Potamonautes lirrangensis – Blue Malawi Crab
Potamonautes lirrangensis was described in 1904 by Mary J. Rathbun , then as Potamon lirrangensis. In 1907 Cunnington described Potamon orbitospinus. In retrospect, these were one and the same species.
In many shops you often see the old name: Potamonautus orbitospinus. This is a synonym that should no longer be used. Because Potamonautes lirrangensis was described earlier, this is the official name and Potamonautus orbitospinus has become a synonym.
Their common name is Blue Malawi Crab.
Description
The shell of Potamonautes lirrangensis can reach a width of about 10 centimeters. Including the legs, the overall width is approximately 15 centimeters, and it can expand to 20 centimeters when the legs are fully spread. While the common name suggests that the Blue Malawi Crab is blue, its color can actually vary from brown to blue. Additionally, red coloration can be observed on the joints.
The difference between males and females is clearly visible in the abdomen. In the female, this is much wider than that of the male. This is the tail of the crab. This is folded up under the body. The female stores the eggs between the tail and the abdomen. Here, they are safe from predators.
Character
Potamonautes lirrangensis is best kept solitary. They generally do not tolerate other members of their species nearby. Even a 150 cm long aquarium with sufficient hiding places is often not big enough.
Only during mating do Blue Malawi Crabs come together. But even then, it can happen that the female is killed by the male.
Biotope
The Blue Malawi Crab is not only found in Lake Malawi. You can also find them in Lake Kivu, the Congo and the Malagarasi rivers. They are not endangered in the wild, partly due to the large distribution area where they occur.
Diet
Like many crabs, the Blue Malawi Crab is omnivorous. They will eat just about anything edible. You can feed them vegetables, fruit, sinking granules, wafers, pieces of fish, shrimp, mussels, snails, etc.
They do not usually eat live fish. Only sick and weak animals that cannot swim away are eaten. They are scavengers and not hunters.
The Aquarium
As mentioned, Potamonautes lirrangensis is best kept solitary. If you only keep the crab, you can keep them in an aquarium of about 100 liters. However, they are usually kept in a Malawi aquarium. The minimum size should then be about 150 centimeters in length.
Set up the aquarium with sand on the bottom. Place rocks in such a way that there are holes, cracks and crevices where the crab can hide. Make sure the rocks are firmly in place so that they do not move when the crab crawls between them.
You can keep the Blue Malawi Crab with not too large fish species. When a crab molts, its new shell is still soft. Too large predators can then attack the crab and eat it. That is a shame for your beautiful crab.
Land area
In some descriptions, it is mentioned that this crab requires a land area. However, that is not accurate. In Lake Malawi, for instance, they live at a depth of about 50 meters and do not come above water. This does not mean that you cannot create a land area for Potamonautes lirrangensis; they can still occasionally climb onto dry land.
Escape
Please note that the Blue Malawi Crab is a real escape artist. They can climb very well. An open aquarium is not suitable for this species. Make sure that the aquarium or paludarium has a well-fitting lid!
Breeding Blue Malawi Crab
Breeding in the aquarium is difficult. As mentioned, Potamonautes lirrangensis does not tolerate other crabs in their environment. They do not hesitate to eat their own kind. This can even happen in an aquarium of 8,000 liters.
After mating, the female takes care of and guards the eggs and young crabs under her body. As soon as the young crabs leave the mother, they already look like the adults, of course, much smaller. A single litter can produce up to a few hundred young crabs.
Video
Author
John de Lange
Copyright images
Pete Barnes
Martin Grimm – CC BY-NC 4.0
References
Rathbun, M.J. (1904). Les crabes d’eau douce (Potamonidae). Nouvelles Archives du Muséum d’Historie naturelle. Nouvelles Archives du Muséum d’Historie naturelle, series 4. 6: 225-312.
Iucnredlist.org
Commons.nmu.edu
Aquaticcommons.org
Garnalenforum.be
Wikipedia
Aquagids.nl
database.gek.nu
