single female a 125 gallon would be adequate- 15-16"
single male a 180 gal 6'x2' absoultue min and better yet a 240 gallon 8'x2'. 20-22"+
temporarily will not be more than a year or a tad bit more, they grow fast and are very active fish. anywhere from 8-10" they should be moved. I would advise not to buy the fish until you have the proper housing setup, in case down the road you can't provide suitable housing, this happens to many hobbyists looking at dovii.