From what I understand, any shark needs a tank of at least 300 gallons. Sharks have to swim in order to breath properly, so they are constantly moving. A 55 standard tank is not only to small for water volume, but also for movement. Shark likely wouldn't be able to move. They also need rounded corners (achieved through many ways) so that they dont always bump into the walls. Depending on the size of the shark, it MIGHT be ok in the 180 for a few months - Im talking if the shark is like a little tiny specimen. But, 300 is really the minimum. "racetrack" tanks are the best design as well.