Manila clam (Ruditapes philippinarum) culture in oyster bags: Influence of density on survival, growth and biometric relationships

In order to establish the suitability of oyster bags as a method for Manila clam culture, Ruditapes philippinarum (Mollusca: Bivalvia), five batches of clams (mean live weight 0.55 g) were placed on the ground in the intertidal zone of Eo Estuary in March 1993. Four batches were sown in bags at different densities (100, 250, 500 and 1000 clams per bag) and one sown at 160 clams per m(2) in sand-gravel bed covered with plastic netting. In August 1993 and April 1994 all batches were picked up and survival, live weight, length, height and thickness recorded. Survival of clams at the highest density was significantly lower than survival at lower densities in August 1993 (60.5%) and April 1994 (26.7%), but no differences were found among the other treatments. Ln addition, we found differences in growth between sets in both dates, with the best growth in the lower densities and reduced, density-dependent growth in the bags. Biometric relationships were also affected by density at the end of the experiment. High density had a greater influence on reducing shell height than on length or thickness. It was concluded that traditional ground culture in Europe is, from both the biological and the economical viewpoints, more efficient than oyster bag culture. However, oyster bags may be useful for temporary storage or as nursery system for clams.