The characteristics of the clam ground substrate on both sides of the Bach Dang estuary is usually muddy-sand formed by the interaction between tidal and river flows. The medium flow receiving the rich nutrients from land created the tidal flats which were suitable for the clam growth. Thus, there were the special features in the process of clam culture in the Bach Dang estuary which differed from the other areas to fit with the flow and hydrochemistry characteristics in the area, such as size of breeding clam and time for stocking. The growth of clam correspondence between age and size of the shell is determined by the formula: y (months) = e C +0.7455/1.025. The growth stages of clam had been affected by the environment variations, so the clam growth indicated for the changes of environment.