Publication Abstract

Aquaculture now supplies nearly half the fish and shellfish that are eaten globally. As with other farmed animals, they are affected by a range of bacterial diseases. These can have severe impacts on both productivity and their welfare. Despite the development in recent years of improved vaccines that effectively control some important diseases, such as furunculosis in Atlantic salmon, antimicrobials are still used to control many conditions. These are typically applied either in feed or direct to the culture water, with varying levels of controls in place to control their useage in different countries worldwide. This use of antimicrobials has very likely driven the development of resistance in the bacteria associated with farmed fish and shellfish. As well as posing a threat to the sustainability of the use of these important chemotherapeutants to treat infected fish, there is also concern that much of this resistance is encoded by so-called 'mobile' genetic elements that transfer the genes from otherwise harmless types of bacteria. Together with the resistance genes, come a whole host of genes of unknown function which may confer an entirely different selectable phenotype. The reservoir of genes which transfer under the selective pressure of antibiotic usage in the aquatic environment is largely unknown. A large body of scientific evidence shows that bacteria harbouring these mobile AMR genes are widely disseminated, and often at high prevalence, in all environments studied to date (e.g. soil, mining waste, livestock production sites, water treatment effluent, marine and freshwater water column and sediment samples). The potential threat that these environmental 'reservoirs' of mobile AMR genes pose to human and animal (including fish) health has not yet been ascertained, but is likely to be considerable. For this presentation we will discuss the extent to which aquaculture practices are affected by, as well as may contribute to, these significant AMR issues.