Influence of artificial wound and non-intact mucus layer on mortality of Atlantic salmon (Salmo salarL.) following a bath challenge withVibrio anguillarumandAeromonas salmonicida

Three groups of Atlantic salmon, in two trials, were exposed toVibrio anguillarumorAeromonas salmonicidain a bath challenge. The three groups were: fish with an artificial wound; fish with a non-intact epidermal mucus layer caused by removal of the mucus layer during a swabbing procedure; and a control group with an intact mucus layer. When fish were challenged withV. anguillarum, a non-intact mucus layer caused significant elevated mortalities. Elevated mortalities were also found among the wounded fish, but only significantly in one of the trials. When challenged withA. salmonicidathe wound caused significant elevated mortalities. Elevated mortalities were also found among the fish with a non-intact mucus layer, but only significantly in one of the trials. It is concluded that the mucus layer represents a hindrance withV. anguillarum, whileA. salmonicidaseems to be able to penetrate through it. Removal of the mucus layer on two occasions modifies the new mucus layer which simplifies the entrance ofV. anguillarum. It is suggested that this is a result of a lowered concentration of compounds with anti-vibriotic activity. Wounds appear to be important invasion routes forA. salmonicida.