If an animal living in the water doesn't have fins and scales then it is not food. Unclean items are scavengers. They eat trash. You are what you eat you know. In the Hebrew and Greek the Bible never once calls an unclean item, food. The idea is for good health. 1 Peter 1:16 is a quote from the Health Laws. If you want to be what 1 Peter mentions then you must follow the context of its original quote.