There is a rumor of a whale on Animal Crossing it is said to be out at sea and is a VERY rare sighting. I know what your thinking, "This guy's crazy", right? Well go to this website for PROOF and it also has other cool rumors and tells whether they are true, fake, or still just a rumor. However, to back up BubbaT, there are no sharks. That's in Animal Crossing: Wild World for the Nintendo DS.
This website here:http://www.freewebs.com/acrs/animalcrossingrumors.htm