That iconic theme, you probaly heard in many hollywood movies ranging from Beauty and the Beast to Hellraiser. Uploaded it here, so you notice the awesome archive with classical music. It is used for anything but aquariums. The license is EFF OAL, which is equivalent to CC-BY: credit the archive, the performers, link back to the work, and you should be okay. Camille Saint-Saens was 19ie century composer, so the score itself should be public domain.

http://www.ibiblio.org/pandora/HOMEPAGE.html

Pandora Records was established in 1973. The business was active for over ten years, finally succumbing when the LP died because of the CD. The master tapes (and LPs when tapes were missing) have been archived; in addition, there is a contrib directory for other items, a small part of the University of Washington's music archives, some music of Sir James Galway and some archives of the Advent Chamber Orchestra.

Downloads are redirected to a high speed server at "Ibiblio" owned by the University of North Carolina. There is also a mirror. The archive at hebb.mit.edu no longer exists.

This archive is available for free download subject to an EFF license.

http://web.archive.org/web/20120408152205/http://pan.zipcon.net/EFF/oal....

The Original Author retains the copyrights to works released under this license, but grants the worldwide public permission to use the work in the ways authorized herein. Activities other than those specifically addressed below are outside the scope of this license.

    Access, Reproduction, Distribution, Modification, and Performance Rights. Subject to the terms and conditions of this license, the Original Author irrevocably and perpetually grants to the public authorization to freely access, copy, distribute, modify, create derivative works from, and publicly perform the work released under this license in any medium or format, provided that Original Author attribution be included with any copies distributed or public performances of the work, as well as any derivative works based on the work, as further described below.
    Original Author Attribution Requirement. Original Author attribution is generally defined as a method in the regular course of dealing that reasonably conveys to the recipient of a copy or performance the following information: (1) The notice "(O)" that indicates the work is released under the EFF Open Audio license; (2) the identity of the Original Author; (3) the title of the work (at Original Author's option); and (4) how the first listed Original Author may be contacted (at Original Author's option).