[I gave your blend a thumbs-up, what follows is meant to be helpful. Feel free to ignore it.] I've modelled and rigged a shark or two, so I thought I'd give yours a look. Nice model, looks like some texture issues (I'd have to check references) - no big deal. If you don't have MeshLint installed, do a search for meshlint.py and install it. There are a couple of Tris at the tip of the lower jaw, don't think these can be fixed. Lots of non-manifold verts (Claspers? 2/3 along bottom edge) which can be a problem when weight-painting. [I'd guess you didn't enable 'Clipping' on your mirror modifier at the start.] You don't need to apply Modifiers to export an FBX to Unity, so I wouldn't apply them. Then there are some options for the SubSurf level. I *would* apply the Mirror mod however, a finished model *should* have some assymetry. Anyhow, thanks for sharing and feel free to take these comments for whatever they are worth.