Last time I went to the aquarium (over a year ago), I had decent results (decent, not great) with the 35/1.4L...that was at f/1.4 on a 5DII, where ISO 3200 was ok for me.

Quite a while back, I took a T1i/500D and 17-55/2.8, with results that weren't very good (except when the subject was my daughter and I used a 430EX II to light her).