Tapeworms
Got the feeling you aren’t alone in your body? You may have a tapeworm along for the ride. Animals (including you) often have a variety of internal parasites. Fish are home to several that can make the transition from fish to human.
Tapeworms enter you through either eggs or larvae that inhabit the fish’s muscles. Since you aren’t cooking it, you aren’t killing the larvae. Once it set ups shop in your guts, the tapeworm shares everything you eat.