Analysis of a company's production data to describe the epidemiology and persistence of pancreas disease in Atlantic salmon (Salmo salar L.) farms off Western Scotland

Abstract

Epidemiological studies of pancreas disease (PD) in Scottish farmed Atlantic salmon (Salmo salar L.) were conducted by analysing a marine Atlantic salmon farming company's production data on over 60million fish between 1998 and 2009. Presumptive PD diagnoses were made by farm managers with advice from fish health professionals. Mortality ascribed to PD was negligible before 2003 but rose to a peak in 2006 and 2007, accounting for 94% and 86% of disease losses in 2006 and 2007 respectively, followed by a decline in 2008 and 2009. PD mortalities primarily were reported in larger fish (2–5kg) and accounted for the largest loss in biomass due to any infectious disease including infectious pancreatic necrosis (IPN). The mean monthly numbers of fish lost to PD were higher in July through September. The distribution of mortality between PD infected production cycles was highly skewed with one production cycle accounting for 26% of the total reported mortality. The results showed no evidence that PD in a production cycle was related to a subsequent PD outbreak (with an odds ratio of 0.93 relative to farms that had not experienced PD however this OR has large confidence intervals). The analysis of the industry production data has provided information on the prevalence, intensity and spread of PD in Scotland at a level of detail and, crucially, over a relatively long period that would be impossible to obtain from official statistics on this non-notifiable disease.