Pescatarian porn is a slang term for pornographic images and videos where the only completely nude participants are women.
The term pescatarian porn is a cheeky reference to a pescatarian diet which includes fish, but no red meat. Likewise, pescatarian porn does not include "red meat," a slang term sometimes used for the penis. The diet does, however, contain fish, a food often, but not always flatteringly, used to symbolize the vagina due to their similar odors.