While some сrab species have gained popularity among aquarium enthusiasts, numerous other species are often overlooked as potential pets – Potamon potamios is one of them.
Potamon potamios, commonly known as the European freshwater crab, exhibit a semi-aquatic lifestyle, making it an intriguing addition to paludariums.
Unfortunately, there isn’t a ton of info out there about these guys, and that’s where I come in. In this article, I will examine the biology, habitat, behavior, and care needs of Potamon potamios.
| Despite the wide distribution of this species, Potamon potamios is included in the IUCN Red List as near threatened because of pollution from pesticides. |
Quick Notes about Potamon Potamios
| Name | European freshwater crab |
| Other Names |
Levantine freshwater crab |
| Scientific Name | Potamon potamios |
| Tank size (minimum) | 10 gallons (~40 liters) |
| Type | Semi-terrestrial |
| Keeping | Easy |
| Breeding | Medium |
| Average size (carapace) | up to 2 – 3 inches (5 – 7 cm) |
| Average size across the leg span |
4 – 6 inches (10 – 15 cm) |
| Optimal Temperature | 71 – 79°F (22 – 26°C) |
| Optimal Humidity | 50 – 70% |
| Optimal PH | 7.0 – 8.0 |
| Diet | Omnivore |
| Temperament | Aggressive |
| Life span | 6+ years |
| Color Form | White-dark and purple-to-black color pattern |
Etymology of Potamon Potamios
The genus name “Potamon” can be traced back to the ancient Greek word “Ποταμόν”, which means “Flood” or “Rapid flow”. The species name “Potamios” is derived from the Greek word “Ποταμίος”, which means “Little or small stream”. Overall, the etymology of “Potamon Potamios” reflects the concept of small fast-flowing rivers and streams.
Taxonomy of Potamon Potamios
These crabs belong to one superfamily Potamidae, which includes all freshwater crabs.
- Kingdom: Animalia
- Phylum: Arthropoda
- Subphylum: Crustacea
- Class: Malacostraca
- Order: Decapoda
- Family: Potamidae
- Genus: Potamon
- Species: Potamios
At the same time, because of their wide distribution in remote areas, there has been limited mixing of the genetic pool of this species, which has allowed for the emergence of numerous subspecies.
Currently, there are 7 subspecies that are considered valid:
- Potamon potamios ssp. Cyprion Pretzmann, 1962,
- Potamon potamios ssp. KaramaniPretzmann, 1962,
- Potamon potamios ssp. KarpathosGhiavarini, 1934,
- Potamon potamios ssp. cretaionGhiavarini, 1934,
- Potamon potamios ssp. PalestinianBott, 1967,
- Potamon potamios ssp. potamios(Olivier, 1804),
- Potamon potamios ssp. schoenmanniPretzmann, 1986 (Naxos Island).
Distribution of Potamon Potamios
Potamon potamios are primarily distributed in freshwater habitats in Eastern Europe and the Near East. This species can be found in various countries, including the Balkans, Greece (mainland and south-eastern Aegean Islands), Russia (South regions), Cyprus, southern parts of Turkey, Palestine, Syria, Lebanon, northern Iran, Israel (Dead Sea area) and Egypt (Sinai Peninsula)
Habitat of Potamon Potamios
Potamon potamios are usually found under stones in the shallow water of temperate rivers and streams where these crabs are adapted to be semiterrestrial and can dig deep burrows into muddy substrates.
Description of Potamon Potamios
This is a medium-sized crab that usually grows up to 2 – 3 inches (5 – 7 cm), but in exceptional cases, it can reach up to 4 inches (10 cm).
According to the study, distinguishing characteristics include:
Carapace. The carapace is slightly arched, smooth, and concave. Anterior lateral carapace margin is well-developed and has numerous very small, rounded teeth.
Gonopod. The first gonopod is conical or slender, without a swollen mesial part.The terminal joint of the first gonopod is elongatedly conical, with the mesial part not curved outwards. The flexible area between the two segments is noticeably double-lobed.
