A method of growing shellfish is disclosed. The method comprises obtaining a support tray (I) with recesses (7) where at least some of the recesses (7) incorporate means adapted to create a deliberately formed alphanumeric, written or pictorial mark on the shellfish as it grows. Shellfish spat are attached to at least some of the recesses (7) and the tray (I) is placed in water so that the spat grow into substantially mature shellfish within the recesses (7). The spat each grow generally in the shape of their respective recess (7) so that the mark is created on the shellfish as it grows.
