From bright eyes on a fish to closed shells on mussels—here is a practical guide to choosing fish, prawns, squid, and other seafood with confidence.
Have you ever stood in front of the fish counter wondering which fish is truly fresh? At first glance, everything looks appealing—the fish glistens on the ice, prawns are arranged in neat rows, and the mussels look as if they have just been hauled from the sea. But how can you tell if the produce is genuinely good quality?
You do not need to be a professional chef to tell the difference. It is enough to know what to look for and which signs should make you walk away.
There is one important detail, though: appearance and smell alone cannot guarantee seafood safety. Proper chilling, origin, shelf life, and storage conditions are just as important.
One of the best-known ways to check the freshness of a whole fish is to look at its eyes. In many species of fresh fish, they are clear, bright, and slightly bulging. The cornea is transparent, and the eye looks clear and well-defined.
Over time, eyes can become cloudy, sunken, or lose their natural sheen.
However, this is not a universal test. In some species, or after contact with ice and certain storage conditions, the eyes can look different. So never judge freshness by the eyes alone.
Remember: Clear eyes are a good indicator, but they must be checked alongside the gills, skin, flesh, and smell.
If you are buying whole, ungutted fish, the gills can tell you a lot about its condition.
In fresh fish, they are usually moist, ranging in colour from red to pinkish-red depending on the species. They are often described as "blood-red", but bright red is not essential for every fish.
Over time, gills can darken to brown, take on a greyish tinge, or become slimy.
A combination of darkened gills, an unpleasant smell, and soft flesh is particularly concerning.
It is worth knowing that colour is also affected by how the fish was processed and bled. That is why lighter gills do not always mean a fish is not fresh.
Fresh fish usually has naturally shiny skin, with tight-fitting scales and colours typical of the species.
The surface may be moist with a thin layer of natural slime. This is not necessarily a bad sign. It only becomes a problem when the slime is excessive, thick, sticky, and accompanied by an unpleasant smell.
If you have the chance to press the flesh, it should feel reasonably firm and springy. When pressed gently with a finger, the indentation should spring back quickly.
If the flesh is very soft, falls apart easily, or leaves a deep dent, it can be a sign that freshness has been lost.
With fillets, check that the flesh is dense, the edges are not dried out, and there is no unusual discolouration.
It might sound strange, but truly fresh fish usually lacks a strong, heavy "fishy" odour.
Its scent is mild and typical of the species. Marine fish may smell faintly of the sea or saltwater, while freshwater fish tend to have a cleaner, more neutral scent.
A strong sour, stale, or ammoniacal smell is a warning sign that the produce may be spoiled. Fun fact: The sharp, characteristic smell associated with old sea fish is partly down to trimethylamine—a compound formed when naturally occurring substances break down after catch.
Prawns are among the most popular seafoods, but they are also items where proper storage is especially critical.
Raw prawns typically have firm flesh with a translucent or pearlescent sheen. Colour depends on the species—some are naturally grey, while others are pink or reddish even before cooking.
When choosing prawns, look out for the following:
Smell: it should be mild and clean, with no harsh ammonia scent.
Texture: the flesh should feel firm, not mushy or falling apart.
Shell: it should usually be intact and fitting snugly.
Colouring: dark discolouration paired with an off smell or soft texture is a reason to pass.
Sometimes dark spots appear on the shell or head. This is called melanosis and can result from natural enzymatic processes. On its own, it does not mean the prawns are spoiled, but it can indicate a decline in quality.
Good to know: Not all raw prawns are grey. Some species are naturally pink or red, so colour alone is not a reliable test for freshness.
Checking mussels is different from inspecting fish. If they are sold live, the main thing is to check that the shells are intact and that the mussels respond to touch.
Live mussels usually hold their shells tightly closed. Occasionally, one might be slightly open. This does not automatically mean it is dead.
Tap the shell gently. If the mussel is alive, it will usually respond by closing up. Do not buy or cook mussels with broken shells, or those that stay open and fail to react when tapped.
Smell is important here too. Fresh live mussels should have a mild sea scent, not a sharp or foul odor.
When cooked, mussel shells naturally open. Any mussels that stay tightly shut after proper cooking are safest thrown away.
