To examine the influence of the dietary ratio of (n‐3) to (n‐6) polyunsaturated fatty acids (PUFAs) on the immune system of Atlantic salmon, Salmo salar L., two dietary trials were carried out in which parr were maintained on diets containing either fish oil [(n‐3)/(n‐6) PUFA = 5.2] or sunflower oil [(n‐3)/(n‐6) PUFA = 0.3] and assessed for differences in immunological parameters. There were no significant differences in blood cell counts, differential leucocyte counts or haematocrit values between dietary groups, and while no apparent differences were observed in the non‐specific immune parameters measured, there was a significantly higher number of B cells responding to Aeromonas salmonicida, in the kidney and spleen of vaccinated fish maintained on high (n‐3)/(n‐6) PUFAs diets. There was also a significant difference (P≤ 0.01) between the dietary groups in trial 1 and trial 2 when non‐vaccinated fish were challenged with Aeromonas salmonicida and Vibrio anguillarum, respectively, with the (n‐6) group succumbing to the bacterium before the (n‐3) group. The results suggest that Atlantic salmon fed diets with a low ratio of (n‐3)/(n‐6) PUFA may be less resistant to infection than those fed diets containing lipid with a high (n‐3)/(n‐6) PUFA ratio.

No abstract

The localization of a live, and a formalized vaccine preparation of Aeromonas salmonicida within the tissues of rainbow trout, Salmo gairdneri, was followed over a 5 day period. When presented by intraperitoneal injection, both the live bacteria and the vaccine localized in the spleen, liver, kidney and gut. When presented orally, the bacteria and the vaccine were confined almost exclusively to the gut region. Direct immersion resulted in low detectable levels within the tissues, with the spleen and kidney localizing the Aeromonas after its initial attachment to the outer surfaces of the fish.