Shell-disease in the oyster (Ostrea edulis L.), characterized by the occurrence of green rubber-like spots and warts in the shell's interior, next to serious shell malformations and heavy mortality, broke out in the years following 1930 in the Dutch centre of oyster culture, the Oosterschelde. This disease seriously menaced the Dutch oyster culture and threatened it with extinction. Investigations carried through in the field revealed bit by bit the secrets of this once so mysterious disease. A fungus thriving abundantly in old green cockle shells, used in tremendous quantities as cultch in the years 1920-1930 on now abandoned bottoms proved to be the source of infection. The spores of the fungus are distributed by water currents and are able to perforate thin, newly made parts of the oyster's shell. Irritation of the oyster's living tissues ultimately leads to ' irreversible changes, de- formations and death. Uniformities in the spreading of the disease have been traced and could be used to find out how to evade infection, where and when to expect it, and in what intensity. Wholesale cleaning away of old useless shells of Cardium and Crepidula, next to disinfecting young oysters recently attacked, in which a solution of an organic salt of mercury is used, are the methods of control devised by us and adopted by the Dutch oyster farmers. |
