It is always our policy for you to follow your policies – if your housing agreements state that there are no pets allowed, we encourage you to maintain that policy. We recommend that you contact your sorority headquarters to determine what your organization’s pet policy is.
We certainly would discourage large aquariums as they can be difficult to care for properly (and in a sorority house we know that it can be difficult to enforce care for any item that is community property, without relying on the staff) and can cause considerable damage with water leaks, breakage, etc if something goes wrong. Also, without the proper attention can cause unpleasant odors.
Smaller fish bowls cause less of a concern from a potential property damage perspective, but can still be problematic in the tight spaces that make up most sorority house residential areas.