Churaumi Aquarium, Okinawa
If you want to see a really impressive aquarium, Okinawa's Churaumi Aquarium is the place. It's the third largest aquarium in the entire world (only beaten out by the Georgia Aquarium in the States, and the Dubai Mall Aquarium in the United Arab Emirates). Fun fact: the aquarium was the largest in the world at the time it was built, and was named Churaumi through a public vote - Chura means beautiful in the Okinawan dialect, and umi means ocean in Japanese.
Churaumi Aquarium has a total of 77 tanks over four floors - and you'll see everything from deep sea creatures to sharks as well as coral and tropical fish. Okinawa really does make for a great location to appreciate just how beautiful the sea is, with so many amazing beaches and great snorkelling and SCUBA diving too.
Osaka Aquarium Kaiyukan
Situated in a really cool building (for those of you that are into neat architecture!) the Osaka Aquarium has a range of different marine life habitats on display, all from the Ring of Fire region of the Pacific Ocean. The aquarium suggests that seeing all the displays takes about two and a half hours. The permanent displays include area of the world like Antarctica, the Great Barrier Reef, Monterey Bay and the Aleutian Islands. It's fascinating seeing all the different marine life from different parts of the Pacific Rim.
For more information about their displays, admission fees and opening hours, head over to their website here.
Hakkeijima Sea Paradise, Yokohama
This place really is a Sea Paradise - not only does the area feature the aquarium, but also has a hotel, a shopping mall, and amusement park rides, too! Hakkeijima's aquarium setup is done in different zones - one thing that is particularly cool here is that as well as all the amazing marine creatures you can see, they also have an area dedicated to flowers of the sea. If you need to pick up souvenirs for little ones on your trip, they also have a great gift store here with the cutest plush toys!
For more information on visiting Hakkeijima Sea Paradise, check out their website here.
Hopefully some of these options will help you not only enjoy your time in Japan but also to appreciate all the amazing things that the sea brings us.