CATARACTS IN FARMED ATLANTIC SALMON (SALMO-SALAR) IN IRELAND, NORWAY AND SCOTLAND FROM 1995 TO 1997

From 1995 to 1997 cataracts were observed in Atlantic salmon (Salmo sa lar) in Ireland, Norway and Scotland at around the time of smoltificat ion (when freshwater fish become adapted to the hypertonic seawater) i n both fresh- and seawater fish. Over 38,000 fish were screened for th e presence of cataracts. Posterior cortical cataracts were the earlies t and most consistent change, followed by perinuclear, equatorial and anterior cortical cataracts. On histological examination vacuolation o f the lens fibres was consistently present in the posterior cortex. Th e pattern of the outbreak suggested that a nutritional factor was invo iced although the variable incidence and severity of the condition ind icated that a number of modifying factors may have been involved in th e expression of the condition.