MORTALITY SURVEYS AS A TOOL FOR STUDYING MARINE ANEMIA IN SEAPEN-REARED CHINOOK SALMON, ONCORHYNCHUS-TSHAWYTSCHA (WALBAUM)

Because of their rapid autolysis and post mortem contamination, the ex amination of dead seapen salmon has been considered of limited value f or investigating disease in farmed salmon, Marine anaemia is a recentl y described plasmacytoid leukemia of farmed salmon that is diagnosed p rimarily by histological findings, The objectives of this study were t o determine if marine anaemia could be reliably diagnosed in dead fish under commercial conditions and to identify the factors that affect t he quality of data that are derived from mortality surveys, Surface mo ribund fish and dead salmon were recovered from four adjacent pens on 31 farm visits to commercial salmon farms over a 6-month period. Morta lity surveys provided six times as many fish for gross pathological di agnosis and three times as many fish for reliable histological diagnos is of marine anaemia than did surveys of surface moribund salmon, The interval between recovery of dead fish from a pen most strongly influe nced the quality of information derived from the mortality surveys. Mo rtality surveys proved to be more sensitive to finding the disease tha n did surface morbidity surveys. The results demonstrated that mortali ty surveys can provide reliable information, which can generate new in sights not only into the impact and epidemiology of marine anaemia, bu t also for other fatal diseases of seapen salmon.