Chelipeds. The claws are relatively large and unequal in length. They have high-ridged teeth that create a gap when closed and are alternately set with one larger and three to four smaller knots.
Interesting fact: The taxonomy of Potamon is based predominantly on characters of the male reproductive organs (the gonopods).
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Lifespan of Potamon Potamios
Currently, there are no studies regarding the maximum lifespan of these crabs in the wild. In nature, they often face risks such as predation, disease, and adverse environmental conditions. These factors can reduce their lifespan.
However, in controlled and under optimal conditions, Potamon potamios can live at least 5 – 6 years in our paludariums.
Typical Behavior of Potamon Potamios
Potamon potamios is not social. On the contrary, they are known for their aggressive and territorial behavior, especially during the breeding season.
These crabs are active, both in water and on land. They are very agile and can be observed moving between aquatic and terrestrial environments in search of food and shelter.
Their semi-aquatic (amphibious) lifestyle allows them to explore a variety of habitats. It was noticed that males can easily spread over the surrounding terrestrial habitats, straying up to 130 ft (40 m) away from the stream at night.
While Potamon potamios are primarily nocturnal, they also exhibit some diurnal behaviors, especially large individuals.
This species can be classified as secondary burrowers. Although they can dig burrows in muddy substrates, they do not rely on them and do not spend all of their time there.
Features:
- Social: No
- Active: Yes
- Peaceful: No
- Territorial: Yes
- Burrowers: Yes
Diet of Potamon Potamios
Potamon potamios is an omnivore and opportunistic species.
According to the study, in its feeding habit, this species behaves as a generalist, actively preying on frogs, fish, and various small invertebrates, as well as scraping alga-covered surfaces or grazing on vegetable debris, mainly consisting of dead leaves and plants. Cannibalism is also present between unequal in size individuals.
If these crabs are kept as pets in paludariums, suggested foods include:
- leaves,
- plants,
- vegetables,
- crushed snails,
- earthworms,
- dead fish or shrimp,
- frozen blood worms,
- Detritus worms,
- Tubifex worms,
- Blackworms, etc.
Features:
- Diet Type: Omnivorous
- Food Preference: Mix of meats and vegetation.
- Feeding Frequency: 3 – 4 times a week for adults. Daily for juveniles.
Rules of Diet in Captivity for Potamon Potamios
- Leave their food for 24 hours before removing it. To prevent water contamination, leftover feed should be removed by siphoning before fresh food is added. Leaves can be left for several days in the tank.
- Leave old exoskeletons. Do not remove molted exoskeletons. They will eat it later.
- Check their hiding places. Keep in mind that Potamon potamios may drag and store food in their hiding spots for later consumption. Check them from time to time to prevent any bacterial contaminations.
- Diversity. Crabs need diversity in food. Do not give them the same food all the time. Change their diet periodically.
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Are Potamon Potamios Plant Safe?
No, they are not. It is not recommended to keep them in beautifully planted tanks. There is a very high chance that they will eat, cut, and shred any plant they can get.
The only viable options for this species are:
- plastic plants,
- floating plants,
- some cheap plants that you are ready to lose.
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Calcium and Crabs
Crabs, like other crustaceans, depend on calcium, particularly during their molting period. This mineral is necessary for the development and maintenance of their hard exoskeleton, which provides protection and support.
Insufficient intake of calcium can lead to weakened shells and deformed limbs. Therefore, it is crucial for crabs to have access to a balanced diet that includes sources of calcium, such as algae, or supplements specifically formulated for crabs.
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Tank Requirements and Water Conditions
Potamon potamios are not fully aquatic animals. Although they spend most of their lives in water but still have some degree of terrestrial activity. Therefore, it is crucial to address their core needs.
Here are some care guidelines to help you out.
Tank Size (Enclosure):
Potamon potamios do not require a lot of space. So, a 10-gallon (40 liters) tank can house 1 adult crab. One male and 1 female can be kept together in the same enclosure of 15 gallons (60 liters).
