Wrongcrowd.com - Freshwater Red Clawed Crabs

Water Conditions

Shortly after I started this page, a reader found water conditions in in a book and sent them to me. I have since updated the table above with new information from other keepers which I believe to be more accurate. In particular, the temperature range was expanded and the preferred pH changed from neutral to slightly high (for freshwater anyway). Note that Jeremy Gay and others claim them to be intolerant of high ammonia, nitrite and nitrate. It's certainly a good idea to keep your water clean no matter what you keep though!

Salinity

Opinions on water salinity for this species vary. Frank Greco writes that while they range from fresh to brackish water in nature, in captivity it is best to keep them in 5-15 ppt salinity. That is 1/6 to 1/2 the salinity of seawater. My own experience agrees that keeping them in 100% fresh water is not tenable in the long term.

Trace Elements

The trace elements in sea salt are beneficial to these creatures. Consequently, natural or synthetic sea salt should be used in their habitat as opposed to plain salt. Interestingly, Frank G. also writes that in his experience iodine supplements help reduce mortality during molts. Try a reef aquarium iodine/iodide supplement if you are having problems with molting, but be careful not to overdose.

Copper is dangerous to all inverts, but the levels present in some aquarium plant fertilizers should not be harmful. It would be wise to avoid copper-based medications for any tank with inverts, though.

What Kind of Salt?

The best choice for your crabs' health is salt designed for salt water aquariums. Sea salt has a lot of trace elements that plain salt lacks.

In an emergency, you can probably get away with plain salt, but switch back to the good stuff as soon as you can. If you need to get salt at the grocery store, make sure it does not have an anti-caking agent such as prussic acid. Diamond Crystal kosher salt is good, and so is Morton's canning and pickling salt. Other types may work too--just make sure they are 100% pure salt with no additives. And don't use plain salt longer than you have to!

Feeding

These crabs eat pretty much anything that settles to the bottom of the tank. I feed Hikari loach wafers, Wardley shrimp pellets, and dried tubifex worms. In my own experience they do not care for veggies, but many readers have told me that their crabs have torn up some plants. All I know for sure is that my Java fern was left alone, but your mileage may vary. You may also wish to try algae wafers, zucchini, boiled spinach and peas for your RCCs.

Air

Some crabs, like fiddlers, need access to the air to survive. RCCs are like this. You may get lucky and keep them completely submerged for a time, but it isn't healthy in the long term. Give them an easy way to get out of the water, and some terrain to explore. Just make sure that there is no way for the critter to escape the tank or to get close to the hot lights under the hood. (Yes, this is a reversal of my previous posting, based on experience and communication with other keepers.)

Note that these crabs can climb nearly any cable or hose, plus they appear to be able to swim upwards at least 6". Be careful how you arrange your habitat, and use a tight-fitting hood.

Catching Your Crab

This species is fast and strong for its size. Be very careful when netting it; it will try to climb the mesh and escape. In fact, when I bought my first RCC, the first one they scooped up climbed out of the net, jumped onto the floor, and ran under the rack of tanks. They probably never got it back.

When I need to catch a crab, I use a paper or plastic cup. It's pretty easy to corner it and scoop it up, and it can't climb up the slick sides. Hang up the net.

If your red claw crab ever does escape, it can live for a some hours without water. I hope never to test just how long they can make it, but some readers have found escapees alive the next day. Try putting a dish of water down by the aquarium, or under couches and other hiding places.

Molting

Red clawed crabs seem to molt every few months. I have seen it happen as often as every 2 months, or as long as 6 months.The old exoskeleton looks just like the crab, only transparent. The more they molt, the faster they are growing, and presumably the healthier they are. If your crab has lost a limb or claw, he may regrow it at his next molt!

After the molt you may see your crab turn darker or lighter for a few days. Many people advise leaving the empty shell in the aquarium for the crabs to eat. I've never seen my guys doing that but it certainly can't hurt.

Molting is a stressful time for the crab. If you have problems with death during molting, consider trying an iodine supplement as discussed above.

Disposition

Wild RCCs live in large colonies in damp holes. Males are territorial, and they will fight among themselves—often to the death. Due to this, I would only ever keep a maximum of one male crab in a small tank, or maybe two in a large tank.

Fortunately other critters seem pretty safe from RCCs. The RCC may chase away fish that get too close but neither fish nor crab have ever been injured in my experience—though other keepers have told me of small fish being caught and eaten. Other items of interest: Jason K. tells me that their RCCs get along with their two blue lobsters. My Singapore Shrimp have never been bothered by my RCC either.

Gender

Male crabs have larger claws than the females. The photos on this site will show the difference. The shape of the under-shell is also distinctive. Males have a long, pointy element. The same part on females is wider and more rounded. (Thanks to Taryn R. and Misty J. for this tip, and to Taryn for the photo.)

Breeding

Since I started this page, this species has been bred in captivity! See Jukka J.'s site for all the details. All I will say here is that females carry red eggs under their body. It may look like their shell is opening. (This is easy to see in the pic on S. Swartz's site.)

Medication Tolerance

Long ago I had an ich outbreak among the fish in the crab's tank. I learned that sesarma bidens seems to tolerate malachite green based medications like "RidIch" quite well. The crab showed no signs of stress while the tank was being treated. (Side note: Since then I have learned a better way to treat ich, the "heat + salt" method.)

The "Creeping Death"

Many people have written and asked, "my crab was fine yesterday, but today he is hardly moving... what is wrong?" They may go stiff and flip over on their back. Sometimes the crab will drop legs and claws. While I do not know exactly what causes the "creeping death" I know how it usually ends: badly. Make sure your crabs are in a proper habitat: clean brackish water, access to the air, and the temperature not above 85F. A proper habitat is the best way to reduce stress on the animal.