A shark mesh i made from a simple reference image, not sure what kind of shark but still convincing.
Nice, maybe next time you should set the render dimensions to 1024x1024 so we can see the whole shark :)
Thanks for sharing.
Your 'Mirror' modifier has 'Clipping' enabled, but even so there are a few Non-Manifold vertices after applying this modifier, so a few of the edge rings in the tail must be a little bit off. Maybe scale these edge rings in only Y and Z to avoid (S Shift-X) ?
I had some fun using 'meshlint.py' to figure out the problem.