Crabs are becoming more and more common in the hobby as new species are found. Like most “freshwater” crab species, the Red Claw Crab is a partially aquatic brackish water species. This means that they need both land and salt to survive. Without these things they won’t last very long so you’ll need to design their tank accordingly.
Fortunately, Red Claw Crab care is about as easy as it gets! While they do need some salt and a patch of dry land, these are undemanding and a great entry into the crustacean world. Who knows? Maybe you’ll decide to keep other crabs alongside them!
- Scientific Name: Perisesarma bidens
- Origin: IndoPacific region
- Size: 3 inches
- Aquarium Size: 10-20 Gallons
- Difficulty: Easy
Red Claw Crab Care
In this section we cover everything you need to know about Red Claw Crab care:
Aquarium Size
Red Claw Crabs rarely grow beyond 3 inches in diameter. They grow fast but also die young: 2 years is quite old for one. Therefore, they don’t require much space at all.
While a 10 gallon aquarium can house a few Red Claw Crabs, a 20 gallon long is better. The longer footprint (30″ x 12″ x 12″) gives you plenty of space for both the water and land portion without feeling too crowded. Not being crowded is especially important for molting crabs, which we’ll discuss in a bit.
If you prefer designing an even larger paludarium then larger aquariums work as well! They also provide space for decorations like mangrove roots and driftwood for your crabs to crawl up and across.
You should provide at least 30 gallons of space if you want to keep them with other partially aquatic crabs, like Fiddler or Thai Devil Crabs.
Water Quality
Red Claw Crabs are found in tropical regions around the Indian and Pacific Oceans. The mangrove swamps that form around river deltas and tidal marshes are where you’re most likely to find them.
Therefore, you should maintain the water temperature around 72-78℉, with a chemistry between neutral to alkaline (pH 7.0-8.5).
Land access is important to Red Claw Crabs but so is salinity. These crabs are not purely freshwater animals. They live in brackish regions around the world where rivers meet the sea.
Salt levels fluctuate here so they are often exposed to nearly pure fresh and saltwater throughout the month. However they need some salt to thrive in captivity. A specific gravity of 1.005, slightly brackish, is perfect for them long-term.
You should use a hydrometer for marine hobbyists to ensure the salt levels are where you want them to be. Red Claw Crabs can tolerate both full marine and freshwater conditions so some fluctuation is great, just not all at once.
Plants and Substrate
While Red Claw Crabs don’t disturb live plants they are mostly impossible to grow in a brackish paludarium. Your best bet is to keep small pots of terrestrial plants with the pots buried in the substrate.
Mangroves would normally thrive here however they are trees and eventually grow much too large. Fortunately, a few freshwater favorites are very tolerant of mildly brackish water!
Cryptocoryne can be found in tidal marshes in their homeland of Sri Lanka. C. wendtii is one of the largest and easiest to grow. It even grows emersed, allowing you to create a forest leading out of the water!
Anubias is another plant that tolerates brackish water. These epiphytes grow very slowly but need next to no special care. Attached to driftwood or a rock, they will eventually secure themselves and may even flower once established.
Red Claw Crabs prefer sand, mud, and silt substrates, which is what they would be living on in their natural river delta habitat. They collect particles of food much easier and the crabs will often take mouthfuls of sand in, sucking out bits of food and leaving mud balls behind.
If you have multiple crabs and other animals in your paludarium you’ll need to provide hiding places for molting crabs. All crabs need to molt every few months.
Their hard shells provide armor but don’t grow with them. Once a crab sheds its shell, it’s vulnerable for a few hours. However their worst enemies are often other crabs!
Once a fellow crab senses his neighbor is weak he’s likely to grab onto him and start eating. So make sure you have rocks, driftwood nooks, plants, and other places for molters to lay low until their armor hardens.
Tank Mates for Red Claw Crabs
Crabs are some of the hardest aquarium inhabitants to find tank mates for. Crabs are opportunistic predators: if it’s smaller than them, they will try to eat it. But if it’s larger than them, there’s a good chance the crab will end up as lunch!
Many fish enjoy crabs, especially a soft, freshly molted one. So you’ll need to avoid some of the most popular traditional brackish water fish: puffer fish. All puffers are invertebrate eaters.
Medium-sized brackish water fish like Mollies and larger Gobies are best. Young Scats (Scatophagus sp.) are unusual but relatively easy to find. They can grow large though, and need at least 55 gallons of space as adults. So stick to young fish as tank mates.
Great Tank Mates for Red Claw Crabs:
- Mollies
- Fiddler and Thai Devil Crabs
- Flagfish
- Larger Gobies
- Young Scats
Poor Tank Mates for Red Claw Crabs:
- Salt-intolerant fish and plants
- Small fish like tetras and guppies
- Shrimp and snails (too defenseless)
Feeding Red Claw Crabs
Feeding is the easiest part about Red Claw Crab care! Like all Crabs they are opportunistic omnivores: if they can catch it, they will eat it! Bits of fresh or rotting meat like clam, fish, or chicken are their favorite.
However they will happily eat prepared crab formulas, flakes, pellets, worms, frozen fish food, and anything else you offer them. In nature, a dead, rotting fish washed up onto the river bank is a feast for them. So rest assured knowing that Red Claw Crabs are not picky eaters!
Crabs are very messy eaters, however. So keep a close eye on their water conditions as ammonia, nitrite, and nitrate levels can rapidly become toxic. Like all invertebrates they are sensitive to all three compounds.
Remember that a paludarium has less water than a standard filled aquarium. Red Claw Crabs can quickly become poisoned if there isn’t a filter running and you skip a few water changes.
Sexing and Breeding Red Claw Crabs
In order to sex your crabs, take a look at their claws and undersides. Males have significantly larger claws and a pointed abdomen curled against their body. Females have a much more rounded abdomen and smaller claws.
Males also tend to be quite territorial and prefer living in small harems alongside a group of females. While it’s possible you may keep your crabs happy enough for them to lay eggs, breeding them is nearly impossible in captivity.
Like nearly all crabs their larvae go through a planktonic stage. Free-floating and microscopic, these larvae drift along in the ocean, eating phyto and zooplankton until they grow large enough to sink to the bottom. Within just a few months they return to the sandy tidal marshes where they were born as miniature crabs.
Since aquariums can’t provide the plankton they need – and young crabs are likely to get sucked into an active filter – breeding them is extremely difficult unless you create a specialized habitat to do so.
Image credit – RockStarRei at English Wikipedia, CC BY-SA 3.0, via Wikimedia Commons
