Alisa Weilerstein, one of today's top cellists, is accustomed to playing in the world's finest concert halls. This season alone brings her to Seoul, Hamburg, Los Angeles, London and Sydney. But there was one other lofty venue on her travel schedule: the National Aquarium in Baltimore. Strategically positioned above a tank full of stingrays, Weilerstein unpacked her cello to serenade the sea creatures — and dozens of pleasantly surprised aquarium visitors — with music by Johann Sebastian Bach. She chose the Prelude from Bach's Suite No. 5 for unaccompanied cello. The music's tranquil power and meandering melodies became an extraordinary soundtrack to the majestic rays as they roamed through the water, rising occasionally to catch a note or two.