What is the ruling on one who swore not to eat meat, then ate fish?

If a person swears an oath not to eat meat, he does not break his oath by eating fish; this is because common usage does not refer to it as meat, even though the Quran calls it meat in the verse: "And He it is Who has subjected the sea (to you) that you may eat therefrom fresh tender meat" [An-Nahl:14]. This is because the Quranic designation here does not entail a legal ruling.