I have no clue as to which specific organism is targeting your dead YP in such a fashion. (Hopefully, the experts will know.)

However, almost everything that eats carrion in the wild, starts on the easiest parts. Especially for any larger animal with tough skin, hide, scales, etc.

Crows, gulls, and other birds will start on the eyes. Four-legged carrion eaters in North America or the African plains will start on the excretory soft parts of big game, as you noted on your fish.

I will definitely come back to your thread to learn what the consensus says on your poor YP. I hope the rest of your YP can survive through their stress period!