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Carpet shell clam:professional buying guide, grooved or Manila clam, size, health areas

Carpet shell clams for the trade: grooved or Manila clam, minimum sizes, Arcachon and the Gulf of Morbihan, health classification of areas, sizes, substitutes.

Updated 7 min readLiveCriée editorial team

Contents
  1. Buying sheet
  2. Grooved carpet shell or Manila clam: how not to get it wrong?
  3. Health areas and closures: what to check?
  4. When to buy carpet shell clams?
  5. How to check a lot of carpet shell clams?
  6. What to replace carpet shell clams with?
  7. What makes the price of carpet shell clams move?
  8. Frequently asked questions

The carpet shell clam (palourde) is a burrowing bivalve shellfish, sold alive, and two species share the French market: the grooved carpet shell (Ruditapes decussatus), the only one allowed to be called simply "palourde", now rare, and the Manila clam or Japanese carpet shell (Ruditapes philippinarum, "palourde japonaise"), introduced for farming in the 1970s, today the most common in Europe, and dominant on some Atlantic beds such as the Arcachon basin. Hand-gathered or farmed, it can only be sold if it comes from a classified production area, and it travels with a health label.

Buying sheet

Carpet shell clam
Scientific namesRuditapes decussatus (palourde, known as grooved carpet shell or European clam); Ruditapes philippinarum (palourde japonaise, Manila clam)
SeasonNo marked national season: supply follows the open beds, the fishing calendars set locally and the health closures
Closed seasonNo EU closure. Licences, periods and reserves set bed by bed (in the Arcachon basin, two reserves closed to fishing since 2016)
Minimum sizeGrooved carpet shell: 40 mm in the Atlantic and the English Channel, 3.5 cm in the Mediterranean (France). Manila clam: 35 mm, 32 mm in the Arcachon basin, 4 cm in Normandy (former Lower Normandy)
Size grades on price lists (examples of trade practice, not a standard)Medium, large, very large; by the kilo, in 3 kg packs or in trays; mention "caught" or "farmed"
Main fish auctionsNot applicable: the carpet shell clam does not appear in the FranceAgriMer report on auction halls, it is sold outside the auctions
OriginsFrance: Arcachon basin, Gulf of Morbihan, other beds in the English Channel and the Atlantic; also farmed in Italy, Ireland, Portugal, Spain and the United Kingdom (FAO)
Production methodsLicensed commercial hand gathering (cockle and clam permit, "timbre coques et palourdes"), farming (clam farming, "vénériculture")
YieldAbout 18% of flesh for the Manila clam (FAO, provisional value): measure it on your own deliveries
StorageAlive, kept cool and dry: once packed, it must not be re-immersed or sprayed with water (Regulation (EC) 853/2004); in its original packaging with the health label

Minimum sizes: Regulation (EU) 2019/1241, Annexes V to VII and IX; French order of 28 January 2013, consolidated version. Yield: FAO, Fisheries Technical Paper No 309 (1989).

  • 153 tof carpet shell clams fished in the Arcachon basin in 2023, against 1,028 t in 2007
  • 99%Manila clams on the Arcachon bed in 2024
  • €38Mof carpet shell clams and other venerid clams exported by France in 2024

Source: Ifremer, Arcachon basin monitoring 2024; FranceAgriMer, Key figures 2024, based on French customs data.

Grooved carpet shell or Manila clam: how not to get it wrong?

  • The label decides. The commercial designation and the scientific name are mandatory (Regulation (EU) 1379/2013). In France, "palourde" means Ruditapes decussatus; Ruditapes philippinarum must be sold as "palourde japonaise". If a price list says "palourde" without further detail, ask for the scientific name.
  • The shell gives clues. The grooved carpet shell has an oval to almost square shell, clearly cross-hatched in an X pattern at the back, cream to light brown in colour. The Manila clam is more broadly oval, with radiating ribs that form small bumps at the edges, and very variable colours, from white to bright brown, often striped or zigzagged with brown (FAO).
  • These are only clues: the two species hybridise in the wild (FAO). The label is what counts.
  • The scarcity is real. In the Arcachon basin, the grooved carpet shell accounted for only about 0.5% of carpet shell clams in 2024 (Ifremer). The Manila clam, hardier and faster-growing, now supplies most of the carpet shell clams produced in Europe (FAO).

Health areas and closures: what to check?

Every area where shellfish are farmed or fished for sale is classified by prefectoral order, on the basis of microbiological and chemical analyses. The carpet shell clam, which lives buried in the sediment, is classified with the burrowing bivalves, separately from oysters and mussels: the same area can be good for oysters and more contaminated for clams.

