Leviticus Chapter 11 verses 7 to 12
7And the swine, though he divide the hoof, and be clovenfooted, yet he cheweth not the cud; he is unclean to you.
8Of their flesh shall ye not eat, and their carcase shall ye not touch; they are unclean to you.
9These shall ye eat of all that are in the waters: whatsoever hath fins and scales in the waters, in the seas, and in the rivers, them shall ye eat.
10And 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:
11They shall be even an abomination unto you; ye shall not eat of their flesh, but ye shall have their carcases in abomination.
12Whatsoever hath no fins nor scales in the waters, that shall be an abomination unto you.
So, Dont eat Swine (pig for the uneducated) because its unclean. Dont eat Oysters, Clams, Mussels, Lobsters, Shrimp, or Crabs because they are abominations and you have sinned for eating such.