aquarium size

How big of a tank does a mangrove snapper need. Also can they be kept I fully freshwater for life.

I will be getting a custom built aquarium for my Jardini once it outgrows my 6ftLx1.5ftWx2ftH. I am currently trying to choose between a 6ftLx3ftWx2ftH and a 7ftLX2.5ftWX2ftH. Which of these two would be better?

So. I recently got into arowanas. And i started researching aquarium sized. However i live in an area without alot of aquarium activity, Like Theres some 50 ish gallons, But no big ones But anyways, My question is. Could an arowana fit in a 185gal tank? (You post sizes since i might just build...