Sea trout Salmo trutta and salmon smolts S. salar
were supplied by 2 different smolt hatcheries close to
Bergen with no history of disease. The sea trout stock
were from river Sima (Hardangerfjorden), while the
salmon stock were a commercial breed (originally from
2 different rivers on the west coast of Norway). Initial
mean weight and length of trout and salmon were 42 g
and 15 cm, and 48 g and 16 cm, respectively. The fish
were acclimatised for 8 d to particle (20 pm) and UVfiltered
(Katadyn Jl/P, effect: 50 mW cm-2) seawater
(34%0)k, ept at 12.5"C in 0.15 m3 tanks (flow rate = 5 1
min-'; 50 specimens in each tank), and fed commercial
pellets twice a day.