Pathogens and parasites generally cause poor welfare in fish. Hence, it is important to manage fish so as
to minimise disease. A key aspect of this is to have
good methods of inspecting fish to recognise those that
are diseased, distressed or dead. As a result of efforts
to reduce or avoid the widespread use of antibiotics in
fish farming, vaccination is used frequently. However,
because of the handling involved and the use of irritant
adjuvants, welfare can be very poor for short periods
because of immediate effects of handling, and poor for
long periods because of increased injury and pathology (Sørum & Damsgaard 2003).