Very rare in the wild, and difficult to get in captivity (at least the genuine species).
They are sort of a riverine sifter. Similar to rostratus, robertsoni, etc. Aggression is similar to their close cousins, i.e. lots of threatening without much murder.
Being riverine in origin, they are more demanding of water quality. Since they sift through detritus in the wild, they also need some vegetable matter in their diets (which can be obtained with an good pellet like NLS that contains lots of algae). Food particles MUST be small for them to be able to feed slowly and gradually. They will not do well with big aggressive eaters unless those species are offered floating foods (the rhytisma will not likely feed from the surface -- they will much prefer to sift from the substrate).
The presence of sand in the tank is important for their comfort level as it allows them to behave naturally. If the sand is sifted out their gills (rather than being spit out) it is the right size. There can be some larger particles mixed in, but sand needs to be present.
These fish can be a touch shy at first, especially since they are not captive bred for generations on end. They do well with a shoal of livebearers or other fish which will make them feel more comfortable. You definitely do NOT want to mix rhytisma will some of the thuggish cichlids (citrinellus and the like) except in a very large tank.
The best setup, in my opinion, would be to mix six or seven rhytisma in a very large tank (125+) with a ton of livebearers or large tetras and a cat or two. I would not crowd them at all since it increases intra-species aggression. A pair could get along in a mildly aggressive community situation.
I have a beautiful pair right now. Welcome to the club!
