[Jim Sachs]

In order to use real-time lighting effects, each polygon or vertex must have a surface normal, which is like an arrow pointing straight out, perpedicular to the surface. These are used for shading, reflections and speculars (shine).

When a fish mesh bends, its vertex normals no longer point straight out from the surface, so I recaculate each vector. Though technically correct, the differences in shading are so slight that most people don't notice them, so the calculations are now turned off by default.