Males should not be kept in the same tank because of aggression and territorial fighting.
| Stocking is one of the most important factors when it comes to keeping most crab species as pets. Overcrowding is a major source of stress for crabs. In most cases, it leads to health problems, aggression, and cannibalism. |
Note: Potamon potamios are excellent escape artists. They can easily climb vertical surfaces, and often they use this ability to escape from any tank. So, a tight-fitting lid is essential.
Land vs Water Ratio:
It is very important to remember that Potamon potamios is a semi-terrestrial species. Although these crabs are more aquatic, they do not stay in water all the time.
The water area should take at least 70-80% of the space in your tank.
- These crabs molt (shed their old exoskeleton) in water.
- In nature, water also provides more hiding places and, generally, is a safer place.
Water Requirements:
- They need only freshwater.
Note: Results of the experiments showed that Potamon potamios could survive in seawater for at least 2 weeks. Nonetheless, they never voluntarily enter saltwater. - The water only needs to be a few inches deep. It should be big enough to completely submerge your crab and nothing more. As long as water pools can completely cover their entire bodies, they will be fine.
- It also should have some hiding places. Remember, these crabs molt in the water.
- It is crucial to provide a variety of surfaces for them to get out of the water. You also can place some rocks or driftwood in the water to create small islands that the crab can climb onto.
Classic Paludarium Setup
If you do not want to use water bowls and decide to go for a classic paludarium setup for Potamon potamios, you need to know their preferences. These crabs thrive in water with:
pH: a pH range of at least 7.0 – 8.0.
Hardness: KH 0 – 10 and GH 4 – 16.
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Temperature:
The optimal temperature should be in the range of 71 – 79°F (22 – 26°C).
According to the study, this species is physiologically equipped to cope with hot spells even if water is scarce, surviving, at least in the laboratory, up to 21% water loss and remaining alive even at 98°F (37°C) in dry air for 24 h
Humidity:
Their relative humidity should be between 50 – 70%. Humid air lets them breathe properly.
In their natural habitat, relative humidity ranges from 38% during daytime hours in summer to 75% during the night in winter. July is the driest month (daily average 54%), whereas January is the dampest (daily average 72%).
Lighting:
No special requirements. You may not even need one.
However, if you have plants, lighting should be adapted to their needs.
Substrate:
You can have any substrate in their habitat. However, in my opinion, it is better to use some that will allow them to burrow if they decide to.
Decorations:
Decorations play a role that goes beyond pleasing us visually.
In reality, their only function is to provide shelter for the crabs. So, the more decorations you have, the happier your pets will be.
They will appreciate all types of leaves, rocks, driftwood, PVC pipes, etc. in your tank.
| Important: If there are no suitable hiding places available (even if there are no predators in the tank), the crab will feel stressed all the time. As a result, it will shorten its lifespan and can make it aggressive. |
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Rules: How to Care and Handle Potamon Potamios:
- These crabs are not pets you can play with. Do not take them out just because you want to.
- They should never be lifted up by their legs or claws!
- Do not leave uneaten food for too long. It can cause smell and bacteria in their enclosure. Remember, these crabs like to store uneaten food in their burrows.
- Provide as many hiding places as you can.
- Keep the warm temperature and high humidity.
- Make sure the lid of the tank is closed tightly so that they cannot escape it.
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Molt Cycle of Crabs
Periodic molting is vital for the growth of all crustaceans. This process is characterized by a complete replacement of the old mineralized exoskeleton with a new one.
This process consists of 4 phases:
- pre-molt,
- molt,
- post-molt.
- inter-molt.
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Important:
- NEVER disturb your crabs when they are molting.
- Do not panic even if you have not seen them for a few days in a row! The molting cycle may extend over days. So, give them time. This is the most stressful moment in their life.
- Keep putting and replacing food in the tank! You never know when they can come up from the molt.
- Keep giving them calcium-rich food.
- Also, do not remove the old exoskeleton from the tank. The crab exoskeleton is multi-layered and consists of calcified chitin, protein, and lots of minerals. Your crab will eat it later.
