They are considered detritus feeders, and with the position of the mouth superficially similar to earth eaters, may prefer picking small edibles off the substrate.
The species from Lake Tanganyika T polylepis ia said to reach 18", but those are seldom seen, more likely around 10-12", I have seen some that make adult frontosa look small..
There are at least 17 other species, but those are riverine.