Diseases of fish, crustaceans and molluscs
Like all animals, wild and farmed fish and shellfish experience disease problems. These may be broadly classified into infectious and non-infectious diseases. However, it is not always easy to make a strict division between these as non-infectious causes can stress fish and render them more susceptible to disease agents such as bacteria and viruses.
Fish and shellfish, unlike mammals, are cold-blooded animals and all their physiological processes, including their ability to mount an immune response to pathogens, are greatly influenced by water temperature. Similarly, the pathogens which affect fish are also influenced by water temperatures which means that diseases and diseases outbreaks are often seasonal in their occurrence which varies between diseases, some occurring during the colder winter months, with others predominantly occurring during the warm summer months.
Details of the listed diseases and their current status in Scotland
Disease Management Areas
Disease Management Areas were established in the Final Report of the Joint Government/Industry Working Group on Infectious Salmon Anaemia in January 2000, based on separation distances around active farms, taking into account tidal excursions and other epidemiological risk factors. Farms with overlapping separation distances will usually be within the same disease management area.
Recommendations include that all sites within the same disease management area follow an acceptable stocking strategy (see figure 10.1 in A Code of Practice To Avoid and Minimise the Impact of ISA) such that fallowing within a disease management area is synchronised. Fish farmers are encouraged to look carefully at the areas before stocking sites. Stocking a previously unused site that may bridge disease management areas should be avoided. Fish farmers should consider not re-stocking a site if it would create a "fire break" and split one of the larger disease management areas into two smaller areas.
New sites that would have no effect on exisiting disease management areas or are in disease management areas of their own, pose less of a risk to the spread of disease than those which bridge disease management areas. There is a general presumption against farming at new sites that bridge existing disease management areas.
The Disease Management Area Maps will be updated when a change in site use leads to a significant change in a disease management area, but if you require a map showing the effect of stocking or inactivating a specific site please contact the Duty Inspector at the Fish Health Inspectorate.