219. Mutilations of farmed fish are relatively uncommon. They are limited to a few specialised areas of the industry, where individual fish, or populations of fish, are marked, so that they may be distinguished from one another. Such areas include broodstock production, selective breeding programmes and other areas of research and development such as vaccination or feed trials. Fin clipping, whereby part of one of the fins, usually (in salmonids) the adipose fin, is cut off is sometimes carried out. So is external tagging which involves the attachment of a small plastic tag bearing a unique identifier to the body, the fins or the gill cover. Other methods employed include dyeing of the skin and insertion of micro-tags into insensitive tissue.