most of my fish i do get as groups of 4 or 5, then after a while some die off leaving only one or two, then i get a bunch of another species. this tank has been running for years, thus the danios are the oldest, i think, then the rainbows next, the tetras are the youngest. although i admit i only got two tetras, not a group, but that was because they where sale price and there was only two left that where healthy. The danios and the rainbows seem to like to school together and as for the gourami....., i dont even know how long ive had it, again it was listed as a "dwarf" gourami at the store, until it grew then i researched found it was a gold gourami, it had been sold in the wrong tank. i think i should stop buying things at my local fish store that are listed as "dwarf" lol most of the times they turned out not to be.