A couple years ago I was flying dtw to NYC. The inbound was from BOS and already late coming in and they delayed boarding because the cabin smelled of fish. Someone had apparently checked fresh fish from Boston and not sure what happened but something happened on the inbound flight and the cabin reaked of dead fish. As we were boarding the smell was almost unbearable and the pilot assured us that once we were airborne it would be better (and it was) and said the smell was a lot worse a few minutes before boarding.