Cooked fish keeps less well than meat, and how much less depends on how oily it is.
That is the whole logic here, so it is worth going by type.
White fish — 3 days
Cod, hake, pollock. The longest keeper among cooked fish, because there is little fat
to oxidise. Freezes for three months.
Oily fish — 2 days
Salmon, mackerel, herring. The fats oxidise quickly, and oxidised fish fat is exactly what
people mean when they say something tastes “fishy”.
Worth knowing: at first this is a flavour problem, not a safety one.
The fish goes unpleasant before it goes dangerous — which is why airtight storage,
by limiting contact with air, buys you a real difference.
Battered or breaded — 1 to 2 days
The coating goes soft within hours and the whole thing reheats badly.
Do not freeze it cooked.
In sauce — 2 to 3 days
The sauce limits air contact, which slows the oxidation that shortens everything else here.
Freezes two months.
Fish soup — 1 to 2 days
The shortest of all, and not a freezer candidate: the fish falls apart and
any prawns turn rubbery.
Smoked fish, opened — 3 to 5 days
The longest on the list, because smoking and salt do part of the preservation work already.
Freezes two months.
What applies to all of them
Airtight, always. Fish both gives smell to everything around it and takes
smell from everything around it. A sealed box, not a plate under film.
Cool it fast and get it in within an hour. Fish moves from fine to off
faster than any other cooked protein.
Reheat low and covered — 150 °C under foil is gentlest. Honestly,
cold cooked fish is often better: flaked into a salad, a sandwich or fishcakes,
it avoids the problem entirely.
When to bin it
A sharp ammonia note, a slippery surface, flesh gone dull and grey.
With fish, err early — it is the one protein where waiting to be sure is a bad strategy.
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