i agreeWarrendaFish;4781516; said:My female dempsey (4" at the time) spent about 6 months in a 125 with my full grown male Oscar without problems.. He chased her around at first but they became friends after a little while.. My male Oscar is quite aggressive, but so is the female dempsey.. IMO it would depend on the individual fish's personality. Try it out, but have a way to seperate the 2 if need be