Aquarists are always on the lookout for unique and rare species to add to their collections, and there are few things more exciting than discovering a species that is both rare and suitable for captivity. Such is the case with the Ghost dwarf crab (Potamocypoda pugil). If you by chance buy one you will be surprised to find out how little is known about them.
Ghost dwarf crabs are a type of freshwater crabs that are sociable and omnivorous, which makes them quite low-maintenance in terms of feeding and care in an aquarium setting. Nevertheless, they do have particular needs, such as warm water and designated spots for them to climb out of the water.
In this guide, I gathered everything we currently know about Potamocypoda pugil including tank setups, habits, diets, compatibility, etc.
Quick Notes about Ghost Dwarf Crab
|Name||Ghost dwarf crabs|
|Scientific Name||Potamocypoda pugil|
|Tank size (recommended)||10 gallons (~40 liters)|
|Average size (carapace)||up to 0.4 – 0.6 inches (1 – 1.5 cm)|
|Average size across the leg span
||1 – 1.3 inches (about 2.5 – 3.5 cm)|
|Optimal Temperature||75 – 82°F (24 – 28°C)|
|Optimal PH||7.0 – 7.5|
|Optimal GH||3 – 12|
|Optimal KH||1 – 5|
|Nitrate||Less than 20 ppm|
|Life span||up to 3 years|
Why Are They Called Ghost Dwarf Crabs?
They are called Ghost dwarf crabs because of their diminutive size and translucent look, which makes them appear virtually invisible in the tank. Additionally, they are generally nocturnal animals and tend to hide during the day, which furthers their reputation as ghosts.
Note: This is just another marketing move because catchy names always attract buyers’ attention and this helps in self-promotion.
The word “Potamocypoda” is derived from the Greek words “Potamos,” meaning “River,” and “Kupodeuein,” meaning “to walk on tiptoe.” It refers to the fact that these crabs have long, slender legs that enable them to move gracefully and quickly through the water.
Distribution of Ghost Dwarf Crabs
This species is endemic to Malaysia. The Ghost dwarf crabs can be found in a freshwater stream the Sungai Kayu located in the swamp forests of eastern Johore. It is a tributary of the River Sedili.
Natural Habitat of Ghost Dwarf Crabs
The Ghost dwarf crabs are restricted to shallow and vegetated, places, surrounded by shaded tropical forests.
Description of Ghost Dwarf Crabs
Potamocypoda pugil is a very small species. Fully grown crabs can reach up to 0.4 – 0.6 inches (1 – 1.5 cm) long (carapace size), with a leg span of up to 1 – 1.3 inches (about 2.5 – 3.5 cm).
Distinguishing characteristics of Potamocypoda pugil:
- Carapace. This species has a broad, somewhat convex carapace that is smoother and more punctate on the branchial regions.
- Color. The carapace is an olive-brown color, and the limbs and underside are a yellowish-brown color.
- Eyes. The orbits are short and the eyes are small and slender.
- Legs. The walking legs are moderately slender and hairy.
- Chelipeds. Males have asymmetrical claws.
Note: It is very easy to confuse Potamocypoda parapugil and Potamocypoda pugil because these species share many characteristics. They even share the same common name – Ghost crabs. Nonetheless, in Potamocypoda parapugil the chelipeds are of the same shape in both males and females.
Lifespan of Ghost Dwarf Crabs
The lifespan of these crabs is unknown. Currently, there is no data available on the maximum lifespan of Potamocypoda pugil in the wild.
However, in captivity, they can live for several years (2 – 3 years on average) if appropriately cared for.
Typical Behavior of Ghost Dwarf Crabs
The Ghost dwarf crabs require permanent bodies of water for survival since they live in open water. Nonetheless, despite being a fully aquatic species, it is worth noting that these crabs can occasionally venture onto land.
Note: Although this behavior is rare, it is recommended to provide them with the opportunity to do so in the aquarium by creating protruding areas above the water level, such as driftwood or rocks.
It has been also observed that these crabs do not exhibit aggressive behavior. Even when engaging in disputes with one another, such conflicts tend to resolve without causing any significant harm. Thus, you will not see them running around with claws and legs missing all the time.
The Ghost dwarf crabs are relatively shy and skittish, especially if they are kept in small groups. The bigger their colony, the safer they feel and the more confident they act, venturing out from hiding more often.
These little guys are not very messy and/or destructive. They are not strong enough to constantly move stuff in the tank.
These crabs are nocturnal. The pick of their activity starts at dusk and gradually stops before sunrise.
Note: Nocturnal behavior is mostly dictated by the risk of being predated upon. This is instinctive behavior.
- Social: Yes
- Activity: Low
- Peaceful: Yes
- Burrowers: No
Feeding Ghost Dwarf Crabs
The Ghost dwarf crabs are considered omnivorous scavengers. It means that their diet consists of both dead or decaying plant and animal matter. In their case, this could include algae, small aquatic organisms, and even detritus (organic matter that has decomposed).
In aquariums, suggested foods for your crabs are:
- blanched vegetables,
- crushed snails,
- chopped blackworms, bloodworms, etc.
- brine shrimp,
- dead fish or shrimp.
You need to feed your crabs bottom-dwelling food along with sinking pellets of any brand (examples with links to check the price on Amazon):
- Shrimp pellets
- Shrimp Granules
- Fish food (TetraMin® flakes, etc.)
- Shrimp food (Hikari’s crustacean food like Hikari Shrimp Cuisine, Algae wafers, etc.)