Keep in mind that mussels filter large amounts of water and can accumulate microorganisms or marine biotoxins. That is why controlled harvesting and trusted origins matter far more than how attractive the shells look.
Oysters are frequently eaten raw, which makes choosing them a matter of food safety. If you are buying live oysters, the shells must be intact without severe cracks. An open oyster that does not close when tapped is not fit to buy.
If you are buying shucked oysters, the meat should look plump and moist, sitting in its natural liquor. A strong, unpleasant smell means you should avoid them.
Here is something crucial to keep in mind: even an oyster that looks and smells completely fresh can carry harmful microorganisms.
Lemon juice, vinegar, and hot sauce do not sterilise raw oysters. Anyone at higher risk of severe foodborne illness—including pregnant women, young children, older adults, and people with weakened immune systems—should avoid raw oysters and other raw seafood.
Your safest option is buying oysters from a reputable fishmonger or retailer with full traceability and proper cold-chain storage.
Squid and octopus have a different structure from fish and require a slightly different approach. With squid, the body should be reasonably firm, with a smooth, moist surface and no harsh smell. Colour can range from off-white to pink or purplish depending on the species and the skin's condition.
An excessively sticky surface, strong ammonia smell, and tearing flesh are clear red flags. For octopus, look for well-defined tentacles, firm flesh, and natural moisture without any signs of deterioration.
Do not worry if the colour is not completely uniform across specimens. Cephalopods have pigment cells that naturally alter their skin's appearance.
Fun fact: Freezing octopus can actually help tenderise its texture. Frozen octopus is not necessarily inferior to chilled.
Different fish have their own unique characteristics. Here is what to look for in some of the most common species at the market.
Sea bream is a Mediterranean favourite, prized for its tender white flesh, delicate flavor, and relatively few bones. But how do you pick a truly fresh sea bream at the counter? First, check its appearance. Fresh sea bream has shiny skin, tight scales, and a firm, springy body. The eyes should be clear, bright, and slightly raised, without heavy clouding or sinking. If you can inspect the gills, look for a pink to deep red colour, free from off smells or heavy mucus.
Sea bass is another staple in Mediterranean cooking, but there are a few features to know before you buy.
One characteristic feature of sea bass is its elongated, streamlined shape. Its body is silvery, with a darker grey-green back and a pale belly. Unlike sea bream, sea bass does not have a gold bar between its eyes. When buying, check that the skin is evenly coloured, without odd spots, damage, or patches of broken texture.
Trout is one of the most popular freshwater fish, valued for its tender flesh, subtle flavor, and high protein content. Unlike sea fish, its scent is delicate, and it should never smell heavily fishy.
One of the most interesting features of trout is its skin. It is covered in a fine layer of protective slime that plays an important role in the fish's health. This natural barrier protects against microorganisms and reduces friction when swimming. A slightly slippery surface on fresh trout is completely normal. What should concern you is thick, sticky mucus paired with an off smell and visible signs of spoilage.
Turbot is a highly prized flatfish known for its firm, tender white flesh and delicate taste. It features an almost round, flattened body and an unusual eye placement that makes it easy to identify.
Fun fact: Unlike most fish, turbot lacks typical scales. Instead, the top side of its body features hard, button-like bony studs (tubercles). It lives on the seabed, where it can partially bury itself in sand, using its camouflage coloration to blend in.
How to check freshness? Fresh turbot should have a firm, springy body and naturally moist skin, free from dry patches or foul-smelling slime. Check the paler underside for unusual marks or damage. The smell should be clean and fresh, with no sour or ammoniacal notes.
Cod is a popular cold-water fish, prized for its flaky white flesh, mild flavour, and low fat content. It is most often sold as fillets, so freshness is mainly judged by appearance, texture, and scent.
How to check freshness? Good quality cod fillets should be dense, slightly moist, and have a natural white to off-white colour. Avoid pieces with dry edges, yellowing, or flesh that is falling apart. The fillet should hold its shape, and the smell should be delicate, without sharp ammonia notes.
Salmon is a top choice thanks to its tender meat, rich flavor, and high omega-3 fatty acid content. At the fish counter, it draws attention with its signature pink-orange hue, but that colour can sometimes deceive shoppers.
