The infectivity by different routes of exposure and shedding rates of <i>Aeromonas salmonicida</i> subsp. <i>salmonicida</i> in Atlantic salmon, <i>Salmo salar</i> L., held in sea water

Abstract

Abstract. The infectivity of the bacterial fish pathogen Aeromonas salmonicida subsp. salmonicida to Atlantic salmon, Salmo salar L., in sea water was investigated and found to be similar to that reported for fresh water. The minimal infective dose in short duration bath exposures (1–3 days) was 10 4 colony‐forming units (cfu) per ml, while prolonged exposure for three weeks, but not for 1 week, produced infection with 10 2 cfu/ml. Intragastric intubation of A. salmonicida established infection with doses of &gt;10 5 cfu. Release of bacteria from dead or morbid infected fish was monitored and found to be in the order of 10 5 –10 8 cfu/fish/h. These results emphasize the importance of removing dead fish from farm sites.