The best pure seafood play is probably Street and Company although most restaurants have seafood on the menu. For a nice, not too fancy piece of fish, I also like The Old Port Sea Grill - pretty straight forward fish. Veggie - once again a pure play (all vegetarian) is The Green Elephant on Congress St. I am about as far from a vegetarian as one can get and I love the place.
Old Port Cafe
111 Main St, Winterport, ME 04496