Molly Walker, director of leasing and marketing for the Beal Cos. LLP, the building's owner, tells GlobeSt.com that the aquarium, which has been in the class A, 76,000-sf 177 Milk St. property for about 10 years, will also give up some third floor space in 2006 as part of the agreement.

Although she declined to discuss terms of the lease, space in the building, which is 100% occupied, rents for $24 per sf, according to a listing on Beal's website. Constructed in the early 1892, the Grain Exchange Building was originally built on land donated by streetcar magnet Henry M. Whitney. It was developed as a meeting place for the Boston Commercial Exchange and the Boston Produce Exchange, which eventually became the Boston Chamber of Commerce.