Movie Profile
Due to constraints with 3D camera rigs, Aja shot Piranha in 2D and converted to 3D in post production using the reali-D conversion process developed by the company, Inner-D
from wikipedia on Piranha_3D
you dont see the cut out lines that the conversion process creates if a film is filmed in 3d. Although not as bad as clash of the titans... still not great, just annoying.