What would happen to a living organism, say a fish for example, if every single strand of DNA in it, and on it as in including everything living in and on it like parasites, bacteria etc was instantly torn to shreds say by powerful radiation or something like it, and no new living things like bacteria etc was allowed to come in touch with the fish after this event?

Would it die instantly? Would it's body decay? Would it turn into organic goop? What happens to flesh/biomass when no organic activity can act on it?
Genuinely curious.