Mussels are very common worldwide. Cultured mussels are usually rope grown in Scotland. They take approx 18 months to reach marketable size. The advantage in quality they hold over 'wild' mussels is that because they are not gathered on the seabed they don't have any grit in them. They tend to have cleaner shells and because they are suspended in the water all the time, not inter tidal they can feed constantly and therefore the meat ratio is much higher.
