I've got 3 in my 50 gallon. Also never see them. They're about 10-13 yrs old, and about 5" ( I'm talking length here) they are the fattest fish I've ever had, they get huge around and at least for me have been safe with all other fish, and I've got a school of rasbora espie in that tank. I also have a large pleco so do a lot of night feeding, spirulana wafers, shrimp pellets, plankton pellets, and tetra min. Two of mine pile in one log and the 3rd in another, but it may be that all three would't fit in one. Mine are the spotted ones and I think by looks I've got 2 different kinds or sexes.