ATLANTA  Apparently eight million gallons of water and 80,000 animals were not enough for the Georgia Aquarium, which already claims to be the world’s largest. It did not have dolphins.

On Tuesday, aquarium officials announced plans for a $110 million expansion, increasing itself by 1.5 million gallons, most of which will be used for dolphin windows, dolphin shows and something called “dolphin encounters.”

But the expansion of the popular tourist attraction, which has been open for about two and a half years, will also allow Atlanta to cement its claim to the “world’s largest aquarium” moniker, a valuable bit of marketing braggadocio the Georgia Aquarium snatched from the John G. Shedd Aquarium in Chicago when it opened in November 2005.

“This is the next ‘big wow,’ ” Bernard Marcus, founder of The Home Depot and the philanthropist whose vision and deep pockets created the aquarium, said in a news release.