Ideally seed grows to about 6-15mm in the nursery rafts. At that size, the frames are dipped in fresh water to remove the flatworms and seed are stripped from the the frames in the trays, size graded and socked. A recent development has been the production of triploid mussel seed. They may prove to have significant advantages over diploids. They do not spawn so it is possible to ship all year.
Diploids stop or slow growth in winter and most available energy is diverted to gametogenesis.
As they do so their condition is poor for marketing. Triploids continue to grow through the winter, although at a reduced rate. They appear to attach more firmly to the culture ropes reducing stock losses. Triploids are also reputed to have smoother, less grainy meat. Socking The rapid growth of mussels through the nursery phase means that after three months they are ready to be socked and hung in the grow-out system.