I have never heard/seen this being done and cannot imagine for a single second that it would be allowed. I suggest that you contact the customer services of your carrier and get it in writing. Since the creatures live in water - how are you proposing to bring them back on an eight hour flight with all the hours before and after that?
On a personal note, if I saw a fellow passenger attempting to embark with such cargo, I would voice the greatest possible concern to the airline.