In regards to food, fresh is used in a number of different ways. It can mean not stale, as in fresh bread, but it is also used in regards to meat, vegetables, or fruit. People talk about having fresh fish, but how would they say that they have un-fresh fish?
closed as not a real question by MetaEd, JoseK, tchrist♦, cornbread ninja 麵包忍者, Robusto Mar 27 '13 at 0:03
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It really depends on how "unfresh" it is. If the fish has not been preserved, then it is simply rotten; but if it has been frozen, then it is still considered "fresh" but "frozen". Vegetables and fruits would also fall under the "old," rotten," "passed their prime" or "aged" categories; that is, unless they are canned or frozen.
I doubt that there is such a word. However, there are many variations of calling things "not fresh" so to speak. Here is a list: old soiled musty rotting hackneyed tired However, the word @stale@ that you mentioned is, in my opinion the best word although it might contain a few grey areas