Buying fish well is mostly a question of asking what came in

There is a settled way of talking about buying fish. It is worth asking how much of it survives contact with the detail.

Why fish goes off fast

Fish enzymes are adapted to cold water and remain active at refrigeration temperatures, so breakdown continues in your fridge. Their fats are highly unsaturated and oxidise quickly, which produces the smell people associate with fishiness.

Genuinely fresh fish smells of almost nothing, or faintly of the sea, and the strong smell is the spoilage rather than the fish. This is why buying fish is about timing rather than about brand or price.

What to look at

Clear rather than clouded eyes, red rather than brown gills and flesh that springs back when pressed are the traditional signs. Fillets should look translucent and firm rather than dull, gaping or sitting in liquid. On a counter, the fish should be on ice and not in a puddle of its own melt.

None of these is definitive on its own, which is why asking when it came in is the more direct question.

Frozen is often better than fresh

Fish frozen at sea within hours of catching is frequently in better condition than fish that has travelled chilled for days. Freezing also kills certain parasites, which is why guidance for raw fish preparations usually involves a freezing step. Domestic freezers freeze more slowly and cause more cell damage, so buy commercially frozen rather than freezing fresh where you can.

If you are short of time, defrost in the fridge and pat very dry, since thawed fish carries a great deal of surface water.

Buy what is there, not what you planned

Substituting within a rough category, such as firm white fish or oily fish, works for almost every recipe. A fishmonger asked what is best today will usually give a straight answer, and it is better information than any recipe. Whole fish is generally cheaper than fillets and keeps better, since the flesh is protected.

Asking for it to be gutted, scaled or filleted costs nothing and takes a minute.

Cooking with the margin in mind

Fish has little connective tissue, so it goes from underdone to dry in a very short window. Lower heat, or removing it early and letting carryover finish the job, is the reliable approach. The flesh going from translucent to opaque is the visual signal, and it continues after the pan.

Drying the surface thoroughly is what makes the difference between skin that crisps and skin that sticks.

Adjust seasoning at the end rather than trusting a quantity written by a stranger.

Safety and sustainability

Storage times for raw fish are short and differ by country, so follow your national food safety guidance rather than a remembered figure. Raw preparations carry specific risks and specific freezing requirements, which are set out by national authorities. Advice on oily fish intake and on mercury in larger predator species differs between countries and by group.

Sustainability ratings are published by national and regional bodies and change as stocks change, so check a current source rather than a general impression.

The takeaway

Ask what came in today, buy that, and cook it the same day or the next.

The good version is the one you can make on a Wednesday.