If you really want to hear from the expert, "And all that have not fins and scales in the seas, and in the rivers, of all that move in the waters, and of any living thing which [is] in the waters, they [shall be] an abomination unto you" (Leviticus 11:10). This dietarian order is not given to Jews only. Noah knew the difference (Genesis 7:1-9), and we are all related to him.