for about 15 yrs now, i have always had Goldfish and tropican fish as well as chichlids all in the same tank, lol. i've never had a problem, i just make sure i don't get any real big tropical fish. Right now i have 2 catfish one is about 8 inches long, I also have about 3 goldfish ranging from 5-9 inches and a coi fish, I have about 3 different kinds of guppies, and many many more to list, not sure of the names i keep the water temp around 71 degrees, i never have any problems, they are not stressed out, they do not fight, i have a 55 gallon tank and have many plants and logs for the fish to hide in, but they don't use them, only the catfish and the barb fish stay in them.