i bought my very first around 3'' I noticed mine grew on average 1'' every two months, until it hit 12'' by that time I was feeding straight tiger prawns, after 12''
it go up to 18'' in the next year, total timing took a little over two years, my biggest problem they are very very docile even as adults, you must take very big procautions with keeping any other fish with these guys, cichlids were always a bad mixture, any catfish i put will always outgrow way to quickly, i always noticed mine would sit on top of its bottom fins and arch itself facing directly under the moving water coming right at its face, its you time it just right itll snap at anything moving in the waters current,