F5 and MV,
Thats exactly what causes that is rigor mortis.Did the fillets actually tear apart?MVs icing for two days is actually very common practice with some comercial guys.All that realy matters is that the fish is kept cool through this proccess{ice}.Also never straighten out a fish that is stiff in the cooler with r-m it tears the meat and ruins the flaky texture.

We used to have to wait for the p-cod up in AK to go through R-M before we could start fillett them.We used to do them too fresh and the fillet would actually twitch afterwards.Kinda freeky to see a fillet twitching like it is still trying to get away.