Fast facts on Potamonautus orbitospinus (Malawi crab)
Biotope: Lake Malawi. This crab – the only one living in Lake Malawi as far as I know - occurs everywhere in the Lake. While diving, we found specimens along the Tanzanian shore (i.e.: Higga Reef and Hongi Island to name a few spots), around the Cape MacLear area (i.e.: both Thumbi islands and Mumbo island, again to only name a few). Younger specimens occur in very shallow water hiding between stones. My crab has been caught near Monkey Bay, on a rocky bottom, with water as shallow as 10 cm/4 inches. Larger ones can be found as deep as 10 meters and perhaps even more.
Tank size: Difficult to give suggestions. I kept mine in a 33 US gals, then in a 100 US gals. Both times it was kept with Utakas, M’bunas, and other Malawi invertebrates with no detectable troubles.
Water chemistry: Follow faithfully what is stated for cichlids and these buddies will do great. This means, at the least, alkaline water (pH >7.5) and a water temp of about 24/26° C.
Spawning: No idea, and NO chance to investigate it, since I happen to have only ONE single specimen.
Food: Literally everything: sinking tablets, floating pellets, flakes (he climbs the aquascaping to catch them at surface), and plant's leaves, which I am not that happy about. Finally, it’s an excellent scavenger (see pic).
Tank Mates: All Malawians are suitable. I’ll suggest avoiding smaller fellows and/or juveniles. Also "Plecos" have not caused problems up until now.
Odd facts: While these crabs grow, their “bony-skin” will not do the same. That’s why crabs (and many other marine animals such as lobsters) change their carapax at given intervals (see pic).Personal remarks: If You plan to keep this crab beware! It’s a messy fellow, at the least. It climbs everywhere, including onto floating nests, looking for food (a sub-adult H. nyererei male over 2 inches in size didn’t survived his “visit”), bites fishes (or at least tries to), cuts/uproots plants, digs in the sand, and moves stones … DO BE CAREFUL!