I've been there and I must say, if any of you ever have the chance, you definitely should go. The main tank is large enough that they have whale sharks in it.
The Georgia Aquarium held the title of largest in the world from its opening on November 23rd, 2005 until March 29th this year when the Chime-Long Ocean Kingdom Aquarium opened in China. This is potentially disputable, as I could find no references to any factors other than the largest aquarium tank window. The GA Aquarium may still hold some records. As far as I know, it still is the only one in the "west" to house whale sharks. (As it turns out, was/is controversial.)
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I was unable to find information on a Japanese Aquarium under construction.
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It is important to note that the title of "world's largest" is subjective as there are many factors that should be considered. Namely, largest singular tank, largest building/complex most tanks, most creatures, most numerous of creature species, largest creatures and so on.
This was the first and only aquarium that i had been to while i was little. I thought they were all like this one. I was a tad disappointed when i went to a different one.
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I was unable to find information on a Japanese Aquarium under construction.
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It is important to note that the title of "world's largest" is subjective as there are many factors that should be considered. Namely, largest singular tank, largest building/complex most tanks, most creatures, most numerous of creature species, largest creatures and so on.