Buy from the quay and ask the right question

The best fish supper begins with a question: what came in today? In small harbours and estuary markets, the answer changes with the tide, the weather and the week. A chalkboard that has been rubbed out and rewritten twice before noon tells you more than any recipe book. Ask what is plentiful, what is cheap because there is a glut, and what the person behind the counter would take home for their own tea.

Locally landed fish has usually travelled a few miles rather than a few days, and it shows. Mussels from a rope-grown bed, mackerel taken on a handline off the headland, flatfish lifted from the sandy grounds a mile offshore — these are foods with a short history between water and plate. The old fishing quarters knew this instinctively. When the boats were in, the whole town ate what the tide had given it, then waited for the next tide.

If you are buying whole fish, look for bright, bulging eyes, red gills and skin that still feels damp and slippery rather than dry. Ask for it gutted and iced. For shellfish, smell matters most: fresh mussels should smell of the sea, not of ammonia.

A rough guide to the seasons

Nothing is fixed, because water temperature and weather shift everything by a few weeks, but a rough calendar helps you know what to hope for.

• Spring: crab comes into its own, cockles are gathered on the estuary flats, and the first mackerel start showing along the south-west and west coasts.
• Summer: the great mackerel months. Plaice, dab and lemon sole are at their best, along with squid in the south and mullet in the harbours.
• Autumn: mussels improve as the water cools, lobsters are still good, and bass move inshore where local rules allow.
• Winter: mussels and oysters are at their finest, and dab, whiting and skate appear in the colder months. The old "R in the month" rule for oysters is a decent memory aid, though well-managed farmed shellfish is available all year.

Mussels: ten minutes on the grill

Rope-grown mussels arrive clean and need little more than a rinse. Rinse about a kilo in cold water, pull away the beards, and discard any with cracked shells or any that stay open when tapped. If they will not close, they are not worth the risk.

Set a deep roasting tin or a sturdy pan on the grill over high heat with a knob of butter, a chopped shallot, two cloves of garlic and a glass of dry cider or white wine. Tip in the mussels, clamp the lid on, and cook for four to six minutes, shaking the pan once or twice, until the shells open. Throw in a handful of chopped parsley and serve with bread. Discard any that remain shut. The liquor is the best part — do not let anyone tip it away.

Mackerel: cook it the day it arrives

Mackerel is cheap, abundant in summer and unforgiving of delay. Ice it as soon as you can; if you are catching your own, bleed and gut it straight away and keep it in a cool box, never in a warm bucket. Fillet it, score the skin a couple of times, rub with oil and a little salt, and lay it skin-side down on a hot grill. Leave it alone for three or four minutes — no flipping — until the skin blisters and the flesh turns opaque and flakes. Lemon, mustard, or a spoon of horseradish cream is all it needs. Overcooking turns it dry and grey, so take it off early.

Flatfish: plaice, lemon sole, dab

Flatfish suit the grill beautifully if you use a hinged basket or a well-oiled grid and keep the heat high. Score the dark side of a whole plaice or lemon sole two or three times down to the bone so the heat penetrates evenly, brush with oil, and season. Grill three to four minutes per side, turning carefully with a fish slice. Dab is the underrated one — small, sweet and often very cheap. Serve with brown butter, capers, lemon and new potatoes, and check the thickest part near the head flakes cleanly before you take it off.

Safety, rules and keeping it fresh

Coastal eating is a delight, but a few habits keep it safe. Check local notices before gathering shellfish: algal blooms can close beds with little warning, and taking from a closed area is both illegal and genuinely dangerous. Only collect where you have permission, respect minimum sizes and local byelaws, and never take more than you will eat.

• Keep fish and shellfish cold, on ice, in a cool box, well away from cooked food.
• Cook shellfish thoroughly. Avoid eating them raw unless they come from an approved, labelled source.
• Discard cracked shellfish and any that stay shut after cooking.
• Wash your hands and boards after handling raw seafood, and keep raw and cooked apart.
• Return undersized fish gently and quickly, and leave spawning fish alone.

Eat with the tide and the calendar rather than the supermarket shelf. Ask, taste, and cook simply — the flavour is already there, and the shortest journey from harbour to grill is the one that tastes best.