you can keep fish up to 10" in a 55. as long as the tank is wider then the fish is long, theyll be fine, but you will need to upgrade eventually. im so sick of people saying you need a 125g for a single fish that will EVENTUALLY grow to 16"+.
TANK SIZE IS REALITIVE. if you have a 3" great white shark. you can keep it in a 10g tank untill it grows out. you dont need a 700,000,000g tank for it at 3". (not to be taken literally, but i hope at least a few people will get the concept)
minimum tank size requirements are set for FULL GROWN FISH, so, unless your fish is full grown, the numbers dont apply to you.