It is crucial to provide them with a diverse range of food to ensure their well-being. Avoid feeding them protein-rich foods continuously, even if they seem to enjoy it. Instead, offer them a combination of live food that stays at the bottom of the tank and sinking pellets from any reputable brand.
How often should We Change the Food?
Leave the food for 24 hours before removing it. Make sure that whatever they do not consume in one day is removed, otherwise, it will foul up the water and cause a lot of problems.
Keep in mind that Ghost dwarf crabs are mostly nocturnal. So it is recommended to feed them at night (at least in the evening) so that you can replicate the conditions and environment under which they eat naturally.
Ghost Dwarf Crabs and Live Plants
These crabs are safe to keep with any type of live plant. This species does not eat healthy plants and can, therefore, be kept in beautifully planted aquariums. Even more, they will benefit from live plants by cleaning microorganisms from them.
Keeping and Housing Ghost Dwarf Crabs
Due to the small size of crabs, they require a relatively small amount of space. Therefore, a group of 4-6 individuals can be kept in a 5-gallon (20 liters) tank.
However, if possible, it is recommended to keep them in a 10-gallon aquarium. This is because larger aquariums are easier to maintain and provide a more stable environment, which is important for ensuring optimal water parameters.
Temperature: This species requires very warm temperature conditions of 75 – 82°F (24 – 28°C). Ghost dwarf crabs do not tolerate large and sudden temperature fluctuations.
pH: pH should be provided for this species in the range of 7.0 – 7.5.
Hardness: They will appreciate optimal KH 1 – 5 and GH between 3 – 12.
Water flow and Aeration:
These crabs enjoy the water with current and rich oxygenation.
It really does not matter much. You can choose whatever filter you like.
Nonetheless, for small tanks, sponge or Matten filters are the best options. These crabs are too small to damage and tear apart the sponge as large crab species often do. In addition, these filters have lots of advantages:
- easy to maintain, and clean,
- they provide a lot of surfaces to graze on,
- safe for the crabs.
No special requirements. Ghost dwarf crabs are nocturnal animals. Basically, they do not really depend on the light.
However, if you have plants, lighting should be adapted to their needs.
Decorations and Hiding Places:
Make sure that Ghost dwarf crabs have lots of hiding places. They are very skittish.
Decorations provide hiding places (shelter and protection) and minimize their stress. This is especially crucial for the molting process when crabs are weak and extremely vulnerable.
To create a more enriching environment in your tank, you can add a variety of decorations such as leaves, rocks, driftwood, PVC pipes, plastic mesh, plants, etc.
Important: Although these crabs are fully aquatic, it is better to have perches above the water line accessible to them. For example, you can set this up as a piece of driftwood sticking up out of the water.
Ghost Dwarf Crabs – Male and Female Differences
Potamocypoda pugil is sexually dimorphic. There are a few indicators that give away the gender of the crabs.
- Size. Males are generally larger than females.
- Abdomens. Different shapes of the abdomens. Males have a narrow and slimmer plate (triangular) while females have a broad plate on their belly.
- Chelipeds. Females have smaller and slender claws. In addition, their fingers are spoon-shaped. In males, the right or left cheliped is developed as in the female, and the other is greatly enlarged and modified.
- Carapace shape. The longitudinal convexity is stronger in the female, and the anterior part of the carapace of which is inflated.
Breeding Ghost Dwarf Crabs
The reproductive traits of the genus Potamocypoda have not been described in the scientific literature yet. In addition, to date, there have been no reports of successful breeding of these crabs, either in laboratory or home settings. As a result, we are even unaware of the duration of the incubation process or the number of eggs that females produce.
Ghost Dwarf Crabs and Suitable Tankmates
Ghost dwarf crabs are one of the most social and peaceful crab species. Generally, they will not bother anybody. On the contrary, if anything, they are more likely to be on the receiving end of aggression as their small size places a target on their backs from other bigger tankmates.
Ideally, no aggressive, top or middle-dwelling, fast-moving fish can be kept in the same tank with Ghost dwarf crabs.
Ghost dwarf crabs do not hunt shrimp on purpose.
However, I would still be very cautious and would not put them with expensive shrimp. There is always the chance shrimplets can be caught by crabs, especially when shrimp molt.
Generally, Ghost dwarf crabs do not mess with freshwater snails. However, very small snails may be eaten.
Summary of Bad Tank Mates for Ghost Dwarf Crabs:
- Larger or aggressive fish.
- Bottom-dwelling, slow-moving, and fish with long fins.
- Any crayfish species.
- Other freshwater crab species.
- Dwarf frogs.
Given their unique appearance and small size, Ghost dwarf crabs can be a great addition to small aquariums. The main problems though are their rarity in the aquarium trade and the lack of scientific information on how to provide optimal conditions for their care and breeding.
- 佐々木潤. “観賞用に 「ゴーストクラブ」 という商品名で流通していた Potamocypoda parapugil Tai & Manning, 1984 (十脚目: 短尾下目: スナガニ上科: コメツキガニ科).” Cancer25 (2016): 41-45.
- Tweedie, Michael Willmer Forbes. “A new scopimerine crab from the Malay Peninsula.” Bulletin of the Raffles Museum14 (1938): 198-202.
- Dai, Aiyun and Manning, Raymond B. 1984. “A New Species Of Potamocypoda (Crustacea, Brachyura, Ocypodidae) From Malaysia. 1984, Proceedings of the Biological Society of Washington, Volume 97, Pages 615-617