Oysters were regarded as a delicacy, usually eaten by the upper class. One example where they are mentioned that way is a letter by Gaius Plinius (First book, letter 15): "Audisses comoedos vel lectorem vel lyristen vel – quae mea liberalitas – omnes. At tu apud nescio quem ostrea vulvas echinos Gaditanas maluisti." Meaning: You could have heard comedians, or a lector, or a lyrist or - because of my generosity- (even) all of them. But you chose, i don't know where, oysters, pork (not literal, i don't know the english word for that kind of pork), seastars and spanish dancers (over me).

C. Plinius is using oysters as on example for upper class food, in contrast to his more simple food and more sophisticated activities.