Clinical specimens. Blood specimens were obtained from trout farmed in
northern Italy. Ten rainbow trout (Oncorhynchus mykiss Walbaum) from a pond
with a high level of mortality due to L. garvieae as well as 10 antibiotic-treated
rainbow trout from the same farm but another raceway were sampled randomly.
In addition, 10 rainbow trout from a farm without disease where the fish were
vaccinated against L. garvieae and 10 rainbow trout from a different farm with no
reported disease or mortality but where the disease had occurred a previous year
were also sampled randomly. Half a milliliter of blood was taken from each of the
anesthetized rainbow trout. Heparin at a final concentration of 10 U/ml (Kamada,
Beit Kama, Israel) was added.