When it comes to invertebrates, many aquarists immediately think of shrimp or crayfish. However, there’s another group of fascinating inverts that can be kept in aquariums: crabs! Unfortunately there is still a lot of misinformation out there about these clawed critters. Many brackish crab species are sold as suitable for freshwater tanks and many species that require a land area are marketed as “fully aquatic”, which inevitably leads to dead crabs and disappointed aquarists.
All this conflicting info can be rather confusing: which crab should you go for? Do they need brackish or fresh water? To hopefully clear things up a bit, this list contains five fully freshwater crab species!
Thai micro crab (Limnopilos naiyanetri)
With a carapace size of around 1 cm (0.4 inch), Thai micro crabs are by far the smallest crab species on this list. These tiny crabs are fully aquatic and naturally found in a freshwater river in Thailand. Introduced into the aquarium hobby not too long ago, they are still not very well-known but quickly gaining popularity and becoming more readily available in aquarium stores.
Thai micro crabs can be quite shy and are relatively fragile, which makes them most suitable for very peaceful tanks with plenty of hiding places. They make a good addition to heavily planted dwarf shrimp aquariums and other calm setups without active or carnivorous tankmates. Never introduce them into improperly cycled aquariums, as they don’t respond well to fluctuating water values
Vampire crab (Geosesarma sp.)
The various colorful crabs from the Geosesarma genus (such as Geosesarma dennerle; pictured at the top of this article) are often collectively referred to as vampire crabs due to their yellow eyes that almost seem to glow. Although they are actually not fully aquatic and therefore not suitable for normal aquariums they are included on this list because they do still need access to an area with fresh water. If you’re interested in keeping them be prepared to venture into the world of paludariums, which mostly consist of land area but contain some water as well.
For a small group of vampire crabs a heated paludarium of at least 15 gallons (57L) is recommended. A ratio of 2/3 land and 1/3 water should be a good place to start; your land area can be heavily planted with various types of moss and other plants. The submerged area should be cycled and water should be relatively hard with a higher pH. Like most other crab species, vampire crabs are omnivores that can be fed a varied diet consisting of invertebrate pellets, insects, vegetables and pretty much anything else!
Tanganyika crab (Platythelphusa sp.)
Although not very popular in the aquarium hobby yet, crabs from the genus Platythelphusa, which are naturally found in Lake Tanganyika, are definitely an option to consider for aquarists looking to set up a (Tanganyika biotope) aquarium for a fully aquatic crab species. Specific care requirements for these crabs are still relatively difficult to find, not in the least because the different subspecies are not always identified correctly even though their size varies quite a bit; at around 6 cm (2.4 inches) Platythelphusa armata is the largest.
A small aquarium is probably not a good choice for Tanganyika crabs, as like all crabs they need to be able to find a hiding place when it’s time to molt. A tank of at least 20-30 gallons (76-114L) is probably a good starting point. Be sure to keep in mind that these crabs are not community safe and will consume everything they can get their claws on. They are said to have an appetite for aquarium snails and will not hesitate to catch weak fish if they get the chance, although they can probably be kept safely with many quick Tanganyika cichlid species. As with all crabs, be sure to use an aquarium hood and cover all holes to prevent escape.
Panther crab (Parathelphusa pantherina)
Although not the easiest freshwater crab species to keep in the aquarium, panther crabs originating from Sulawesi can make an interesting project for more experienced aquarists. With a carapace size of up to 8 cm (3.1 inches) they are one of the larger crab species on this list, which means they require a relatively large aquarium (at least 20 gallons/76L for one crab). Tank size is especially important when housing multiple crabs together, as they are quite aggressive both towards their own species and other tankmates. Keeping pairs or harems is usually the way to go: multiple males don’t seem to go too well together.
Although panther crabs are usually considered fully aquatic, some sources do suggest a small amount of land area in the form of wood or rock that reaches beyond the surface. Like all crab species, panther crabs require plenty of hiding places such as coconut hides as they are very vulnerable during molting time.
Freshwater pom pom crab (Ptychognathus barbatus)
Like their saltwater namesakes, freshwater pom pom crabs lend their name from the pom pom-like filters on their claws. Still quite uncommon in the aquarium hobby and probably not very easy to find, freshwater pom pom crabs are definitely worth the search for anyone looking for an unusual addition to a (nano) aquarium. They are fully aquatic and a little larger than Thai micro crabs but, unlike most of the other species on this list, still quite peaceful and community-proof. Most sources report them paying no attention at all to even the smallest tankmates, including dwarf shrimp such as cherry shrimp.
I look forward to seeing more of this small but active crab species in the future!
Many of the crabs sold in aquarium stores as suitable for fresh water should actually be kept in brackish setups. Species that are commonly wrongly sold as freshwater include red claw crabs (Perisesarma bidens), fiddler crabs (Uca genus) and hermit crabs. Always do some research before purchasing a crab and be sure to look at multiple sources!
If you have any more questions about freshwater crabs, have a species to add to the list or want to share your own experiences with any of these species, don’t hesitate to leave a comment below! New freshwater crab species are discovered and subsequently introduced into the aquarium hobby regularly so new developments are not uncommon.
Cover photo: Geosesarma dennerle 1.jpg by Nicholas Palm.