Cells slowly frozen, the temperature band between 0 degrees - -5 degrees below zero is called the ice crystal generation zone, in this temperature zone, the water in the animal cells will be a large number of crystallization, piercing the cell membrane, resulting in a large loss of cellular tissue fluid in the process of thawing food. So it looks like the meat becomes rotten.

Seafood that's really rotten can breed Vibrio enteritidis in abundance. Don't eat it if it's not very fresh. If you don't smell it, it's also recommended that you cook it thoroughly before eating it.