Aquaculture and transport in a changing environment: overlap and links in the spread of alien biota.

Aquaculture has been practiced for some millennia. The speed and access of different transport modes in the spread of cultured species, their pests, parasites, diseases and associates, has changed over this time. There now exists an overlap and interlinking of different transport networks with further routes planned. Coupled with environmental changes and habitat alterations alien biota are presented with further opportunities to become more widely distributed. The certainty of the responsible pathway for the arrival of an alien species is not always easily deduced unless imported directly. A scheme for classifying different levels of certainty is proposed. Aquaculture itself consists of different cultivation intensities ranging from part to all of a species life-history and are classified accordingly in this account. It is inevitable that further species intended for cultivation will be utilized in different world regions and that other biota, some considered to be harmful, will also be transmitted. Nevertheless there are codes of practice such as those used by the IMO and ICES that can reduce some risks.