Piscirickettsia salmonis, a serious bacterial pathogen of farmed marine fish, previously considered culturable only in eukaryotic cell-culture systems, was grown for the first time on agar and broth containing enhanced levels of cysteine, thus greatly increasing the potential for isolation, in vitro culture and study of this organism. Virulence towards Atlantic salmon following passage on agar media was retained in a controlled laboratory trial. Of the studied temperatures, optimal growth on agar was observed at 22 degrees C.

No abstract

In this study, we wanted to evaluate genetic variation in resistance to infectious pancreatic necrosis (IPN) in a breeding population of rainbow trout. Two hundred families were challenged at a commercial test station, using methods that were previously developed for testing resistance to IPN in Atlantic salmon. Thirty-¢ve days after the challenge the accumulated mortality was 26%. The results show that resistance to IPN is moderately heritable in the tested population (h 2 50.30). The genetic correlation between IPN resistance and body weight was found to be low and non-signi¢cant. The signi¢cant additive genetic variation found in IPN resistance after a controlled challenge test gives promise for successful breeding for increased resistance to IPN in rainbow trout.