My Midas was purchased in October 2009. He put on the most size for the first 3 months and went from 1.25" to 4.5" during that time. I was also feeding him very heavily on earthworms and omega one. Since I got some bulk on him I slowed down his growth pace a little by feeding a little more conservatively. He is now about 7.5 months old and around 6.5" - 7". Of course its only a guesstimate since he moves around so much. So I think your fish seems to be growing at a very nice pace.