Helpful Hints from joeeze: Does freezing fish kill bacteria?

Short answer shorter: No.

"Freezing fish will NOT kill bacteria! Freezing at very low temperatures does kill fish parasites, which is one reason why maatjes herring and much fish for sushi and sashimi are frozen before being eaten raw. But bacteria are hardy and will spring back to life when you thaw the fish."

[via Harold McGee and the New York Times]