Just thought I'd state something we already know... a 55g tank is 13" wide and those fish being discussed get 12-16" long... just saying. As a grow out tank a 55g would work, but not long term. Maybe a GT in a 55g... maybe, but the RD and Oscar need at least a 75g. The Jag as an adult needs 6' long and 2' wide to start... they are beasts!!! I would just say to get the biggest tank you can afford.