Genetic considerations in transfers and introductions of scallops

As the potential of scallop aquaculture becomes increasingly realised, transfers (movement within a species' range) and introductions (movement outside a species' range) of scallops are becoming more common. To predict the genetic consequences of transfers, information on genetic differences between source and recipient populations is vital. Morphological, allozyme and DNA based data on genetic differentiation of scallop populations and scallop sub-species are presented and discussed. Other considerations are the numbers of individuals transferred and whether they are wild stock or hatchery product. Loss of genetic diversity is difficult to avoid in hatchery conditions although there are ecological advantages to using disease-free hatchery seed. Mitochondrial DNA data indicating significant genetic consequences of the introduction of Argopecten irradians from the USA to China are discussed and compared with data on Patinopecten yessoensis introduced from Japan to Canada. Potential risks and consequences of hybridisation should be experimentally assessed before introductions of scallops are carried out. Hybridisation is unpredictable and can lead to loss of genetic diversity or breakdown of co-adapted gene complexes. The use of sterile triploid scallops for introductions to avoid hybridisation and reduce ecological impact has merit but reversion to diploidy may occur.