The jewel cichlid is by far the most aggressive. I have 2 in my 125 hap and peacock (yes I know they don't belong there but they are the 2nd and 3ed best looking ones I have ever seen and the best is in a mbuna tank) and I just moved everything in my tank and got rid of some fish. I also added 1 9inch Malawi Sand Diver - Fossorochromis rostratus. My 2.5 inch jewels are going after him and he is attacking back the little ones wont back down I will try to get a video.