How to check freshness? Fresh salmon should have firm, springy, slightly moist flesh with no dried-out edges, dark patches, or bad smells. On fillets, check the structure—the muscle flakes should fit closely together without large gaps or mushy areas.
Fun fact: Salmon's signature colour comes from astaxanthin—a natural carotenoid pigment wild salmon get through their diet. Farmed salmon have this added to their feed. Therefore, a deeper orange colour does not necessarily mean a fresher or higher-quality fish.
Tuna is prized for its dense meat, rich flavour, and high protein content. Unlike most fish, its flesh often has a deep red colour reminiscent of beef. When buying, however, colour should not be your only gauge of freshness.
How to check quality? Fresh tuna should have firm, smooth, slightly moist flesh without mushy spots, dried edges, or strong odours. The colour ranges from pink to dark red depending on the species, and some products undergo processing to help retain that red hue. Bright red colour does not always translate to extra freshness.
Fun fact: Tuna contains significant amounts of myoglobin—a protein that stores oxygen in muscles and gives the meat its red appearance. This is due to the active lifestyle of these fast, powerful oceanic predators.
If not chilled properly, certain fish—including tuna and mackerel—can develop high levels of histamine. Eating it can cause scombroid food poisoning, with symptoms resembling an allergic reaction.
Crucially, once histamine has formed, cooking, baking, or freezing will not break it down. That is why relying solely on appearance is not enough for these species. Proper temperature control right from the point of catch is essential.
Many people assume fresh fish is always superior to frozen. In reality, that is not necessarily true.
Fish frozen rapidly after being caught and stored correctly can retain excellent quality. Conversely, chilled fish that has sat around too long or been kept at borderline temperatures can end up a poorer choice.
When buying frozen seafood, check the packaging. It should be intact, tightly sealed, and show no signs of thawing and refreezing.
Large ice crystals, heavy frost buildup, or items frozen together in a solid block suggest prolonged storage or temperature fluctuations, though they are not absolute proof of a health risk.
Once thawed, the fish should have a clean, light scent and a texture typical for its species.
Practical tip: If you aren't cooking the fish right away, a quality frozen product from a trusted brand is often a smarter choice than a chilled fillet with an uncertain storage history.
Even if the fish looks good, the way it is displayed matters.
A good fish counter keeps produce thoroughly chilled. Fresh fish is usually laid out on plenty of crushed ice or kept in a proper refrigerated display cabinet. There should be no strong, off-putting smells, dirty surfaces, or obvious hygiene lapses.
Check whether raw items are kept strictly separate from ready-to-eat foods.
Don't hesitate to ask the fishmonger when the fish arrived, whether it was previously frozen, where it came from, and how it has been stored.
An important distinction: delivery date is not the same as catch date. Look for clear details rather than a generic claim that it "came in today".
Picking good seafood at the shop is only half the job. Once bought, you need to preserve its quality until cooking. It's best to make fish and seafood your last stop before heading home. If you have a long journey, use a cool bag.
Put them into the fridge as soon as possible at 4°C or below, ideally in the coldest part. Store in a sealed container, separate from ready-to-eat food.
Chilled fish is generally best cooked within 1–2 days of purchase, provided the use-by date and producer instructions allow. For live mussels and oysters, follow the specific storage instructions provided by the seller; do not seal them in airtight containers or submerge them in tap water.
Always thaw frozen fish in the fridge, never out on the kitchen worktop.
For most fish and seafood, the safe cooking benchmark is an internal temperature around 63°C. Fish flesh turns opaque and flakes easily with a fork, while prawns become firm and opaque throughout.
The freshness of fish and seafood cannot be judged by a single sign alone. Clear eyes, moist reddish gills, firm flesh, and a clean scent are important markers, but you get the clearest picture when evaluating them together.
Different types of seafood have their own cues. Prawns and squid should have firm, springy texture without ammonia odours, while live mussels and oysters should have intact shells that snap shut when tapped. Remember, properly frozen fish can also be an excellent option, especially when frozen shortly after catch.
Origin, storage conditions, and an unbroken cold chain matter just as much as appearance. So don't hesitate to ask questions at the counter and check product details.
Ultimately, choosing quality seafood doesn't require specialist expertise—just attention to detail and a few good habits. Because a great seafood dish begins long before you turn on the oven or heat the pan—it starts the moment you choose what goes into your basket.
