Churaumi Aquarium is definitely superb, far more huge fish than Kaiyukan in Osaka, but it's not in Naha city, not even near the city.
If you drive a car it takes two hours from the airport, and if you take a public bus probably more than three hours for one way. Even though day-trip to Naha is feasible, to Churaumi in Motobu-town is pretty difficult or I'd rather say almost impossible.