I had the same question as a while ago, i also have read that they are fast growers. I had 3 uaru in a 135 gal tank with 6 gold severums (5 of them were male) I got my uaru a when they were around 1.5 inches. After spending 7 months in the tank with the severums, my largest uaru was only 4 inches at the most. I ended up removing all the severums, raised the tank temp to 28c from 26c.They were on a diet of Hikari cichlid gold, romaine lettuce and freeze dried blood worm, but now i feed Hikari Excel, Hikari discus bio-gold, romaine lettuce and froozen blood worm. Now my largest uaru is a solid six inches and still growing. I only removed the severums 2 months ago, and changed there diet at the same time and got a little more than 2 inches of growth in that short time. so now my uaru are 9 months old and i would say that i got them to this size by first making them more comfortable in the tank by removing all the severums, raising the tank temp and changing there diet. Im not sure which one did it but they have grown alot in the last 2 months.