Jokes1 min ago
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To clarify the point made by Gef. ALL fish should be ok for 3 - 4 months providing it was fresh, packed correctly and stored at the correct temperature. After that time the taste and texture will suffer. However, certain fish, that are very lean, such as rockfish (rock eel) sole and flounder can be kept slightly longer, but I would not suggest more than 6 months.
All food loses some of its qualities after long storage in a frozen state, but that applies less so the lower the (constant, or else highest in the fluctuations) temperature. After all, live cells survive years of freezing in (cryogenic conditions) liquid nitrogen at near absolute zero. Part of the deterioration is due to migration of water (effectively freeze-drying to small extent) and oils/fats going off (rancid). I have stored particularly good fish for in excess of a year in a domestic freezer and found it very enjoyable at the end, although not as good as when I got it (and ate some of the same batch). The recommended maximum storage time is something else: it is arrived at largely in order to ensure merchants and other suppliers have a reliable product on offer to the public. This no more dictates a true date for uselessness than any other food expiry date (packages, tins, etc.) but instead advises the seller not to rely on it being of acceptable quality beyond this. If you have not already chucked it, keep your fish but aim to have it cooked and eaten before too long.