Growing up in Guyana, I spent a lot of time on the Essequibo River and even though it flows and has a lot of rapids there are a lot of calm areas where large Aimara hang out. While fishing for Aimara there, we would catch them more in calm areas than in fast flowing areas. The biggest I remember ever seeing was about 2 and a half feet. Of course, I'm sure they're giants out there in fast flowing water though. I personally don't keep my Aimara with any flow in my tank, but that's just me.