venus clams

  Mercenaria mercenaria
(Linnaeus, 1758)

Relevant Synonyms


 drawing: Tuvia Kurz    

Shell large extremely thick and heavy, rather well inflated. Inequilateral with elevated beaks in the anterior part. Outline triangular, subovate. Sculpture of numerous concentric lines widely spaced at the umbones, closely spaced near the margins.

color : shell white or grey, sometimes with brown zigzag markings. Internallly white often stained violet.

common size : shell 60-120 mm, up to 150 mm in length when fully grown.

Mercenaria campechiensis (Gmelin) is a very closely related species that grows to a larger size and is found from Virginia to Texas.

Suspension feeder. Temperatures below 80°C have been shown to dramatically reduce clam growth. Predatory mortality during juvenile stages is a primary factor controlling recruitment of natural populations. Experiments have shown that high mortality can be compensated by warm water temperature (using warm estuarine waters) and using gravel as substratum to protect seed clams from crab predation (Summerson et al., 1995). The older-aged clams are estimated to be 38 years and sized 118 mm (Walker, 1994); suceptible to toxic algal species under bloom conditions (Bricelj, 1993).

habitat : muddy bottoms, from the intertidal zone to a depth of 10 m.

1st Mediterranean record
France, 1965 [no collecting date].

Worldwide: Canada to Florida, and Gulf of Mexico. Introduced to Humboldt Bay, California, to England and to Southern Brittany where it is well established. Mediterranean: introduced first in France, Etang de Thau (Bascheri, 1965); then in Italy: farmed in Caprolace lagoon (Roma) (Bini, 1983), Sicily, Adriatic Sea (Poutiers, 1987).

There are no recent records of natural populations along the Italian coasts. Insufficient information about its establishment success in the wild elsewhere.

speculated reasons for success :

Imported for mariculture. A first introduction to Mediterranean coast of France in 19th century, followed by a new and successful attempt, with specimens from Connecticut and French Atlantic coast.

A much-esteemed edible species. Possibly important in pharmacology: the liver and the crystalline style contain a substance capable of acting with good selectivity on cancerous cells (Schmeer, 1979).


  • Bascheri M.C., 1965. Essai d'acclimatation du clam, Venus mercenaria, en milieu lagunaire méditerranéen (note préliminaire). Rapport Committee International de la Mer Mediterranée, CIESM, 18(3): 703-714.
  • Bini G., 1983. Immissione antropica di molluschi esitici nel Mediterraneo: I°- Il lago di Caprolace. Studi per l'Ecologia del Quaternario, 5: 113-125.
  • Bricelj V.M., 1993. Aspects of the biology of the northern quahog Mercenaria mercenaria, with emphasis on growth and survival during early life history. Pp. 29-48. In: Proceedings of the second Rhode island shellfish industry Conference, Rhode island, 4 August 1992, Rhode island Sea Grant, Narraganset.


  • Poutiers J.M., 1987. Bivalves. Pp. 369-514. In: Fiches FAO d'identification des espèces pour les besoins de la pêche. Méditerranée et Mer Noire. Zone de pêche 37. Révision 1, FAO, Rome.
  • Summerson H.C., Peterson C.H. and Hooper M., 1995. Aquacultural production of northern quahogs, Mercenaria mercenaria (Linnaeus, 1758): high water temperatures in the nursery and growth penalties of predator control by gravel. Journal of Shellfish Research, 14(1): 25-31.


Last update : December 2003

©ciesm 2002