I get the feeling these crabs are here to stay, especially once the breeding issues are sorted by professionals. Other than their status on the IUCN list, keeping Matano Crabs is remarkably easy.
7. Rainbow Land Crab
Scientific Name: Cardisoma armatum
Size: 4”
Care Level: Moderate-Advanced
Special Care: Primarily Terrestrial, Sandy Substrate, Special Feeding
The Rainbow Land Crab is the biggest of the commonly available freshwater crab species. With legs, they can end up measuring over 6” from tip to tip! Calling them a freshwater species is the best kind of correct, it’s technically correct. These crabs require a small body of water to live but they’re primarily terrestrial.
Since these crabs spend most of their time on land, you should design the aquarium accordingly. Sand is necessary as well, the Rainbow Land Crab will spend much of its time burrowed during the day. These are nocturnal, like most crabs, but they tend to adapt to their owners’ schedule quickly.
The main problem with keeping them is the diet. Their diet should mainly consist of vegetables and leafy greens, with a high protein addition once per week. These crabs need a varied diet, so don’t be afraid to shake things up a little bit. Just make sure that everything is crab-safe before feedings.
These crabs can do a considerable amount of damage if you aren’t careful. Don’t let them get a hold on your fingers. Trust me, you’ll get a bit more than a pinch and lacerations don’t heal quickly. If you’re prepared to offer the special care it needs, however, this is a great option for a crab lover’s specimen tank.
8. Pom Pom Crab
Scientific Name: Ptychognathus barbatus
Size: 1 ½”
Care Level: Moderate-Advanced
Special Care: n/a
Pom Pom Crabs are tiny, rare crabs that have small tufts of hair on their claws. They’re usually a mottled yellow color. They’re among the smaller crabs available at the current time, topping out at 1 ½”. In my experience, they’re usually smaller than that by a bit, but they’re not quite as small as Thai Micro Crabs.
The Pom Pom Crab’s unique hairs can help you determine the sex of the creature. Males will have thick, bushy growths while females will usually only have a few stray hairs. This seems to indicate some function in their mating ritual, but they also catch particles for the crab to eat. They’re essentially a flashy lunch box.
Don’t confuse them with the saltwater crab with the same common name. They’re very different creatures. These Pom Pom Crabs tend to be very active, which is a rarity in the crab world. Many crabs don’t do much, especially during the day, but Pom Poms are quite active.
This is another species where hobbyists know as much or more than scientists. They just haven’t been studied all that thoroughly. That means more research on your end and sifting through information. For that reason, I’d only recommend them to experienced keepers of freshwater crabs. You need to be able to think on your feet to keep them in the long term.
9. Thai Devil Crab
Scientific Name: Cardisoma carnifex
Size: 5”
Care Level: Easy
Special Care: Primarily Terrestrial
The Thai Devil Crab is one of the largest freshwater crabs known and they’re easy enough to take care of. You just need to be able to set up a tank that’s designed primarily for land crabs and you’ll be fine. In the wild they spend their time on land in mangroves, searching through the soil endlessly for detritus to devour.
The amount of land is a big concern for these crabs. You should have at least 80% of the tank’s available surface as dry, which would barely qualify it as a paludarium. On the one hand, it’s kind of a pain since maintaining such low water levels is tedious. On the other hand, it also makes it easier to avoid them escaping.
And they will escape. All crabs are prolific climbers and escapes happen frequently. In this case, we have a couple of extra problems. The first is their size and the strength that comes with it. These crabs may be able to move light tank hoods out of the way, break things that enter their path, and generally require more physical security. They’ll also do a number on your feet if you get too close when they’re in the middle of an escape attempt.
Reinforcing a tank is trivial, but until you know where the crab is going to break through it can be hard to know where to act. Just keep an eye on your crab in their new home and watch for places that they frequently climb. Once that’s taken care of, these crabs are remarkably easy to keep.
Tips for Keeping Freshwater Crabs
Crab keeping requires a bit more knowledge than most of our aquatic arthropods. It’s not hard, it just requires some different thinking than you’re used to if you only keep fully aquatic animals.
The following tips should help you keep them successfully:
- Study your crab’s diet before bringing them home. Many will scavenge the bottom and be low maintenance, but others are carnivores and require meaty foods.
- Crab-proofing tanks is a pain but it’s easy enough to handle. Clear packing tape is your best friend for the majority of species. You should also work to make cords and air lines inaccessible since the crab will climb out of them.
- Pinches are going to happen if you’re working with crabs. None of the above are capable of serious damage but Red Claw Crabs, Thai Devil Crabs, and Rainbow Land Crabs can all draw blood on the unprepared.
- Turtle docks are great for crabs that only need a little bit of land, such as Fiddlers and Vampire Crabs. These float at the surface of the water, and you can place a stick or lightweight stone nearby to allow them to climb to the top.
- Predatory crabs are much faster and more agile than you think. They’ll catch any fish they can. Unlike fish, crabs tear things up to eat them, which means any fish that’s caught is going to end up being devoured no matter the size of the crab.
- Low pH is a killer, it will eat at the shells of the crabs. Test regularly.
- For once, hard water is a good thing since calcium is required for the shells of crabs. If you use RO water or have naturally soft water then you may want to add a calcium supplement.
- Escape is the number one killer of captive freshwater crabs. Always be vigilant for escapees since acting fast is life or death for the crabs in your care.
- Crabs regrow limbs, so don’t freak out if they lose a leg or eyestalk. They’ll regrow them when they molt. Remove crabs that have lost their claws to quarantine until they molt. Eyes can take 2-4 molts to grow in, but they too will regenerate.
With the above in mind, you’ll be in good hands.
What to Do About Escaped Crabs
Escaped crabs will die in anywhere from a few hours to a few weeks depending on the species and your home. They’ll simply dehydrate if they don’t have it.
Of course, most freshwater crabs are also tiny and can fit into nooks and crannies all over the home.
That said, there are a couple of ways to improve your odds of finding them.
I’ve had luck setting out a jar of water with sheer sides and a ramp leading to the surface from the ground. The crab will try to get water, fall in because crabs are remarkably clumsy, and be unable to get out.
It’s also a good idea to set out a shallower dish of water the crab can climb over. I usually place these in the center of the room instead of along the sides, since it doesn’t actually trap the crab. The idea is to catch it as it retreats when you walk into the room or at least keep it alive long enough to find it.
While these methods aren’t fool-proof, they can help you find your crab and get them back to safety. I’ve personally kept about fifty freshwater crabs of various species over the years. All escaped at least once but only three were found dead.
The biggest thing is to provide some sort of water access however you can. This will often keep your crab alive long enough for them to be found.
Just make sure to correct the problem in the tank as well, or the crab will pop right back out as soon as possible.
Don’t Get Crabby About Your Crabs
In the end, the freshwater crab that’s best suited for your tank is going to be different depending on your circumstances. Finding the right fit can be the difference between life and death for both the crab and other creatures in the tank, so make sure that you give the matter some thought.
No reason to get crabby! The above information will help guide you to the crab you always wanted.
