He has a Ph.D. and wears a labcoat, but what kind of Medical education did Dr. Zoidberg have?
Zoidberg is supposed to be a doctor of medicine, and acts as staff doctor for Planet Express, despite his
"woeful understanding of human physiology and allusions to his questionable credentials."
He claims to be an "M".D. (see below),but states in A Clone of My Own that he (ahem) misplaced his medical qualifications
Cubert: As long as I'm going to be in charge here, let me examine my so-called "crew", if it can so be called. First of all, Dr. Zoidberg, do you even have a medical degree?
Zoidberg: I lost it ... in a volcano.
However, he later states in "The Duh-Vinci Code" that his doctorate isn't in medicine at all
Zoidberg: Maybe da Vinci painted over something else. It's called a pentimento.
Farnsworth: That's true, Dr. Zoidberg. How did you know that?
Zoidberg: My doctorate is in Art History.
As noted in the episode "The Duh-Vinci Code", Zoidberg has his doctorate in art history.