Why would there be dead fossilized creatures created? If we believe God and that He is the creator of all things, and the record He gave of how it happened, we can put your question into perspective. Your question becomes 'how did all the fossils get here and why are some remains, such as of mankind absent?' Then we separate what we know and do not know. We know man was here from the beginning. Jesus confirmed that. We know man was created the same week as other creatures and animals. So now look at what we do not know from your question. We do not know why some creatures did and other creatures did not leave remains. We do not know that the remains we do see go all the way back to the beginning...etc. It seems to me the problem arises only when we insist on dismissing Genesis, and accepting the notion that all that exists was 'created' by itself basically and made in natural ways.
You do realize that creation is a miracle? The millions of galaxies and nebulae and stars out there, all created by what man must call a miracle. Life also. The world and sun and moon also. A mistake of unbelievers is to try to explain it all 'naturally'. There could be no such silly explanation. Nature is 'after the fact' of creation. Nature is not something we can use to tell us how it was created!
You assume that fish existed only when their dead fossilized remains are seen. Sorry, there was not a single fossil in the week of creation I would think. Yet the oceans teemed with fish and whales and etc. So then the second assumption you make in the question is that all whales and fish and etc must have left fossilized remains when they all died. The basis for that belief is unsupportable and solely rests on what happened today in nature. Nature had nothing to do with creation! There was no 'mother nature' here at all. There was nothing. No ponds. No worms. No stars. etc. I daresay we should not even assume that there were forces of nature yet. It could be that God is the force, and that this is simply manifested in various ways (forces) in whatever created reality that comes to exist including our physical reality.