Breeding Potamon Potamios
This species has a direct development without free-swimming larvae in the sea.
Maturity:
Mature males start to show significant changes in claw length at around 1.4 inches (3.5 cm) carapace length. In females, the transition to maturity seems to occur between 1 – 1.4 inches (28 – 35 mm) carapace length.
Sexing:
- Claws. Male chelipeds exhibit positive allometry concerning carapace length, presumably due to their role in intra and/or intersexual competition.
- Abdomen. Females have a wider abdomen (than males), and their allometric growth decreases after the puberty molt.
- Size: On average, males are larger than females. This size advantage increases their likelihood of successful copulation. Conversely, the optimal size for females appears to be influenced by the energetic expenditure required for reproduction.
Mating:
When a female is ready to mate, she signals her receptiveness by allowing a male to approach. During mating, the male assumes a dominant position by flipping the female upside down and wrapping his body around her to fertilize.
Fecundity:
According to the study, Potamon potamios generally has from 75 to 215 eggs. Similar to other Potarnoidea species, eggs are incubated in the chamber limited by the sternum and abdomen, and the hatchlings remain under the female abdomen for a certain period before dispersing.
Incubation and Hatching:
Incubation generally lasts around 1 month. The eggs hatch into miniature versions of the adult.
Potamon Potamios and Suitable Tankmates
Since these crabs are quite aggressive and territorial, the ideal situation for Potamon potamios is a species tank.
Interesting fact: During the experiment, pairs of equal-sized individuals (Potamon potamios and Procambarus clarkii) were evaluated for aggressiveness, domination in fights, and shelter occupation. Results showed that even though both species are similarly aggressive, the crayfish wins more fights and occupies shelter more efficiently than the crab.
Bad Tank Mates:
- Fish.
Any crayfish species. - Other crab species.
- frogs.
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In Conclusion
Potamon potamios can be a good choice for even novice aquarium enthusiasts, provided you understand its specific requirements. As a semi-aquatic species, these crabs thrive in a paludarium environment.
Nonetheless, while Potamon potamios may be relatively straightforward to care for in terms of habitat, their compatibility with other aquatic inhabitants can be a problem since they are territorial and aggressive.
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References:
- Gherardi, Francesca, and Fiorenza Micheli. “Relative growth and population structure of the freshwater crab, Potamon potamios palestinensis, in the Dead Sea area (Israel).” Israel Journal of Ecology and Evolution36, no. 3-4 (1989): 133-145.
- Bolat, Yildiz, Şengül Bilgin, Ali Günlü, Levent Izci, Seval Bahadır Koca, Soner Çetinkaya, and Habil Uğur Koca. “Chitin-chitosan yield of freshwater crab (Potamon potamios, Olivier 1804) shell.” Pakistan Veterinary Journal30, no. 4 (2010): 227-31.
- Bilgin, Şengül, and Zeliha Ufuk Canlı Fidanbaş. “Nutritional properties of crab (Potamon potamios Olivier, 1804) in the lake of Eğirdir (Turkey).” Pak Vet J31, no. 3 (2011): 239-243.
- Ali, Malik H., and Tariq HY Al-Maliky. “Fecundity of the crab, Potamon mesopotamicum Brandis, Storch & Turkay, 1998 from the Mesopotamian Marshlands, Iraq.” Journal of Fisheries and Environment41, no. 3 (2017): 6-11.
- R Warburg, S Goldenberg, Water loss and haemolymph osmolarity of Potamon potamios, an aquatic land crab, under stress of dehydration and salinity, Comparative Biochemistry and Physiology Part A: Physiology, Volume 79, Issue 3, 1984, Pages 451-455.
- Savvides, P., Louca, V. & Sfenthourakis, S. Competition for shelter occupancy between a native freshwater crab and an invasive crayfish. Aquat Ecol 49, 273–278 (2015).
- IUCN (2014) Red list of threatened species. http://www. iucnredlist.org. 27 Sept 2014