Oysters are grown in trestles and bags. The trestle is from 20 inches to 26 inches in height is 3 metre long and carries 6 bags. The oyster 'seed' (the baby oysters) used in Ireland is bought in from oyster nurseries in France or the UK. These start off very small going down to just 6 mm in size. The mesh size in the bag varies according to what seed is grown. For example 6mm seed is put into 4mm mesh bags at a ratio of 1000 to 1500 seed per bag. Over a two or three year period these grow to market size, between 60 or 80 to the kilo, by which stage they are in bags of about 120. At 1500 Euros per tonne these are big business.