Northern quahogs Mercenaria mercenaria are bivalve molluscs found in the intertidal to subtidal zones of shallow, protected coastal embayments from the southern Gulf of St. Lawrence to the Gulf of Mexico. The northern quahog is an important species for both the commercial and recreational fisheries as well as for aquaculture purposes in US Atlantic coast. The management strategy of the quahog resource is largely based on the minimum legal size of 50 mm (Landry et al. 1999). At the same time, there is a growing concern regarding the sustainability of the clam industry and hence, an evolving interest in stock enhancement. Effective brood-stock management, however, requires basic information about the animal's reproductive biology (DFO 1996).