Good info from Wes in post #29.I was a little confused at some of what was written down near the bottom though....I currently have a near twelve inch armatus in a 180 and it has been there since it hit six inches about a year ago,and before that,it was raised from three inches in a much smaller tank.I think the armatus is the fastest growing fish in the group that you have mentioned, or possibly a tie with the dorado, but there are many variables that will affect it's growth rate. If it is kept alone,as part of your question,it could possibly hit two feet within a year,if water changes are strictly kept up and good food is offered..If it is kept with other fish,it may not become the apex dominant fish,as is the case with mine,it answers to a bigger,meaner,widebar datnoid which I suspect inhibit's the armatus' growth...I have a three hundred gallon tank waiting for me to get around to setting up and it will be the eventual home of the armatus.It will not have to compete with and be chased by the dat so I expect it to put on a little more size....I have kept dorado in the past and much of what I already said applies to them as well.The dorado is a much more active fish and can be more aggressive when it starts to grow to a decent size.