What a fair price for fish actually looks like

Much of what you pay for in the fish aisle is the knife work, not the fish.

Fresh, frozen at sea, or thawed

The word "fresh" on a fish counter does a lot of work. Fish caught on a long trip may have spent over a week on ice before landing. Fish frozen within hours of being caught, then kept at −18 °C or below, can be in better condition when you cook it than a "fresh" fillet that has been in transit for days.

In many markets, fish that has been frozen and thawed for display has to be labelled as defrosted. Look for that word. Defrosted fish is fine to buy and cook, but it should be eaten within a day or two and not refrozen raw. If you want to keep it longer, cook it first, cool it, and freeze the cooked dish.

Prawns are the clearest example. Almost all prawns are frozen soon after catching, so the "fresh" ones on ice have usually been thawed. Buying them frozen and thawing them yourself gets you the same product for less, and they last longer in the freezer.

How to judge a fair price per kilo

Compare like with like. Always look at the price per kilo, not per pack, and then ask what state the fish is in.

1. 1Whole fish has the lowest price per kilo but the most waste. A fishmonger will usually gut and fillet it for you at no charge.
2. 2Bone-in steaks and skin-on fillets sit in the middle. Less waste than whole fish, much less trimming than loins.
3. 3Skinless, boneless loins and "portions" cost the most per kilo because you are paying for everything that was cut away.

A fair price is one where the trimming matches what you need. If you are flaking fish into a pie, paying for perfect squares makes no sense. If you are serving a single fillet on its own, the tidy cut may be worth it.

The two cuts that quietly outperform

1. The bone-in salmon steak

A salmon steak is cut straight across the fish, through the backbone. It keeps the bone, a ring of skin and a little of the belly, and it usually costs noticeably less per kilo than a skinless salmon loin. The bone and skin protect the flesh as it cooks, so a steak is much harder to dry out. It stays moist in a hot oven, under the grill or on a barbecue.

The bone lifts out easily once it is cooked. Roast at 200 °C for 12 to 15 minutes, until the flesh flakes and comes away from the bone, and finish with lemon.

2. The tail end of a white fish fillet

The thick centre loin of cod is the prized piece. The thinner tail end, from the same fish, is often sold more cheaply or in "mixed" packs because the pieces are uneven. It is the same fish, with the same flavour, and it cooks in half the time. For fish tacos, a fish pie, a curry or a quick pan-fried supper, where the fish ends up in flakes anyway, the tail is the better buy.

If you do want the thick loin, buy it for dishes where it is the star, and use the tail for everything else. Thick, skinless cod fillets are the right choice for a single plate. The tail is the right choice for anything with a sauce.

Getting home what you paid for

The best cut is wasted if it sits in a warm car. A few habits protect the money:

• Buy fish last and go straight home. Use a cool bag in warm weather.
• Keep fresh fish in the coldest part of the fridge, at or below 5 °C, and cook it within a day or two, before the "use by" date. That date is about safety, not quality.
• Smell it before cooking. Good fish smells of the sea, never of ammonia.
• Thaw frozen fish in the fridge, never on the counter.

You can read more about how temperature shapes quality in the cold chain, explained in plain language.

Try this on your next shop

Next time you buy fish, skip the neatest portion on the shelf. Pick up a pair of bone-in salmon steaks or a pack of cod tails, check the price per kilo against the loins, and cook them the simple way: a hot oven, a little oil, salt and a squeeze of lemon. The fish aisle and the shellfish aisle both list the price per kilo, so the comparison takes a few seconds.