ClassWhat it allows
Adirect placing on the market
Bsale after purification or relaying
Clong-term relaying or heat treatment
Not classifiedprohibition

Source: DIRM Sud-Atlantique, 2022 Atlas of the sea and coast, sheet "Les classements sanitaires conchylicoles" (health classifications of shellfish areas).

On top of this classification come temporary closures. When algal toxins exceed the regulatory thresholds in shellfish (Ifremer's REPHYTOX monitoring), or after pollution, the prefect takes measures on the contaminated area: fishing and sale of its shellfish stop, sometimes overnight. A toxic episode is only considered over after two consecutive weeks of results below the thresholds. For the buyer, this means supply that can disappear from one origin for several weeks.

When to buy carpet shell clams?

The carpet shell clam has no marked national season: it is sold all year round, depending on the open beds. Supply depends on the fishing calendars set locally (licences, periods, reserves), health closures, and the state of the beds. In the Arcachon basin, catches fell nearly sevenfold between 2007 and 2023, and the exploitable biomass recorded by Ifremer in spring 2024 was the lowest of the series. Spawning takes place mainly in summer (FAO).

How to check a lot of carpet shell clams?

  • The health label: identification mark of the dispatching establishment, species (common name and scientific name), packing date. The retailer keeps it for at least 60 days after splitting the lot (Regulation (EC) 853/2004).
  • The shells: closed, or closing firmly when touched; no broken shells.
  • The weight: a live clam is heavy for its size.
  • The smell: of the sea and fresh. Open, unresponsive clams are thrown away.
  • The sand: as a burrowing shellfish, the clam may contain some; plan to purge it before use.

What to replace carpet shell clams with?

UseSubstituteNote
Pasta, sauce, marinièreCockle, hard clam (clam)burrowing shellfish, also need purging of sand
Stuffed, gratinatedWarty venus clam, large Manila clamsolid shell for the oven
Platter, rawWarty venus clam, dog cockle (amande de mer)served raw on platters

What makes the price of carpet shell clams move?

The carpet shell clam does not appear in FranceAgriMer's auction sales statistics, and no recent public series of first-sale prices makes it possible to put figures on its national seasonality: this section remains qualitative. Above all, remember that the price on a price list is not the fisher's price: sorting, possible purification, packing, transport and margin are added to it.

  • The state of the beds: when a large bed such as Arcachon sees its exploitable resource shrink, French supply tightens.
  • Health closures: a closed area takes part of the supply off the market overnight, sometimes for several weeks.
  • The species: check which one is invoiced; the grooved carpet shell has become rare.
  • The size: large and very large clams, sought after for stuffing, generally sell for more per kilo.
  • Exports: part of French production goes abroad (€38M of carpet shell clams and other venerid clams exported in 2024).

Frequently asked questions

What is the difference between palourde and palourde japonaise?

They are two species. The palourde, or grooved carpet shell (Ruditapes decussatus), is the native species, now rare. The Manila clam (Ruditapes philippinarum, palourde japonaise), introduced in France in 1972 for farming, has settled in the wild and today dominates some Atlantic beds, such as the Arcachon basin. In France, only the first can be sold under the plain name "palourde".

What is the minimum size of a carpet shell clam?

In the Atlantic and the English Channel, 40 mm for the grooved carpet shell and 35 mm for the Manila clam (Regulation (EU) 2019/1241). Exceptions: 32 mm for the Manila clam in the Arcachon basin, 4 cm for the Manila clam fished by professionals in Normandy, and in the Mediterranean 25 mm under the EU rule, 3.5 cm for the grooved carpet shell under the French rule.

Where are the carpet shell clams sold in France fished?

On the beds of the English Channel and the Atlantic, the two best known being the Arcachon basin, where they are gathered by hand at low tide, and the classified bed of the Gulf of Morbihan. They are also farmed, in France as in Italy, Ireland, Portugal, Spain and the United Kingdom.

Why can a clam area close overnight?

Because shellfish filter the water and concentrate what it contains: bacteria after heavy rain, algal toxins during a bloom. When analyses exceed the regulatory thresholds, the prefect takes measures on the area, and fishing only resumes once the results are back below the thresholds.

How much flesh does a kilo of carpet shell clams give?

About 18% of the weight for the Manila clam, according to a provisional FAO value. The flesh content varies with the season and the origin: weigh your shucked clams to set your yield.

Sources

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